Distribution Category:Physics -General
(UC - 34)
ANL-83-25
AN--83-25
DES3 014014
ARGONNE NATIONAL LABORATORY9700 South Cass Avenue
Argonne, Illinois 60439
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PHYSICS DIVISION ANNUAL REVIEW
1 APRIL 1982--31 MARCH 1983
Donald S. Gemmell
Division Director
June 1983
1id . . ph
Preceding Annual Reviews
ANL-80 -94ANL-81-79ANL-82-74
1979-19801980-19811981-1982
FOREWORD
The Physics Division Annual Review presents a
broad but necessarily incomplete view of the research
activities within the Division for the year ending in
March 1983.
At the back of this report a complete list of
publications along with the Division roster can be
found.
TABLE OF CONTENTS
NUCLEAR PHYSICS RESEARCH
Introduction 1
1. MEDIUM-ENERGY PHYSICS RESEARCH 3
A. STUDY OF PION REACTION MECHANISMS 5
a. Study of the Pion Absorption Mechanism in 3 He 5through the (Tr+,2p) and (1~, pn) Reactions
b. Study of mow-Energy Pion Absorption in 3He 6
c. Study of Pion Absorption Through the A(Tr,p)X 8Reaction at T, = 500 MeV
d. Survey of Inclusive Pion Scattering Near the A339Resonance
e. Inclusive Pion Charge-Exchange Reactions 11
f. Isospin Dependence of the 18,160(7 , wo) Reactions 13
g. Study of the (Tr,Irp) Reaction and Quasifree 15Scattering in 4 He
h. Measurement Near Threshold of 9Be(3He,IT) to the 15A = 12 Isobaric Triplet by Recoil Detection
i. The A Dependence of the (e,e'p) Reaction in the 16Quasifree Region
B. NUCLEAR STRUCTURE STUDIES 17
a. Inelastic Scattering of Pions by 10B and 1B 17
b. Inelastic Pion Scattering from 14 N 19
c. Excitation of 8-, Particle-Hole States in 54Fe 20
d. Iso alar Quenching in the Excitation of 8 States 22in Cr
e. Excitation of 8 States in 52Cr 22
f. Polarized Proton Scattering from 26Mg 23
V
Transverse Electron Scattering by 2 6Mg
Inelastic Scattering of p + 48Ca at 160 MeV
Study of the 4He(1~, r+) Reaction at Small Angles
Discrete States from Pion Double-Charge-Exchange onHeavy Nuclei
C. TWO-NUCLEON PHYSICS WITH PIONS AND ELECTRONS
a. Energy and Angular Dependence of Tensor Polarizationin Pion-Deuteron Elastic Scattering
b. Tensor Polarization in Electron-Deuteron ElasticScattering
c. Feasibility Study of Electron Scattering Experimentswith a Tensor Polarized Deuterium Target in anElectron Storage Ring
d. Deuteron Tensor Polarimeter Development
e. Photoneutron Physics
D. WEAK
a.
b.
c.
d.
e.
f.
g.
h.
INTERACTIONS
Neutrino Oscillations at LAMPF
Beta Decay of Polarized Nuclei and the DecayAsymmetry of 8Li
A Test of V-A Positron Decay
The Beta Decay Rate of 1 6 N(J - 0', 120 keV); MesonExchange Currents and the Induced PseudoscalarCoupling Constant
0+ + 0- Beta Decay of 1 6 C Ground State
The B anching Ratio to the 160 Ground State forthe 19N Ground State
Neutron Beta Decay
Study of the 1 0 B(2-, 5.11 MeV) and lOB(2+, 5.16 MeV)Levels
vi
g."
h.
is
is
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25
25
27
27
29
29
30
32
33
33
35
35
36
39
39
40
44
45
47
E. PARTICLE SEARCHES
a. A Cryogenic Experiment for the Detection ofFractionally-Charged Particles
b. A Search for Super-Heavy Particles in Cosmic Rays
c. A Search for Axions from Nuclear Decays
F. MEASUREMENT OF THE ELECTRIC DIPOLE MOMENT OF THE NEUTRON
G. GeV ELECTRON MICROTRON
a. Workshop on High-Resolution a'd Large-AcceptanceSpectrometers
b. Microtron Development
II. RESEARCH AT THE TANDEM AND SUPERCONDUCTING LINAC ACCELERATOR
A. HIGH ANGULAR MOMENTUM STATES IN NUCLEI
a. Gamma Spectroscopy at Very High Spin in 147Gd
b. Shape Change in 153Dy
c. Lifetime Measurements in 154Dy
d. Shape Changes at High Spin in 155Er
e. Lif mc 5 easurements of Continuum Statesin ' Er
f.
g.
h.
i.
j.
Measurement of Feeding Times in 152Dy
Yrast Population Patterns in a Wide Range of Nuclei
The (nh11 /2)6 Spectrum in 152Yb
Spectroscopy of 100Cd
Prolate and Oblate Rotational Bands in 186Hg
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49
49
50
51
53
55
58
58
59
61
61
63
64
65
66
67
67
68
69
69
Page
B. FUSION OF HEAVY IONS 73
u. Fusion of 6 4Ni + 112, 11 4 ,116,1 1 8 ,1 2 0 ,12 2 ,1 2 4 Sn 73
b. Fusion of 5 8Ni + 112,1 1 4,116, 1 1 8 ,12 0,12 2 ,12 4 Sn 75
c. Fission of 6 4Ni + 112,114,116,118,120,122,1245n 75
d. Delayed Alpha-Decay of Evaporation Residues Formed 77in Fusion Reactions
e. Atomic Charge States of Evaporation Residues 79
f. Prompt Compound-Nuclear K X-rays in Fusion Reactions 79Induced by a Heavy Projectile
g. Suppression of Neutron Emission in "Cold" Heavy-Ion 80Fusion
C. REACTION MECHANISMS AND DISTRIBUTION OF REACTION 83STRENGTHS
a. Reactions o Resolved States of Nonfusion Channels 83for 160 + 8Ca at Elab = 158.2 MeV
b. Inelastic Scattering tpd Sine-Nucleon Transfer 83Reactions Induced by 0 on Ca at Elab(1 0) =150 MeV
c. Measurement s of Evaporation Residues Produced 86in 160 + 2 Mg at 4 S Elab(160) S 9.5 MeV/A
d. Time-of-Flig~ Measurements of Evaporation Residues 88Produced in Si-Induced Reactions
e. Fusion Cross Section Measurements for 20Ne + 40Ca at 90
Elab(2 0Ne) - 150 and 220 MeV
f. Study of Direct Reactions in the System 37C1 + 20 8Pb 91at Elab = 250 MeV
g. Spectroscopic Studies of 23 4Th with the (180,160) 91Reaction
h. Large Neutro -Transfer Cross Sections Observed 94in SNi and 8Ti Induced reaction on 208Pb
i. Observation of Characteristic Gamma Rays from Quasi- 97Elgtic and Deep-Inelastic Fragments in the 5 8Ni+ Ni Reaction
Page
D. ACCELERATOR MASS SPECTROMETRY 99
a. Measurement of the Half-Life of 4 4 Ti via Accelerator 99Mass Spectrometry
b. Search for Doubly-Charged Negative Ions via 102
Accelerator Mass Spectrometry
c. Accelerator Mass Spectrometry of 4 1 Ca 103
d. Measurement of the Half-Life of 6 0 Fe Using the 107Tandem-Linac System as an Accelerator MassSpectrometer
E. SELECTED NUCLEAR SPECTROSCOPY AT THE TANDEM-LINAC 111
a. Laser Spectroscopy of Radioactive Atoms 111
b. Search for Transient Electric Field Gradient Acting 112on Fast-Moving Ions in Solids
c. The 7 Be(p,Y)8Be Reaction 112
d. Resonances in 7Be(a,Y) and 7Li(a,Y) 114
e. The 7Be Decay Branching Ratio 115
F. EQUIPMENT DEVELOPMENT AT THE TANDEM-LINAC FACILITY 11
a. Ray-Tracing Corrections for the Focal-Plane Counter 117at the Spectrograph
b. Test of the Large Focal-Plane Counter for the Linac 119Magnetic Spectrograph
c. A AE-E Detector for Fusion Measurements 119
d. Modifications to the 65" Scattering Chamber for Long 120Flight-Path Measurements
e. The Y-ray Facility 120
f. Superconducting Solenoid Lens Electron Spectrometer 121
g. General-Purpose Beam Line 122
h. Nuclear Target Making and Development 123
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III. THEORETICAL NUCLEAR PHYSICS 125
A. NUCLEAR FORCES AND SUBNUCLEON DEGREES OF FREEDOM 127
a. Three-Body Forces in Light Nuclei and Nuclear Matter 128
b. Present Status of the Nuclear Saturation Problem 130
c. Studies of Three-Body Forces and Isobar Degrees of 130Freedom in Nuclear Systems
d. Nucleon-Nucleon Potentials with Isobars 134
e. Consistency of Electromagnetic Current Operators and 136Relativistic Wave Functions
f. Relativistic Quantum Mechanics of Particles with 137Direct Interactions
g. Static Bag Source Meson Field Theory 137
h. Monte Carlo Method for Chiral Bag Models 138
B. VARIATIONAL CALCULATIONS OF FINITE MANY-BODY SYSTEMS 139
a. Ground States of Quantal Many-Body Systems 139
b. Monte-Carlo Variational Calculations of 4 He Droplets 140
c. '-shell Hypernuclei and A-nucleon Interactions 142
d. Alpha-Cluster Calculations of Be and Be 143
C. NUCLEAR SHELL THEORY AND NUCLEAR STRUCTURE 145
a. High Spin States in 91 Tc 145
b. The 6~ States in 2 8Si 145
c. Contribution of Giant Dipole State to Coulomb 146Excitation of 6Li and 7 Li
d. The Effect of the A(1236) on the g-facto:- of 147Nucleons
e. Beta Decay of 160(0+) to 16 N(0-) 147
f. Analysis of Inelastic Scattering of Pions 149
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D. INTERMEDIATE ENERGY PHYSICS 151
a. Phenomenological Many-Body Hamiltonian for Pions, 151Nucleons, and A Isobars
b. A Microscopic Study of A-Nucleus Dynamics 152
c. Absorption of Pions by the A = 3 Nuclei 155
d. Electroproduction of A from Light Nuclei 155
e. A Nonstatic DWIA Model for Pion Scattering 157
f. Production of Hypernuclei by Few GeV Electrons 157
g. A Model of Elastic and Inclusive P-Nucleus 159Scattering Above 500 MeV
E. HEAVY-ION INTERACTIONS 161
a. Analysis of 28Si + 28Si Scattering 161
b. Analysis of 1 60 and 180 Scattering from 54Fe 162
c. Extension of the CEOM Calculations 162
F. OTHER THEORETICAL PHYSICS 165
a. Angular Momentum near Solenoids and Monopoles 165
b. Triplet Correlations in Spin-Aligned Deuterium 165
IV. THE SUPERCONDUCTING LINAC 167
A. PROTOTYPE HEAVY-ION SUPERCONDUCTING LINAC 169
B. INVESTIGATIONS OF SUPERCONDUCTING-LINAC TECHNOLOGY 171
1. Superconducting Accelerating Structures 171
a. The ATLAS Resonator 171
b. Resonator Accelerating Field 173
c. Restoration of Performance 173
d. Slow-Tuner Controller 174
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2. Time-of-Flight Technology 174
3. Superconducting Magnets 175
a. Prototype Bending Magnet 175
b. Heavy-Ion Beam Splitting 175
4. Near-Term Plans 176
C. THE ATLAS PROJECT 176
V. ACCELERATOR OPERATIONS 181
A. OPERATION OF THE TANDEM-LINAC ACCELERATOR 183
1. Operation of the Accelerator 183
2. Status of the Superconducting Linac 186
3. Linac Improvements 187
a. Resonators 187
b. Slow-Tuner Pressure Control 187
c. Liquid-Nitrogen Distribution 187
d. Helium Compressor 187
e. Energy-Measurement System 187
4. Upgrading of the Tandem 188
a. Computer Control and Monitoring of the Tandem 188
b. West Injector 188
c. Control of Tandem-Terminal Voltage 188
d. Focusing Lens in Terminal 189
e. Foil Stripping 189
5. Ion-Source Development 189
a. Ion-Source Test Facility 189
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b. Inverted Sputter Source 190
c. West Injector for the Tandem 190
d. The SNICS Source 190
e. Hydrogen Loading 191
6. Near-Term Plans 191
a. Accelerator Operation 191
b. Linac Improvements 191
c. Tandem Improvements 192
d. Ion Sources 192
7. Assistance to Outside Users of the Superconducting 192Linac
a. Experiments Involving Outside Users 194
b. Outside Users and Institutional Affiliations 196
c. Summaries of Major User Programs 197
B. OPERATION OF THE DYNAMITRON FACILITY 203
1. Operational Experience 203
2. University Use of the Dynamitron 205
VI. DATA ACQUISITION AND ANALYSIS SYSTEMS 209
A. On Line 209
B. Off Line 209
C. Future 209
xiii
ATOMIC AND MOLECULAR PHYSICS RESEARCH
Introduction 211
VII. PHOTOIONIZATION-PHOTOELECTRON RESEARCH 213
a. Photoelectron Spectra of the Lanthanide Trihalides 214and their Interpretation
b. Photoelectron Spectra of Metal Oxide Vapors of Group 216III
c. Photoelectron Spectrum of B202 217
d. Photoelectron Spectrum of AiF 217
e. Photoelectron Spectra of BiX3 and BiX 218
f. Photoionization of Atomic Chlorine 218
g. UV-laser Photodissociation of Molecular Ions 220
VIII. HIGH-RESOLUTION LASER-rf SPECTROSCOPY WITH ATOMIC ANDMOLECULAR BEAMS 221
a. Hyperfine Structure of the Excited A 2n State of CaF 221
b. The Hyperfine Structure of Alkaline-Earth Monohalide 223Radicals: New Methods and New Results, 1980-1982
c. New Line Classifications in Ho I Based on High- 223Precision. hfs Measurements of Low Levels
d. Modification of Apparatus for Electric-Dipole Moment 224Measurement through the Stark Effect
IX. BEAM-FOIL RESEARCH AND COLLISION DYNAMICS OF HEAVY IONS 225
a. Lamb Shifts and Fine Structures of n = 2 Helium-like 225Ions
b. Precision Wavelength Measurements in Hlium 227
c. Position-Sensitive Detector for UV Spectroscopy 227
d. High-spin States in Neon 228
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e. Multicharged Tons at the Dynamitron 228
f. Measurement of the Transition Probability of 229Singlet-Triplet Intercombination Lines in Neon
g. Optical Measurements of Molecular-Ion Fragmentation 220
X. INTERACTIONS OF FAST ATOMIC AND MOLECULAR IONS WITH SOLID AND 231GASEOUS TARGETS
a. Contribution of Field-Ionized Rydberg Atoms to 232Convoy Electron Spectra
b. Microwave Field Ionization of Fast Rydberg Atoms 233
c. Coherent Stark States in Foil-Excited Fast Rydberg- 235
Atoms
d. Equilibration Lengths of K-Vacancy Production in 237Solids
e. Analysis of Molecular-Ion Stopping Power 237Measurements
XI. THEORETICAL ATOMIC PHYSICS 239
a. Transitions Between Quartet States of Three-Electron 241Ions
b. Influence of Increasing Nuclear Charge on the 241Rydberg- Spectra of Xe, Cs+ and Ba+
c. Collapse of the 4f Orbital for Xe-like Ions 241
d. Photoionization of the Inner 4d Shells for Xe-Like 242Ions
e. Energy Level Scheme and Transition Probabilities of 242Cl-like Ions
XII. ELECTRON SPECTROSCOPY WITH FAST ATOMIC AND MOLECULAR-ION 243BEAMS
a. Investigation of Rydberg- States Formed in Foil- 243Excited fast Ion Beams
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b. InkLer-Shell Vacancy Fractions in Foil-Excited Ion 245Beams
c. Laser-Stimulated Ar L-Shell Excitation in Slow Ion- 245Atom Collisions
d. Simultaneous Laser- and Ion-Beam Excitation of a Na 248
Vapor Target
e. Further Investigations of the Formation of Rydberg 248States in Fast Ion Beams
f. Study of Li- and He-Autoionization as a Function of 248
Projectile Velocity and Charge State
g-. Auger-Electron Production Following- Ion Collisions 249in Solids
PUBLICATIONS FROM 1 APRIL 1982 TO 31 MARCH 1983 251
STAFF MEMBERS OF THE PHYSICS DIVISION 265
xvi
NUCLEAR PHYSICS RESEARCH
Introduction
The research program in nuclear physics in the Physics Division
spans a broad range of activities and contributes to many of the major
questions in the discipline. Activities may be roughly divided into three
broad categories. Research with the tandem-linac in heavy-ion physics is
doing well, though laboring under severe budgetary constraints, and outside
use of the facility has increased substantially. Progress on the
construction of the full ATLAS facility is coming along expeditiously and
it is expected to be completed on schedule in 1985. In medium-energy
physics, activities are continuing at LAMPF, as well as other accelerators,
though considerable effort was devoted this year to the preparation of a
proposal for a national electron accelerator facility. The medium-energy
experiments are concentrated (a) on understanding pion propagation and
absorption in nuclei, (b) studies of weak interactions and particularly a
neutrino-oscillation experiment at LAMPF, (c) studies of the two-ti..leon
system, and (d) some nuclear-structure experiments. The third major area
of activity is in nuclear theory where the role of sub-nucleonic degrees of
freedom .in.the nucleon-nucleon force and in nuclear matter are explored and
studies of the shell-model theory of nuclear structure are carried out, as
well as work on reaction theory in both the heavy-ion and the intermediate-
energy regime.
Some of the highlights of the past year are in the continued
improved operation of the superconducting linac, where outside user
-arfcipation has almost doubled to near 50% of the research.
The construction of ATLAS is proceeding well and there is every
reason to expect that it will come into operation on schedule.
Evidence has been found from gamma-ray studies for prolate-to-
oblate shapt changes in Dy isotopes.
Studies of fusion cross sections over a range of Ni - Sn isotopes
have revealed a striking- change (~ order of magnitude) over the 20% range
in neutron excess.
2
In medium-energy physics a survey of inclusive charge-exchange
(n no) reactions has been carried out over a variety of targets, showing
great sensitivity to the neutron excess. This complements the study of
inclusive pion inelastic scattering experiments done previously--
experiments which were fully analyzed and published during- the past year.
The importance of pion exchange currents in axial vector beta
decay has been conclusively demonstrated through studies of the 16N_ beta
decay.
A substantial proposal was prepared for a 4-GeV electron
microtron, GEM, which would serve as a major national center for the study
of electromagnetic interactions in nuclear physi s.
The role of the first non-nucleonic degree of freedom, the A, in
the nucleon-nucleon force, in the wave function of the three-nucleon
system, and in nuclear matter has been explored through theoretical
calculations.
A precision measurement was carried out of the branching ratio in
the decay of 7Be which refuted a recent experiment that could have led to
substantive changes in astrophysical calculations and had a direct bearing
on the solar neutrino problem.
3
I. MEDIUM-ENERGY PHYSICS RESEARCH
INTRODUCTION
The medium energy research in the Argonne Physics Division hasmade exciting progress in 1981--1982. Argonne experiments with pion beamsat LAMPF and TRIUMF have elucidated several new features of pion-nucleusinteractions. The dynamics of pion absorption in nuclei were explored intwo-nucleon-coincidence measurements and these experiments have already ledto a more complete understanding of the absorption process. Inclusivemeasurements of pion charge-exchange reactions have provided newinformation on the partition of the reaction strength and the isospin
dependence of the delta-nucleus optical potential. Nuclear structurestudies exploited the unique features of medium energy probes to examinethe response of the nuclear medium to spin-excitations which have a directbearing on the mean pionic field in the nucleus. Polarization measurementsin pion and electron induced reactions on the deuteron revealed substantialproblems in understanding the dynamics in this simplest nucleus. Studies
of the weak interaction have revealed new information on meson-exchangeprocesses and are testing- the fundamental structure of neutrinos in a
search for neutrino oscillations. Also of fundamental importance areexperiments to measure the electric dipole moment of the neutron and to
search for free quark trapping- at cryogenic temperatures.
The interaction of pions with nuclei has proven to be a rich,multifaceted area of study. Argonne measurements have demonstrated that
more than two nucleons erF involved in the pion absorption process and thishas led to the theoretical suggestion that more than one delta is formedwhen a pion is absorbed. A comprehensive series of measurements on He isunderway to examine the elementary absorption process on a T = 1 pair ofnucleons and the dynamics of three-body absorption. This holds importantconsequences for better understanding of pion absorption and of theinelasticities in the NuN phase shift parameters. New data on pon charge-exchange reactions complement previous charged-pion scattering- data anddifferences between the neutral and charged pion spectra are importantevidence for multi-step processes in pion scattering.
High resolution studies of inelastic pion scattering have focusedon spin-flip excitations which are currently the least-understood modes ofthe nuclear response. Measurements indicate that isoscalar and isovectorspin-flip strengths are quenched compared to theoretical expectations.Complementary measurements of proton and electron inelastic scatteringwhich will give a more complete characterization of these modes ofexcitation are in progress.
An understanding of the behavior of the few-nucleon systems isessential in describing the dynamics of complex nuclei. Measurements ofthe deuteron polarization in pion scattering- provide a central test ofmodels of pion absorption. These data also have important consequences inestablishing the existence of di-baryon resonances. Polarizationmeasurements in e-d scattering- have provided the first experimentalseparation of the deuteron charge and quadrople form factors at non-zeromomentum transfer. New measurements at higher energies will help revealthe nature of N-N interactions at short distances, <1 fm. Feasibilitystudies for a new experiment at an electron storage ring are in progress.
4
Weak interaction studies provide a direct look at thesubstructures of nuclei, since the underlying theoretical concepts areexpressed directly in terms of quarks, leptons, and gauge bosons.Fundamental characteristics of the weak interactions are being explored inexperiments studying neutrino oscillations, neutron beta decay, and theelectric dipole moment of the neutron. These experiments necessitate theconstruction of sophisticated detection apparatus. Low-energy weak-interaction studies are providing new information on meson exchangeprocesses and the induced pseudo-scaler coupling strength in nuclei.Despite a compelling theoretical framework, crucial ingredients in modernfield theories have not been observed as free particles. New high-precision searches are being carried out for quarks, magnetic monopoles andaxions.
5
A. STUDY OF PION REACTION MECHANISMS
Major efforts are in progress to characterize the interactions ofpions with nuclei in studies of the dynamics of the pion asorptionmechanism and pion scattering. The (Tr,NN) experiments on He are crucial
for a partial wave decomposition of the absorption process and can providefundamental information on the inelasticities of the nucleon-nucleon p ase-
shift parameters. Further measurements of 3-body absorption modes in He
and He will provide the basic structure to interpret the large number of
nucleons involved in the absorption process on heavier nuclei. Therelationship between inelastic scattering and absorption is probed ininclusive charge-exchange measurements, where experiments have determinedthe dependence of the distribution of reaction strength on the structure ofthe target. The comparison of these charge-exchange reactions withinclusive charged pion scattering data also provides new information onmultistep processes and the isospin dependence of the average isobarpotential.
a. Study of the Pion Absorption MEchanism in 3 He through the(nr,2p) and (Trpn) Reactions ('. Ashery, D. F. Geesaman,R. J. Holt, H. E. Jackson, S. M. Levenson,II J. P. Schiffer, J. R.Specht, E. Ungricht, B. Zeidman, R. C. Minehart,* R. R. Whitney,*G. Das,* R. Madey,t B. D. Anderson,t and J. Watsont)
In a previous study,' it was found that the (l~,pn) reaction
in 3 He and 4 He was suppressed by a factor of '30 compared with the (Tr+,2p)
reaction. This result indicates that pion absorption on a J=O, T=1 pair of
nucleons is strongly suppressed from that on a J=1, T=0 pair. If pion
absorption proceeds dominantly through the A-N orbital angular momentum L
= 0 or 2, then one would expect absorption on the T = 1 nucleon pair to be
strongly suppressed by conservation of spin and parity. However, a
theoretical calculation which includes the expected NA interaction, fails
to explain these data.
A measurement of the angular dependence of the 3 He(i~,pn)
reaction should provide information on the orbital angular momenta involved
in this process. These measurements are expected to begin in 1983 at
*
University oi Virginia, Charlottesville, Virginia.
tKent State University, Kent, Ohio.'Northwestern University, Evanston, Illinois.
1D. Ashery, R. J. Holt, H. E. Jackson, J. P. Schiffer, J. R. Specht, K.
E. Stephenson, R. D. McKeown, J. Ungar, R. E. Segel, and P. Zupranski,
Phys. Rev. Lett. 47, 895 (1982).
6
LAMPF. The proton-proton angular correlations from the 3He(n ,2p)p
reaction will be studied to determine the two-body ("quasideuteron") and
three-body absorption cross sections. For each detection angle of one
proton, the coincident proton will be detected over a large solid angle;
the measurement will be done for 5 detection angles. Proton-neutron
angular correlations from the 3He(n~,pn)n reaction will be studied to
determine two-body absorption in the 1S0 T = 1 proton pair.
The experiment will be performed in the P3 area utilizing the LAS
spectrometer and eight L0" x 10" x 4" plastic scintillators. The
measurements will be performed at 165, 245 and 315 MeV bombarding
energies. Auxiliary measurements of the 3 He(n+, r+p) and 3He(~,rrn)
reactions will be done at one energy and one pion scattering angle in order
to compare the relative momentum of a proton with respect to the p-n pair
and of a neutron with respect to the p-p pair in 3He. This is relevant for
the absorption measurement where the momentum of the absorbing pair with
respect to the third nucleon determines the width of the two-nucleon
angular correlation. The proposal was approved with high priority and will
be scheduled in 1983.
b. Study of Low-Energy Pion Absorption in 3He (A. Altman,*J. Alster,* K. Aniol,t D. Ashery, B. Barnett, t, D. R. Gill,t
W. Gyles,t R. R. Johnson,T S. M. Levenson,l J. Lichtenstadt,*M. A. Moinester,* R. Sobiev, R. Tacik,t and J. Vincent+)
The reactions 3He(n+,pp) and 3He(f~,pn) were studied at a pion
kinetic energy of TT = 65 MeV at TRIUMF. The 3 He nucleus is the simplest
system in which pion absorption on S = 1, T = 0 and S = 0, T = 1 nucleon
pairs can be studied and compared. Previous measurements of pion
absorption on the deuteron provided information only on the S = 1, T = 0
case at low density. The present 3He studies should help better understand
*Tel Aviv University, Israel.
tUniversity of British Columbia, Vancouver, B.C., Canada.
1TRIUMF, Vancouver, B.C. Canada.
University of Toronto, Canada.
Northwestern University, Evanston, Illinois
7
22003He (r+, 2P)
1800
1400-
':1000U)
S600-
V 3He (rK, pn)
b 60-
40
20
0* 40* 80* 120* 160*004op
F:g. I-1. The 3He(iPP) angular distributions are shown in the irNN center
of momentum. The solid lines are Legendre polynomial fits to the data.
8
the nucleon-nucleon interaction, the role of the A in pion absorption, and
the mechanisms of pion absorption in heavier nuclei. This 65-MeV
experiment is one of a series of planned experiments to be carried out at
165 MeV < T, < 300 MeV at LAMPF, using stopped pions and 110-Meg pions at
SIN, and at 25 MeV < TT < 85 MeV at TRIUMF. The ratio R = 3He+pn)(+3g
was found to be (3.4 .4)%. The n-3He+pn angular distribute show
significant asymmetry about 900 in the wNN rest frame as shown in
Fig. I-1. This implies a mixture of odd and even partial waves in the
final state which must be due to some ton-resonant [no A(1232) in the
intermediate state] contribution in the reaction mechanism.
c. Study of Pion Absorption Through the A(r,p)X Reactionat T. = 500 MeV (D. Ashery, R. J. Holt, H. E. Jackson,R. D. McKeown,* J. P. Schiffer, R. E. Segel,t K. E. Stephenson,and and J. R. Specht)
The angular dependence of inclusive proton spectra from (ir,p)
reactions on targets of 3He, 4He, C, Ni and Ta was measured for a pion
kinetic energy of Tn = 500 MeV. The data indicate that 3--5 nucleons
participate in the absorption process, a number similar to that observed in
Exp. 350 at pion energies near resonance.1 This is surprising since it
indicates that the number of nucleons involved in the absorption process is
independent of the 'IN + A coupling strength. In response to the earlier
ANL data, G. Brown et al.2 have recently suggested a novel model in which
absorption proceeds through the formation of two A's rather than one, i.e.
from an SU(4) quark model the n + 2N + AN + 2A process is favored over the
r + 2N + AN + 2N process. Since the two A's are then likely to decay by
involving two more nucleons, this model provides a natural explanation for
the absorption occurring on four nucleons. A manuscript describing the
data is in preparation.
*California Institute of Technology, Pasadena, California.
tNorthwestern University, Evanson, Illinois.
1 R. D. McKeown, S. J. Sanders, J. P.Schiffer, E'. E. Jackson, M. Paul, J.
R. Specht, E. J. Stephenson, R. P. Redwine, and R. E. Segel, Phys. Rev.
Lett. 44, 1033 (1980).
2G. E. Brown, H. Toki, W. Weise, and A. Wirzba, Phys. Lett. 118B, 39
(1982).
9
d. Survey of Inclusive Pion Scattering Near the Aq Resonance(E'. P. Colton, D. F. Geesaman, R. J. Holt, H. E. Jackson,S. M. Levenson,* J. P. Schiffer, J. R. Specht, K. E. Stephenson,B. Zeidman, R. E. Segel,* P. A. M. Gram,t and C. Goulding*)
A comprehensive series of measurements of inclusive pion
scattering from 4Hc, 1 2C, 58Ni and 20 8Pb with the LAS spectrometer have
been completed. Pion energy spectra were measured at 7 angles from 30* to
460 for the solid targets and at 5 angles from 300 to 1460 for the liquid
helium target. Complete data were obtained at n incident energies of 100,
160 and 220 MeV; more limited data were obtained on an H20 target at 100
MeV, on 12C at 300 MeV and on i~ scattering from 12C and 208Pb at 160 MeV.
Each pion energy spectrum i.s dominated by a large peak at an
energy near that corresponding to pions scattering from a free nucleon.
This indicates the importance of the quasifree reaction mechanism even in
the presence of strong pion absorption. Indeed, the spectra look rather
similar for each target and the angular distributions follow the
free n-nucleon angular distribution at back angles. At forward angles
however, the significant yield of low-energy pions cannot arise from the
quasifree mechanism and the yield in the quasifree peak is lower than that
expected from a free-nucleon-like angular distribution. These observations
signal the importance of higher-order processes and Pauli blocking effects
in the reaction mechanism.
The energy dependence of the distribution of reaction strength
for the n+ + 4He reaction is somewhat different from that observed on the
heavier targets as a consequence of the tight binding of the 4He nucleus.
Total inelastic scattering cross sections have been obtained for
each target by integrating the energy and angular distributions. The A
dependence of these cross sections is shown in Fig. [-2. Inelastic
*Northwestern University, Evanston, Illinois
tLos Alamos National Laboratory, Los Alamos, New Mexico.
'Florida A & M University, Tallahassee, Florida.
1D. Ashery, I. Navon, G. Azuelos, H. K. Walter, and F. Schleputz, Phys.
Rev. C 23, 2173 (1981).
10
100
3E
--()
.JW
500
100
500
500
IOO
50H. * PRESENT DATAo ASHERY et al.*0
I I
10A
. I
100
Fig. 1-2. The total inelastic cross sections are shown as a function of A.The solid lines are proportional to A- 4 . The open circles are fromthe results of Ref. 1.
1 1 1
T +=220MeV
&- 160 MeV
1 -
IOOMeV
opop
I I
11
scattering accounts for between 30% to 70% of the total reaction cross
sections for these nuclei.
This work has been completed with the submission of a
comprehensive paper presenting the results.
e. Inclusive Pion Charge-Exchange Reactions (D. Ashery,H. W. Baer,* J. D. Bowman,* M. D. Cooper,* J. Comuzzi,t A. Erel,*D. F. Geesaman, R. Chefetz,t R. J. Holt, H. E. Jackson,M. Leitch,*, R. P. Redwine,t R. E. Segel, J. R. Specht,K. E. Stephenson, D. R. Tieger,|I and P. Zupranski )
An experiment to study inclusive iF0 spectra from pion charge-
exchange reactions with 160-MeV wr was performed using the 'n0 spectrometer
at the LEP channel at LAMPF. This experiment is a continuation of our
studies of inclusive pion charge-exchange reactions which were previously
carried out at lower energies. The 7r0 spectra were measured at 0*, 400,
70*, 1100 and 1500 on targets of 12C, 1 4C, 58Ni, 12 0Sn and 20 8Pb. Analysis
of the measurements is under way. This experiment will establish the A
dependence of the total charge-exchange cross sections. A comparison of
the spectra of this experiment with those previously measured for inclusive
pion inelastic scattering provides an estimate of the importance of
multistep processes. Angular distributions for the energy-integrated cross
sections on 20 8Pb are shown in Fig. 1-3. The neutrL.i excess gives rise to
larger (g+ ,or0) cross sections by increasing the number of nucleons which
can participate in the (r+ ,ir ) reaction while increasing the inelastic
scattering and absorption channels which compete with charge exchange in
the (n~,r0) reaction. Furthermore, the quasifree mechanism is strongly
inhibited at very forward angles due to Pauli blocking.
*Los Alamos National Laboratory, Los Alamos, New Mexico.
tMassachusetts Institute of Technology, Cambridge, Massachusetts.
*Tel Aviv University, Israel.
Northwestern University, Evanston, Illinois.
IlBoston University, Boston, Massachusetts.
I ' I8070
60
50
Pb (7r~,
rT)
I
Pb(7r+,
Jj
I I I I160*
Fig. 1-3. Angular distributions for inclusive (7r+, o) (circles) and (u~,1rO)(triangles) reactions of 160-MeV pions on 2 0 8 Pb.
12
I I' I
rT)
401
30
o20
E
Nb
-v i098765
4F-
I I0*
I I
40 800 1200
8ab
m m N m m or m
I
I I 1 1 1
13
f. Isospin Dependence of the 18, 160(Ir ,rro) Reactions(D. Ashery, H. W. Baer,* J. D. Bowman,* M. D. Cooper,*J. Comuzzi,t A. rzl,t D. F. Geesaman, R. Chefetz,* R. J. Holt,H. E. Jackson, M. Leitch,* R. P. Redwine,t R. E. Segel,J. R. Specht, K. E. Stephenson, D. R. Tieger, IIand P. Zupranski )
The inclusive differential cross sections for (Il ,nw") reactions
on 160 and 180 were measured at 160 MeV with the LAMPF 110 spectrometer.
This experiment was designed to study the isospin dependence of the partial
cross sections for inelastic scattering, charge exchange, and absorption.
Previous measurements of the inelastic scattering and the sum of charge
exchange + absorption show substantial differences in the distribution of
reaction strength on these two targets. By combining these data with
the 12C and 1 4C data described in the previous section, differing effects
of the valence nucleons being in the p shell or the s-d shell can be
identified
The (r+ , ro) cross section was found to be '30% larger on the T =
1 isotope than on the T = 0 isotope of each element while the (n~,n0 ) cross
section was '15% smaller on the T = 1 isotope. The (n+, no) energy spectra
on 160 are compared to (Tr,Tr') spectra in Fig. 1-4. The differences in
these spectra suggest that (r ,wo) reactions couple more weakly to the
absorption channel than do charged-pion inelastic scattering reactions.
*Los Alamos National Laboratory, Los Alamos, New Mexico.
tMassachusetts Institute of Technology, Cambridge, Massachusetts.
*Tel Aviv University, Israel.
Northwestern University, Evanston, Illinois.
Boston University, Boston, Massachusetts.
1D. Ashery et al., Phys. Rev. Lett. 50, 482 (1983).
14
500 - -60 (7r+, M+')-
40 16 0(+,_o) -100
SXI -80300 - 30* '' i. .
(30*) i/, ~60200- $1 .- .*_ 40100 -; - 'X - -20
0 50050* -06 _
200U- (5*) -X 40 k
+ 100 - * -u-"- ..'-S20 k
80* * ~-60 S800200 (80)* t.f.
L 100 - -20
400 -rX 1 I0I0
W300 -A. (1080) 80 g - ' 60 C
-0 2 0 0 -. so- 440 -4 0
10 - -20
0c 0
0 1 I x I
0 50 100 150T.,,.( MeV)
Fig. I-4. Outgoing pion spectra from the l6O (+ ,+') reaction (C. H. Q.Ingram et al. to be published) at 163 MeV and the 160(nr+,Tro) reaction at160 MeV. The ratio of the scales is that of the corresponding pion-nucleon reactions. Angles in parentheses correspond to the (n+,,o)reaction. The lines are theoretical calculations [M. Thies, Nucl. Phys.A382, 434 (1982)] using the A-h model (solid lines) and the closureapproximation (dashed line).
15
g. Study of the (rr,rp) Reaction and Quasifree Scattering in 4 He(D. Ashery, D. F. Geesaman, R. J. Holt, H. E. Jackson, J. P.Schiffer, J. R. Specht, K. E. Stephenson, B. Zeidman, R. E. Segel,*and P. A. M. Gramt)
The measurement of inelastic pion scattering observed in
coicidence with a recoil proton was proposed for a target of 4 He. Angular
distributions will be obtained for n+ energies of 160, 220, and 350 MeV.
Emergent pions will be detected in the LAS spectrometer while an array of
scintillation counters that span a large solid angle will be used to detect
protons.
Data resulting from the coincident observation of pions and
recoil protons should provide a clear indication of the validity of the
impulse approximation in describing the scattering and of the importance of
contributions from higher order processes. The proposal was approved and
is expected to be scheduled in FY 1984.
*Northwestern University, Evanston, Illinois.
tLos Alamos National Laboratory, Los Alamos, New Mexico.
h. Measurement Near Threshold of 9Be(3He,7r) to the A = 12 IsobaricTriplet by Recoil Detection (R. D. Bent,* M. C. Green,* M. Hugi,*J. J. Kehayias,* P. Kienle,t H. J. Scheerer,t W. Schott,t andK. E. Rehm)
Study of composite-projectile pion production to discrete states
in the product nucleus can be extended close to threshold by using the
large solid-angle Indiana University Cyclotron Facility QQSP spectrometer
in conjunction with a heavy-ion focal-plane detector to obtain 4W detection
efficiency. In favorable cases, complete angular distribtions and total
cross sections for n~, r , and n+ production may be obtained simultaneously
with a single angle and magnetic field setting. We studied in a first
experiment the reaction 9 Be( 3 He, n) to the A = 12 isobaric triplet at E =
180 MeV. It was possible to identify 1 2 C and 1 2 B products in the focal
plane detector. The data are presently being analyzed by the Munich group.
*Indiana University Cyclotron Facility, Bloomington, Indiana.
tTechnical University, Munich, W. Germany
16
i. The A Dependence of the (e,e'p) Reaction in the QuasifreeRegion (D. F. Geesaman, W. S. Freeman, R. J. Holt,S. M. Levenson,* X. K. Maruyama,t R. E. Segel,* J. P. Schiffer,E. Ungricht, C. F. Williamson,* and B. Zeidman)
A proposal to study the A dependence of the (e,e'p) reaction at
q = 540 MeV/c at the Bates electron accelerator has been submitted. From
the A dependence of the ratio of (e,e'p) coincidence to (e,e') singles
events the mean free path of 140 f 20 MeV nucleons in nuclei will be
deduced. This information on the proton mean free path is essential for
the analysis of pion absorption phenomena and inclusive proton-induced
reactions. At the present time, proton elastic scattering data support a
long mean free path (--6 fm) while the inclusive proton data seem to require
a smaller value. The electron knockout reactions appear to be the cleanest
technique to provide macroscopic and microscopic measures of this
fundamental nuclear parameter.
*Northwestern University, Evanston, Illinois
tNational Bureau of Standards, Washington, D.C.
*Massachusetts Institute of Technology, Cambridge, Massachusetts.
17
B. NUCLEAR STRUCTURE STUDIES
Medium-energy probes can examine many new features of nuclearstructure due to the unique and differing selectivities of the Tr-nucleus,e-nucleus, and p-nucleus reactions. Measurements of pion inelasticscattering utilizing the EPICS system have established a quantitativeunderstanding of the pion-nucleus reaction mechanism. The isospinstructure of the pion-nuclear interaction can be used to separate neutronand proton transition amplitudes and makes pion scattering the ideal toolto study isoscalar and isovector spin-flip modes in nuclei. Theseexperiments have identified a systematic quenching of the isoscalar andisovector spin-flip strength to high-spin particle-hole states.Complementary data from proton and electron scattering reactions areimportant in establishing the underlying quenching mechanism. Otherexp iments have studied the momentum dependence of magnetic form factorsin Ca and searched for resonant structure in the four-neutron system.
a. Inelastic Scattering of Pions by 10B and 1 B (B. Zeidman,D. F. Geesaman, C. Olmer,* G. C. Morrison,t G. R. Burleson,*J. S. Greene,* C. L. Morris, R. L. Boudrie,R E. Segel, IL. W. Swenson, G. S. Blanpied,** B. R. Ritchie,** C. Harvey,ttand P. Zupranskill)
Elastic and inelastic scattering of n+ and ~ by targets of 10B
and "1B was studied at T, = 162 MeV. Angular distributions between 200 and
90* were measured in 50 steps for n+ and 7~. In addition, spectra were
obtained at 3 angles each at T, = 130 and 250 MeV, namely angles
corresponding to momentum transfers where the differential cross sections
for 2 = 2, 3, and 4 are maximized. For nuclei with T # 0 the isospin, the
energy dependence, and the angular distributions of the cross sections
allow multipole decompositions of mixed electric and magnetic transitions -
separately for neutrons and protons. Among the results are evidence, shown
in Fig. 1-5, for a rotational band built upon (lp 2 ,1d5 /2)4- neutron
particle-hole configurations. The transition to the 11/2+ state at 14.04
MeV excitation is found to be severely quenched. Preliminary results were
presented in a paper at the international conference in Amsterdam, 1982.
*Indiana University, Bloomington, Indiana.
tUniversity of Birmingham, Birmingham, England.
*New Mexico State University, Las Cruces, New Mexico.
Los Alamos National Laboratory, Los Alamos, New Mexico.
IlNorthwestern University, Evanston, Illinois.
Oregon State University, Corvallis, Oregon.
**University of South Carolina, Columbia, South Carolina.
ttUniversity of Texas, Austin, Texas.
18
7r100 4e . 2C
50 - 7.29MeV- I
20 ,
10 -
5-
2-
I-100- ,,9.19MeV
50 -/ . 9.27MeV -C
20 -/10 ,5:
50 4 1.29MeV
20-
10- -
5-
2-
I 14.,04 MeV20 -1/2)_
15- 1/
I0-8-6-
4-
0 40 800 1200
c.m.
5
0086
4030
00
5
080
60
40
0080
60
40
36
- -
. 4 .
.4 .
-
-il''
++ +++--
20a
15
1086
100
50
20
10
5
2
lo00-
50
20
10~
5
2
-a A --j4
7r +511111III
(5/2+)4
- 4 , e -
- -,
200150
1008060
4C30
10080
60
4030
'.,.(5/2+) 20-
0 (9/2+)-20
15 --00- -0-
8-
56
2 4
0* 400 800 120 120 2406c~m. INCIDENT PION
ENERGY (MeV)
7 +
- m -
-4
4-
3-
120 240INCIDENT PIONENERGY (MeV)
Fig. 1-5. Angular distributions and excitation functions at fixedmomentum transfer for inelastic pion scattering by 11B. The curves areDWIA calculations for T, = 162 MeV; the solid curves are based upon thenuclear structure calculations while the dashed curves include theadditional 4~ contributions to the cross sections that are deduced fromthe vi excitation functions.
(7/2f) -
/
/ +
-I ,
-
-o
b10
19
b. Inelastic Pion Scattering from 14N (D. F. Geesaman, C. Olmer,*B. Zeidman, G. C. Morrison,t G. S. Blanpied,* G. R. Burleson,*R. L. Boudrie, R. E. Segel, HR. E. Anderson,and L. W. SwensonI)
Elastic and inelastic scattering of 163-MeV pions from 14N was
studied with the EPICS spectrometer at LAMPF. CH2 N2 and CH2 targets were
employed at each angle, and the nitrogen spectra were constructed by
subtraction. Many 1 4N levels between 3 and 24 MeV were observed, but only
an upper limit could be set on the cross section for the 0+ T = 1 state at
2.31 MeV excitation. Angular distributions were obtained for 18 states.
The majority of the states are excited by L = 3 transitions. A state at
14.7 MeV appears to be a 5 state which is predicted by shell-model
calculations to be strongly excited in pion-inelastic scattering. Two
additional states, at 16.9- and 17.5-MeV excitation, may also be 5 states
and show some evidence of isospin mixing. Microscopic DWIA calculations
have, some success in describing the states observed. The project was
completed with the submission of a paper.
*Indiana University, Bloomington, IndLana.
tUniversity of Birmingham, Birmingham, England.
*New Mexico State University, Las Cruces, New Mexico.
Los Alamos National Laboratory, Los Alamos, New Mexico.
IlNorthwestern University, Evanston, Illinois.
Oregon State University, Corvallis, Oregon.
20
c. Excitation of 8 Particle-Hole States in 54Fe (B. Zeidman,D. F. Geesaman, R. D. Lawson, C. Olmer,* A. D. Bacher,*R. L. Boudrie,t C. L. Morris,t R. A. Lindgren,* G. R. Burleson,S. J. Greene, W. B. Cottingame, R. E. Segel, II L. W. Swenson,rand W. H. Kelly**)
The scattering of n+ and n~ by 54Fe was studied at T = 162 MeV
utilizing the EPICS system at LAMPF.' Particular interest was placed upon
the excitation of 8 states that result from particle-hole configurations
of the form (1f 7/2-1 ,1g 9 /2)8-. Since 54Fe has a neutron excess, both
isoscalar and isovector interactions contribute to excitation of T = 1
states while only the isovector interaction leads to T = 2 states. As a
result, different spectra are obtained from n+ and ir scattering. The data
are compared to theoretical nuclear structure predictions in Fig. 1-6.
Reasonable agreement can be obtained between the experimental results and
theoretical calculations if the isoscalar contributions are quenched by a
factor of ~2 relative to isovector contributions. The basis for this
quenching is under investigation.
*Indiana University, Bloomington, Indiana.
tLos Alamos National Laboratory, Los Alamos, New Mexico.
*University of Massachusetts, Amherst, Massachusetts.
New Mexico State University, Las Cruces, New Mexico.
IINorthwestern University, Evanston, Illinois.
Oregon State University, Corvallis, Oregon.
**Montana State University, Bozeman, Montana.
1 R. A. Lindgren et al., Phys. Rev. Lett. 42, 1524 (1979).
21
8-STATES IN 54Fe
-- THEORY
-----t EXPT.
(e ,el)
T T1TI II I
7r
IIT
11 - I ' ?i fI I
10
T1 II
8 10EXCITATION
T
I
_aaI s I '
12ENERGY
Fig. 1-6. Comparison of (e,c') M8 transition strengths and (ir,ir') peakcross sections (dashed lines) with theoretical calculations (thin lines).The calculations have been normalized to the yield for the 13.26-MeV T-2state. The heavy solid lines show the results of the calculations whenthe isoscalar transition strength is reduced by a factor of two. Thisreduction is required to obtain agreement with the pion inelasticscattering data.
0
0
C'
88
50
40
30
20 11IC
CU)
13
b-V
8
40-
30-
20-
10-
iiI
14
1
14(MeV)
01
IH-
50 -
40-
I
I
I
I
I
I
I
30-
201
io
I.i
f
10 12 14
I I
12
22
d. Isoscalar Quenching in the Excitation of 8 States in 52Cr(D. F. Geesaman, R. V. F. Janssens, B. Zeidman, G. C. Morrison,*R. L. Boudrie,t C. L. Morris,t G. R. Burleson,* S. J. Greene,*and L. W. Swenson )
A proposal has been submitted to LAMPF to use the EPICS system in
an investigation of the properties of 8~ states in 52Cr excited by the
scattering of 162-MeV rr+ and n~. Previous results for pion scattering
by 54Fe show that stretched transitions to 8 states with configurations
(f7% 2 g91 2)8- are observable with reasonable cross sections. The
experiment is directed toward answering a fundamental question concerning
"quenching" in inelastic scattering. The present experiment, in
conjunction with experiments utilizing other probes, should indicate
whether or not quenching of isoscalar transitions relative to isovector
transitions is merely an artifact of inadequate structure calculations or
requires a new quenching mechanism. In addition, information regarding the
absolute magnitude of the quenching should be obtained. This experiment
has been approved and is scheduled to run in 1983.
*University of Birmingham, Birmingham, England.
tLos Alamos National Laboratory, Los Alamos, New Mexico.
*New Mexico State University, Las Cruces, New Mexico.
Oregon State University, Corvallis, Oregon.
e. Excitation of 8 States in 52Cr (B. Zeidman, D. F. Geesaman,G. C. Morrison,* L. W. Fagg,t D. I. Sober,t X. K. Maruyama,*and R. A. Lindgren $
A proposal has been approved at NIKHEF-K, Amsterdam, for the
study of the inelastic scattering of electrons by 52Cr at 0lab - 1540 for
incident electron energies ranging from Ee = 140 MeV to Ee = 260 MeV, i.e.
q a 1.4 to 2.6 fm-1. Of particular interest are the 8~ states formed by
particle-hole excitations involving (1g9/2, 1f7/2 1)8- configurations. The
*University of Birmingham, Birmingham, England.
tCatholic University, Washington, D.C.
*National Bureau of Standards, Gaithersburg, Maryland.
University of Massachusetts, Amherst, Massachusetts.
23
identification of the 8 states, their locations and the transition
strengths will be compared to theoretical predictions and also utilized in
a study intended to ascertain the origins of quenching in both isovector
and isoscalar transitions. The experiment is scheduled to run in June
1983.
f. Polarized Proton Scattering from 26Mg (D. F. Geesaman,B. Zeidman, C. Olmer,* A. D. Bacher,* G. T. Emery,*C. W. Glover,* H. Nann, W P. Jones,* S. Y. van der Werf,tR. E. Segel,* and R. A. Lindgren )
We have measured the angular distributions and analyzing powers
for polarized proton scattering from 26Mg at 135-MeV incident energy at the
Indiana University Cyclotron Facility. A typical spectrum at 350
laboratory angle is shown in Fig. 1-7. Angular distributions were measured
in 50 steps from a laboratory angle of 100 to 600 for states in the
excitation energy range from 0 to 20 MeV. Five 6 states have been
identified based on the characteristic angular distributions of the cross
sections and analyzing powers.
This experiment is a continuation of our efforts to understand
the quenching of spin-flip strength in high-spin particle-hole states. The
phenomena are now well established throughout the periodic table for AT = 1
transitions, and are also observed for AT = 0 transitions in pion and
proton scattering. By studying the inelastic strength as a function of
deformation in the s-d shell, and as a function of angular momentum
transfer, we hope to distinguish between several proposed explanations for
the quenching mechanism, including the possiblity of isobar-hole admixtures
in the nuclear wave functions.
*Indiana University, Bloomington, Indiana.
tK.V.I., Groningen, The Netherlands.
*Northwestern University, Evanston, Illinois.
University of Massachusetts, Amherst, Massachusetts.
24
.....................................,........ ~ 111 UUUI1 11111 wIDE,~vm
10 15EXCITATION ENERGY (MeV)
Fig. 1-7. A proton spectrum at 350 resulting from the scattering of
135-MeV spin-up protons by 26Mg. This spectrum is a composite of the
data obtained with three field settings of the QDDM spectrometer.
10000
8000-
6000F--JW
I- I ITIT
2 6 mg (''p')
SPIN UPo =350
pII
40001
2000H-
Cl5 20
III-" lilall AIIII IIAll IIIII
TTT1ITrvv vm
TT -IfI
! 1 _ l = i r1 1 f S a m s1 l 1 1 1 1 1 1 l 1 l l 1 1 1 1 1 1II.mblail_ rr Pik i i l 11 11
. i 1I " rvIIIIIIIIIIII191111111 .. r
i
25
g. Transverse Electron Scattering by 26Mg (A. D. Bacher,*D. F. Geesaman, R. S. Hicks,t R. L. Huffman,t R. A. Lindgren,tX. K. Maruyama,* C. Olmer,* M. A. Plum,t and B. H. Wildenthal )
The inelastic scattering of electrons by 2 6Mg was studied using
the 1800 inelastic electron scattering facility at the Bates Linear
Accelerator Laboratory. Initial' preliminary measurements were made at
incident energies of 140 and 192 MeV where the momentum transfer
corresponds to the peak of the transverse form factors for E4 and M6
multipolarities, respectively. Five 6 states were tentatively identified
including the 6~, T = 2 state at 18-MeV excitation. These data along with
that of the previous (p,p') measurement will permit the determination of
the isoscalar and isovector spin-flip strengths for each 6 state. Final
data for this experiment are expected to be taken in early FY 1983.
*Indiana University, Bloomington, Indiana.
tUniversity of Massachusetts, Amherst, Massachusetts.
*National Bureau of Standards, Washington, D.C.
Michigan State University, East Lansing, Michigan.
h. Inelastic Scattering of p + 4 8Ca at 160 MeV (K. E. Rehm,R. E. Segel,* P. Kienle,t D. W. Miller,* and J. R. Comfort )
The investigation of possible mesonic effects on inelastic proton
scattering to the 10.24-MeV 1+ state in 48Ca was completed and the results
have been published.' Cross sections and analyzing powers for low lying
states up to Ex = 9.4 MeV have been extracted. Angular distributions and
analyzing powers for some of the states are shown in Fig. 1-8. Of
particular interest are unnatural parity states (4-) between 5--7 MeV and
some high spin states around Ex = 9 MeV. DWIA calculations for these
states are presently being performed.
*Northwestern University, Evanston, Illinois.
tTechnical University, Munich, W. Germany.
*Indiana University Cyclotron Facility, Bloomington, Indiana.
University of Arizona, Tucson, Arizona.
1K. E. Rehm et al., Phys. Lett. 114B, 15 (1982).
26
I I I I
48Ca (p, p )C48Ca
EIb=I59.8MeV _
I
104
13I0
2102
I00
,*6.342MeV
0e0 (4+)0.00%.
0000
1I
- .. .0 -
0 0 :
5.729MeV -(5~)I-
I __I I I I
500
1.0
C
0.51-
o
a 0.5
0
0.5
o
-0.5
I.'U I
-0.5
-1.010 200 30 40
c.m.
48 -6.(Ca ,1489
C(p, p) CElab=159.8 MeV
00" 0
- "* . ELASTIC* ." -
. *0 .
4* 3.832MeV
+ (2+)
0.,Do
40
1 00
4.507 MeV(3-)
*. ! 0
. SO* 0
6.342 MeV -4 + (4+)
t * * 9.9
"5,
"t01
t *-S*. 5.729 MeV*. (5-)
__I I I 1 I I 1
100 200 30' 4Q0 50 600 70
c.m.
Fig. 1-8. Angular distributions and analyzing powers for low-lying states
in 4 8Ca populated by inelastic n-scattering at ELab = 160 MeV.
000.
.
0e
"1
"
-0
-0
0
0
. ELAST I C
" 0
* * "*.3.832MeV
S . 0 (2 )
* 0
0 0
.0 " "*.... (3)-
U)
E
b
00
10
1O
I0
-
.
""0
w
I
i
-
:-
V
r
I
27/a
i. Study of the 4He(Tr~, n+) Reaction at Small Angles(D. F. Geesaman, S. J. Greene,* R. J. Holt, R. D. McKeown,tC. L. Morris,* J. R. Specht, K. E. Stephenson, J. Ungar,tand B. Zeidman)
A search for structure in the 4n system via the 4He(rr~,Tr+)4n
reaction in the energy range 130--200 MeV was undertaken. The Argonne
Large Acceptance Spectrometer (LAS) was used to detect T+ emerging from a
liquid helium target located slightly upstream of the usual LAS target
position. A 12" diameter circular dipole centered over the pivot deflected
positive pions at 00 toward LAS while deflecting the negative pions from
the P3 beam away from the spectrometer. The efficiency and resolution of
the system were determined by measurements of 12C( ~,T+) double-charge
exchange. Analysis of the data does not reveal any statistically
significant structure in the spectra. An upper limit for the 00 cross
section for the formation of the tetra-neutron is 7 15 nb/sr which is
approximately 2 orders of magnitude lower than previous results.
*New Mexico State University, Las Cruces, New Mexico.
tCalifornia Institute of Technology, Pasadena, California.
*Los Alamos National Laboratory, Los Alamos, New Mexico.
j. Discrete States from Pion Double-Charge-Exchange onHeavy Nuclei (D. F. Geesaman, R. J. Holt, J. R. Specht,
and B. Zeidman)
Eikonal model predictions for analog-state transitions in pion
double-charge-exchange (r+ ,r~) suggest that 00 cross sections for heavy
nuclei should be large and comparable to those for very light nuclei. Near
resonance, cross sections for nonanalog transitions are expected to be
roughly equal to those of analog transitions. The LAS spectrometer,
together with a circular sweeping magnet, will be used to test these
conjectures. A P3 channel failure forced postponement of this experiment
which, because of its relatively short duration, will be rescheduled in
conjunction with another DCE experiment that utilizes LAS.
29
C. TWO-NUCLEON PHYSICS WITH PIONS AND ELECTRONS
After years of effort, an understanding of the N-N interactionremains a central concern for nuclear physics. Measurements ofpolarization observables in pion and electron reactions on the deuteronprovide information on the pion absorption mechanism and on isoscalarexchange currents. The data on the angular distribution of the tensorpolarization in Tr-d scattering cannot be explained by any current theory.During 1982 the tensor polarization t20 in e-d elastic scattering wasmeasured foj the first time. Since the momentum transfer range(1.7--2 fm ) of this measurement is comparable with that of the tensorpolarization measurements in n-d scattering and since good agreement wasfound between the results and calculations which employ reasonable deuteronwave functions, this confirms the suspicion that the discrepancies betweenthe experiment and calculations in n-d scattering arise from an incompleteknowledge of the inelastic channel (nd + NN) rather than of the deuteronwave function.
Studies to continue these measurements at higher momentumtransfer using an electron storage ring are underway. In otherexperiments, low-energy photodisintegration measurements revealed problemswith the conventional nucleon-meson descriptions of the deuteron in
predicting the neutron polarization in the d(y,n) reaction.
a. Energy and Angular Dependence of Tensor Polarizationin Pion-Deuteron Elastic Scattering (R. J. Holt, W. S. Freeman,D. F. Geesaman, J. R. Specht, E. Ungricht, B. Zeidman,E. J. Stephenson,* J. D. Moses,t M. Farkhondeh,* S. Gilad,and R. P. Redwine )
Recent theoretical calculations have shown that the tensor
polarization t2 0 in n-d elastic scattering is sensitive to true pion
absorption and the possible existence of dibaryon resonances. Our previous
measurements of the angular dependence of t20 at T. = 142 MeV do not agree
with the results of present three-body calculations. This indicates that
pion absorption on two bodies is more complicated than previously believed
or there is an effect from dibaryon resonances.
Since a possible resonance effect was suspected, it was decided
to determine both the energy and angular dependence of t2 0 . An experiment
*Indiana University, Bloomington, Indiana.
tLos Alamos National Laboratory, Los Alamos, New Mexico.
*Graduate Student, Massachusetts Institute of Technology,
Cambridge, Massachusetts.
Massachusetts Institute of Technology, Cambridge, Massachusetts.
30
is presently in progress which should provide measurements of the angular
distribution of t20 at 180 and 256 MeV. (In fact, the measurement at 180
MeV is now complete and the data analysis is in progress.) This work
should be completed in 1983.
In response to some recent results from a SIN group, we have
checked the energy dependence between T, = 134 and 151. MeV of t 2 0 at 6d =
18.00. We observed no remarkable energy dependence over this small energy
range. The results of a preliminary analysis agree with our previous
measurement at 142 MeV and we conclude that the SIN data are probably
erroneous.
b. Tensor Polarization in Electron-Deuteron Elastic Scattering(R. J. Holt, J. R. Specht, K. E. Stephenson, B. Zeidman,E. J. Stephenson,* J. D. Moses,t D. Beck,M. Farkhondeh, S. Gilad,* S. Kowalski,* R. P. Redwine,*M. Schulze, W. Turchinetz,* M. Leitch, and R. Goloskie**)
During 1982 the tensor polarization t2 0 in e-d elastic scattering
was measured for the first time. The tensor polarization is dominated by
the charge and quadrupole form factors of the deuteron, and consequently,
it is sensitive to the tensor part of the deuteron wave function and at
high momentum transfer the short-range part of the wave function. The
deuteron tensor polarimeter that was developed in order to measure t2 0 in
n-d scattering was employed at Bates in order to measure the
polarization. The results indicate that the data are in good agreement
with theoretical calculations that use reasonable deuteron wave
functions. In Fig. 1-9, the present work is compared with predictions) of
t20 of the Paris model, both with and without meson exchange current
*Indiana University, Bloomington, Indiana.
tLos Alamos National Laboratory, Los Alamos, New Mexico.
*Massachusetts Institute of Technology, Cambridge, Massachusetts.
TRIUMF, Vancouver, British Columbia, Canada.
Graduate Student, Massachusetts Institute of Technology, Cambridge,
Massachusetts.
**Worcester Polytechnical Institute, Worcester, Massachusetts.
1M. I. Haftel et al., Phys. Rev. C 22, 1285 (1980).
31
0
2 2H(e,e) H
-0.5
t2t20 PA RIS
-I.0-PRESENTWORK
PARIS (MEC)---
-1.50 5 10 15
2 -2q(fm )
Fig. I-9. Comparison of present measurements of t2 0 in e-d elasticscattering with the predictions of the Paris potential with andwithout meson exchange current corrections.
32
corrections, for the deuteron. The agreement with these models is
remarkably good. Cleary, in order to study the meson exchange current
effect one would need either higher accuracy at the low momentum transfer
or push the measurements of t20 to higher momentum transfer. The tensor
polarization was measured for two values of momentum transfer: q = 1.75 and
2.0 fm~l. Since this momentum transfer range is comparable with that of
the tensor polarization measurements in Tr-d scattering, then this indicates
that the discrepancies between the experiment and the calculations in Tr-d
scattering arise from an incomplete knowledge of the inelastic channel (ird
+ NN) rather than that of the deuteron wave function. The results indicate
that it will be somewhat difficult to extend the measurements to higher
momentum transfer even after the energy doubler at Bates becomes
operational. Thus, we are investigating alternative options, such as the
use of a tensor polarized target in an electron storage ring.
c. Feasibility Study of Electron Scattering Experiments with aTensor Polarized Deuterium Target in an Electron Storage Ring(R. J. Holt, L. S. Goodman, J. R. Specht, E. Ungricht,B. Zeidman, J. D. Moses*)
This study is centered around the Aladdin storage ring at
Wisconsin. This ring is expected to be operational in 1983 and is expected
to produce a 1-GeV electron beam with a circulating current of J00mA. In
an experiment of this type baffles will be necessary to localize the target
and to provide differential vacuum pumping. A movable baffle has been
designed and constructed for the ring. This baffle will be employed in
order to study the radiation background, transverse "tails" associated with
the beam and the interaction of the beam in the presence of a baffle. If
this part of the experiment proves feasible, then construction of a tensor
polarized atomic deuterium target would begin in 1983 or 1984.
*Los Alamos National Laboratory, Los Alamos, New Mexico.
33
d. Deuteron Tensor Polarimeter Development (R. J. Holt,E. J. Stephenson,* M. Farkhondeh,t and M. Schulzet)
In order to simplify the high-q measurement of t2 0 in e-d
scattering at Bates, a deuteron tensor polarimeter which has a higher
operating energy and figure-of-merit than those of the existing polarimeter
would be necessary. A search for a suitable reaction was carried out with
the 80-MeV, tensor-polarized deuteron beam available at the Indiana
University Cyclotron Facility. Deuteron elastic scattering and reactions
were studied for 3,4He, 6,7Li, 9Be and 12C. Thus far, no reaction was
found which would lead to an improvement over the existing polarimeter. At
present, the only reaction which offers any hope of improvement is d-p
elastic scattering. It is expected that the cross section and analyzing
power of this reaction will be measured during 1983.
*Indiana University, Bloomington, Indiana.
tGraduate students, Massachusetts Institute of Technology, Cambridge,
Massachusetts.
e. Photoneutron Physics (R. E. Holland, R. J. Holt, H. E. Jackson,R. D. McKeown,.J. R. Specht, and K. E. Stephenson)
The end of 1982 marked the completion of a long series of
photoneutron studies at Argonne. The photoneutron facility has been placed
in a standby mode. During the past year, the photoneutron program centered
around photodisintegration studies of the deuteron. High accuracy
photoneutron polarization and relative angular distribution measurements
were performed in the photon energy range of 5--19 MeV. The angular
distribution for the D(Y,n) reaction is sensitive to E1-E2 amplitudes,
while that for the photoneutron polarization is sensitive to El-M1
interference. It was found that the angular distributions are in
disagreement with the theoretical calculations by 5--15%. This indicates
that the multipole composition of even the simplest photodisintegration
process is not completely understood.
The measurements of photoneutron polarization at a reaction angle
of 90* formally depend on El-M1 and E1-E2 interference terms. However, all
calculations show essentially no dependence on the El-E2 amplitudes. Thus,
34
one would expect the polarization to be sensitive through the M1 amplitude
to meson exchange currents in the deuteron. The trend of the data indicate
possible agreement with the calculation at low energy EY 7.0 MeV, but
clear disagreement at higher energy, ~12.0 ftV. The effect of including
meson exchange currents1 in the theory is to produce an even greater
disagreement between the present results and the calculations.
Although the theories also originally failed to explain the
photodisintegration cross section at 00, an earlier discrepancy, that
disagreement occurred at much higher energies and is now believed to be
explained by relativistic effects. The present work is more surprising
since many effects such as relativity, nucleon form factors, details of the
deuteron wave function and uncertainties in the final-state interactions
are not important at such low energies.
Measurements of the photoneutron polarization at 1350 were also
performed and analysis of the data is in progress.
1E. Hadjimichael, Phys. Lett. 46B, 147 (1973).
35
D. WEAK INTERACTIONS
The goals of the weak-interaction program are to attempt todetermine the structure of weak currents, and to use weak interactions as aprobe of hadronic currents. A search for neutrino oscillations at LAMPFaddresses two central issues in gauge theories of weak interactions, themass and the flavor purity of neutrinos. Argonne has assumed a majorresponsibility in the construction of a large and sophisticated neutrinodetector for this experiment. Low-energy source and accelerator-basedexperiments provide tests of right-handed currents, the conserved vectorcurrent hypothesis and the existence of second-class currents. Theimportance of pion exchange currents in pseu g-scalar bqa deays has beenconclusively demonstrated in studies of the N, 0 to 0, 0 betadecay. This provides a measure of the induced pseudo-scalar coupling-constant for A = 16 of gp = 11 2, close to the free nucleon value of7.0 + 1.5.
a. Neutrino Oscillations at LAMPF (J. Donohue,* S. J. Freedman,C. A. Gagliardi,t G. T. Garvey, L. Hyman,* R. Imlay,M. Kroupa,NU T. Y. Ling, R. D. McKeown,** W. Metcalf,B. Musgrave,* J. Napolitano, T. Romanowski, F and M. Timko )
The possibility and consequences of V oscillations have recently
received much attention because of developments in the extension of gauge
theories to include strong and electroweak interactions. These new Grand
Unified Theories (GUTS) rather naturally produce massive V's and flavor
mixing in the lepton sector among- other striking- predictions. We are part
of a collaboration which has an approved experiment (E645) at Los Alamos
Meson Physics Facility to search for V oscillations. The neutrino source
is to be the LAMPF beam dump which yields Ve, vu and vu neutrinos from
stopped pion and muon decays.
The energies of the V's produced are such that only Ve or ve can
be detected via charge-changing interactions. Two kinds of oscillation
experiments are to be performed. In one the disappearance of electron
*Los Alamos National Laboratory, Los Alamos, New Mexico.
tTexas A & M University, College Station, Texas.
*High Energy Physics Division, ANL.
Louisiana State University, Baton Rouge, Louisiana.
1Thesis Student, University of Chicago, Chicago, Illinois.
Ohio State University, Columbus, Ohio.
**California Institute of Technology, Pasadena, California.
36
neutrinos will be measured by observing the spatial dependence of the
neutrino flux with the reaction (Ve + d) + (e + 2p). The other phase of
this experiment involves the appearance of Ve neutrinos via v + e; the
Ve being detected via ( , + p) + (e+ + n). The latter experiment is the
one being pursued first.
A crucial aspect of this experiment is that it must be able to
reject backgrounds with an efficiency greater than 1-10~7. Argonne has
accepted the responsibility of prototyping, designing, and implementing a
shield to reject backgrounds due to either charged or neutral cosmic
rays. The Physics Division has designed and tested a prototype active
shield for charged cosmic rays. This prototype is a tank of liquid
scintillator with an active volume of 1.5 m x 1.5 m x 15 cm viewed by four
five-inch diameter hemispherical photomultiplier tubes. (See Fig. I-10 for
sc'iematics). Tests of this detector have shown it to be excellently suited
for the task. A typical pulse-height spectrum is shown in Fig. I-ll.We
have drafted a paper on these tests and will submit it to Nuclear
Instruments and Methods.
We are now studying backgrounds due to the neutral component of
cosmic rays. At present, these tests consist of measurements of the energy
deposited in a 10" dia x 10" long NaI(TZ) crystal which do not deposit
significant energy in a plastic scintillator anticoincidence shield
surrounding the crystal. Preliminary results seem to be consistent with
cosmic-ray neutrons, and with bremsstrahlung from the electrons resulting
from muon decays. This effort is continuing.
b. Beta Decay of Polarized Nuclei and the Decay Asymmetry of 8Li(R. Bigelow,* S. J. Freedman, G. Masson,* J. Napolitano,and P. Quin*)
Using the FN Tandem facility at the University of Wisconsin-
Madison and the accompanying polarized ion source, we have begun a program
of studying the weak interaction via the beta decay of polarized nuclei.
Such a study yields information on the validity of CVC, the existence of
second-class currents, and the magnitude of certain nuclear matrix
elements.
*University of Wisconsin, Madison, Wisconsin.
PLAN
A)
FILL PORT
D
0LED
EB')
RUBBER PAD
RETAINING HAMMAMATSURING R1391
FLANGE
VITON 0-RING
CPTUCL NGLUCITE WINDOWCOUPLINGGREASE
ELEVATIONS
I.5m
Fig. I-10. Schematic of the liquid-scintillator-active-shield prototype and hemispherical phototubemounting arrangement. There are four such phototube assemblies on the prototype at locations markedA, B, C, and D. The prototype was studied in a self-triggered mode and with a cosmic-ray telescopeover regions 1, 2 and 3.
E
38
- I ' ' ' ' I ' ' ' - j ' ' ' ' i' ' ' ' -
1000
Cl)
zW 10 0
U--
0
w 10m
z
0 200 400 600 800 1000
PULSE HEIGHT (channels)
Fig. I-11. A pulse-height spectrum from one of the phototubes triggeredon the cosmic-ray telescope. Loose cuts have been made on the telescopedata to eliminate non-single-particle triggers. Tests with the LEDshow that this spectrum corresponds to approximately 1000 photoelectronsemitted on average from the photo cathode.
39
We are presently studying the beta decay of polarized 8Li,
produced with a polarized deuteron beam on a cold target of 7Li metal kept
in a magnetic holding field. The asymmetry between up and down
polarization states is detected by two electron-detection telescopes.
Total electron energy is measured in large plastic scintillators. This
investigation will therefore yield the energy dependence of the decay
asymmetry. Data from our first run are being evaluated and the detector is
being refined.
c. A Test of V-A Positron Decay (S. J. Freedman, G. T. Garvey,J. Napolitano and A. Rich*)
We are considering a possible experiment to measure the helicity
of positrons from nuclear positron decays as a sensitive test for the
presence of V + A currents. The experiment would utilize a novel and very
sensitive polarimeter for positron helicities developed by A. Rich and co-
workers at Michigan. The method utilizes the spin dependence of
positronium annihilation in a magnetic field as a measure of the positron
spin. A possible experiment would require intense sources of 2 6Alm and 30P
that could be produced either at the Dynamitron or the Argonne Cyclotron.
A feasibility study is currently underway.
*University of Michigan, Ann Arbor, Michigan.
d. The Beta Decay Rate of 1 6 N(J1T = 0-, 120 keV); Meson ExchangeCurrents and the Induced Pseudoscalar Coupling Constant(C. A. Gagliardi, G. T. Garvey, S. J. Freedman, and J. R. Wrobel)
We have improved (by a factor 2) our previous measurement of this
important decay. The bulk of the error in the 0~ beta decay rate now rests
with the uncertainty in the decay rate of the Jn = 2 16N ground state
which is under investigation. Apart from this error, currently at 11%, we
have reduced all other sources of error in this decay branch to 4%. The
improvements in the measurement over our earlier result involve higher
statistics and more uniform targets.
40
The 0 + 0+ decay rate is important for quantifying the role of
pions in the nuclear medium. A pseudoscalar transition such as this one is
believed to be effected strongly by the presence of pions in nuclei. Their
strong effect on this transition is just a consequence of the time-like
component of the axial vector current. Sizable meson exchange effects have
long been predicted and detailed calculations have recently been carried
out for the 16N 0 + 0+ case. Thus this particular measurement is
significant as it represents a case where the nuclear structure is both
simple and calculable and the N capture rate between the 160 ground state
and the 16N,JE - 0 120-keV level is well known (Au = 1560 94 sec-).
This ratio of the V capture rate to the beta decay rate is very sensitive
to the pion currents and insensitive to the details of nuclear structure.
Figure 1-12 shows the comparison of theory to the measured decay
probability (Au) along with our measured value of the beta decay
probability (As).
The difficulty in measuring the beta decay rate arises from the
fact that it is a weak decay of an excited state with an electromagnetic
decay rate of AY = 1.32 0.02 x 105 sec-1 . Thus the beta decay branch is
the order of 10-6 of the total decay probability for this level. Using
techniques described in last year's submission we have measured A8 = 0.45 t
0.05 sec-1 . Figure 1-13 shows the beta rate measured as function of time
with respect to a peak burst over an 18-hour run. As stated in the opening
paragraph of this section the bulk of the error lies in the 16N ground
state to 160 ground state decay branch which is used to calibrate the
efficiency of our beta detector system. This work has led to two invited
talks and a Physical Review Letter. A more detailed Physical Review
article is nearing completion.
e. 0+ + 0~ Beta Decay of 1 6 C Ground State (C. A. Gagliardi,G. T. Garvey, N. Jarmie,* and R. G. H. Robertson*)
As part of the effort to establish the role of virtual pions in
nuclei we have measured the beta decay of the 1 6 C ground state to the 0~,
120-keV level of 16N. These pseudoscalar matrix elements are known to be
*Los Alamos National Laboratory, Los Alamos, New Mexico.
41
9P/9A
2
)13
CO
'0
0o 0.2 0.4
A (secs)
Fig. 1-12. Calculation of Towner and Khanna, Nucl. Phys. A372, 331 (1982)compared to experimental value for A and As. The open points are theresult of impulse approximation calculations while the closed pointsinclude meson-exchange currents. Curves are shown for 3 values of
gp/g A"
42
200
160
-
1201
401
OL0
' I
I I I II I
10 20I I I I I I
30 40TIME (psec)
50
Fig. 1-13. The rate as function of time observed in the beta telescope.
The smooth curve is a fit to an exponential (T = 7.8 0.7 ps) plus
a constant background.
(!1F-z
0
60
-4
2 1
I I
I I ' I
I -- TT
J
4 i,141 11 lill. 4i I v TITTiTliT l7fij
801
i
43
' I
-Ssii.".s.
0
S00
0
(a)
"".0
000
00
0 000
12-
.e' 09 g~*"0
I I
250 270I I
-u I I I
I (b)
- " , -
3
4mo *" af * 0
H4
*00
1 l I290 590CHANNEL NUMBER
610 630
Fig. 1-14. The gamma-ray pulse-height spectrum in the region of the120-keV line for 3 different time intervals. The top spectrum isfrom the first time bin. The middle spectrum is taken 0.88 sec. laterand the bottom spectrum is taken 1.94 sec. later. Note 160 has a0.75-sec. half life.
15x103
12
9
12
xl03
C,)F-zD0
61
-13
'2
- -I JI I I T -T -
I I i I II I
44
greatly affected by pion exchange currents and further the transition
matrix elements are very similar to those required to produce AT = 1 parity
mixing in hadronic systems. This experiment represents the first time that
the 0~ branch has been observed in the decay of 16C. The measurement was
carried out at the LANL Tandem Van de Graaff, where 16C was produced via
the 14C(t,p)16C reaction at Et = 6.0 MeV. The use of both a radioactive
beam and target allowed the preparation of a much cleaner and stronger 16C
source than had heretofore been possible. The prominent decay modes of
the 16C ground state are to JTF = 1+ neutron unstable states in 1 6 N. We
detected the neutrons with a stilbene crystal, the betas in a thin (0.8 mm)
plastic scintillator and photons in a 12.5 cm3 Ge(Li) detector. The
absolute efficiency of the Ge(Li) was fixed with calibrated sources while
the beta counter efficiency was determined at ANL using - Y coincidences
in the 20F + 20Ne decay. Our results for the 16C decays are a branching
ratio of 6.8+0' x 10-3 for the decay to the 0 state and a limit of <10-3
for the branch to the 1 state. Figure 1-14 shows the Y-ray energy
spectrum as a function of time in which the branch to the 0~, 120-keV line
is clear.
As this 0+ + 0~ decay depends principally on 21/2 + 1P1/2
transitions the rate depends on the amount of the (2S /2) component in
the 16C ground state. Using an estimate of this component by D. Kurath and
our earlier value for the 16N(0~) + 160 ground-state decay rate, we predict
a value of the 0+ + 0- branch that is 2.5 times what we observed. A proper
calculation of the nuclear structure must be done to determine if we have
achieved a quantitative characterization of these pseudoscalar transitions.
f. The Branching Ratio to the 160 Ground State for the 16N Ground State(A. Heath and G. T. Garvey)
The branching ratio for 16N ground-state decay to the 160 ground
state and 6.13-MeV level are 26 2% and 68 2%, respectively.
Unfortunately, the errors in these determinations are highly correlated so
that the ratio of these branches is 26 2/68+2 = .385 * .040. This
uncertainty is responsible for the bulk of the 11.5% error in our recent
measurement of the beta decay rate of the 1 6 N J= - 0~, 120-keV level as it
entered into the calibration of the beta detector efficiency. Reducing the
45
error in the above ratio to 5% would reduce the error in the 0~ branch to
6.9%.
The measurement of the 1 6N ground-state decay is being carried
out at the Dynamitron using the 15N(d,p)16N reaction at Ed = 1.7 MeV. The
beta rays are being measured in our flat-field beta spectrometer. The
absolute acceptance of the spectrometer is being measured employing --Ycoincidences in the decay of 20F made via 1 9 F(d,p) 2 0 F. We expect to be
able to calibrate the absolute efficiency of this spectrometer to 3--4%
thereby being able to measure the 16N branching ratio to an acceptable
level. This device will also be employed to measure the beta spectra
associated with the fission of 2 55Cf, an experiment which bears on the
questions of Y spectra associated with heavy fissioning nuclei (U2 35).
g. Neutron Beta Decay (S. J. Freedman, D. Dubbers,* Y. Last,*P. Bopp,* H. Schatze,* and 0. Schrpft)
Neutron beta decay represents a unique opportunity to study the
semileptonic weak interaction in a tractable hadronic system. The first
run of a new-generation neutron beta decay experiment was conducted in 1982
at the Institut Laue-Langevin reactor by a collaboration consisting of
scientists from Argonne, Heidelberg, and the ILL. The experimental goals
are to provide a new high-precision value for the average reaction
asymmetry parameter A, a test of the conserved vector current hypothesis
through a measurement of the energy dependence of A, and a value for the
neutron lifetime (at the 1% level) by a new experimental method.
The experimental instrument consists of a ̂ 2m long
superconducting solenoidal spectrometer equipped with two scintillation
detectors. A novel geometry allows us to observe polarized neutron decay
over a large region and thus along with the high flux polarized beam at the
ILL, the resulting count rates are more than two orders of magnitude higher
than previous experiments. The first run of the experiment was completely
successful. Data obtained during the run should provide a value of A with
*Physikalisches Institut, Heidelberg, Germany.
tlnstitut Laue-Langevin, Grenoble, France.
46
1MVT r-T rr rI1V7 r- 1yTIII
- l~)
0000
00
to
0
Cl)
E
0U-
0
W
-o
5 10 15 20 25ELECTRON ENERGY (Channels)
--- III II III I -- --
5 10 15 20 25ELECTRON ENERGY (Channels)
Fig. 1-15. Preliminary results on the S-decay asymmetry of the neutron.The upper figure shows a typical background-subtracted electron energyspectrum. Some unsubtracted background remains at this time at lowenergies. The lower spectrum shows, as a function of electron energy,the asymmetry from polarized neutron S-decay.
2.0
O O-
0 t i i iI i i i O t m h m
1.5
1.0
0.5
0.00
0.075
0.050
0.025
0.000(/1
-0.025
-0.0500
I l l l 1 1 -#+ l 1 11 1 1 1 1 1 1 1 1 1 1 1 ll l 1 1
47
an error five times smaller than the best present values. The v/c
dependence of the asymmetry was observed for the first time and the data
are sufficient for providing a preliminary result for the energy dependence
of A. (See Fig. 1-15.) The ILL management has allocated three running
periods for this experiment during the last half of 1983. The data from
the first run are being analyzed at Heidelberg and Argonne and the
experiment is being refined and improved for the next run. Application of
the present detector to the measurement of other correlation coefficients
is under study.
h. Study of the 1 0 B(2~, 5.11 MeV) and 1 0B(2+, 5.16 MeV) Levels(S. J. Freedman and J. Napolitano)
To better evaluate the feasibility of a new effort to study
nuclear parity mixing due to the weak neutral current in 10B, we have begun
a study of the 2~-2+ doublet in 1 0 B. The resonance width of the 2 level
has been measured with the 6Li(a,y)1 0 B reaction. (See Fig. 1-16.) Values
for the total gamma decay width and the gamma decay branching ratios of
these levels were also obtained. Future experiments will be performed to
measure the a partial-wave decomposition in the 6Li(a,y)10B reaction as
well as the branching ratios for particle and gamma decays from the 2+-2-
doublet. These results will help implement a reevaluation of the current
theoretical expectation for parity mixing in 1 0 B. Possible new experiments
to measure parity mixing in 10 B are being explored.
48
>6000a)
4000
2000
1.155
500
400
300
200
100
0
L16 1.165 1.17 1.175 1.18E~ (DYNAMITRON VOLTAGE IN MV)
Fa(2)LB= (1.63 0.11) KeV
(B)
171 1 1 11 1 111III 1A~
1.065 1.07 1.075I'lILy
1.08 1.085 1.09
Ea (DYNAMITRON VOLTAGE IN MV)Fig. 1-16. (A) Thick-target resonance yield from a-capture on 6Li to the
5.16-MeV 2+, T=1 state in 10 B. The width of this state is 'i 1 eV and canbe neglected with respect to beam spread and Doppler broadening.(B) Thick-target yield from the 5.ll-MeV, 2~, T=0 state in 10B.Integrating the curve in (A) with a Lorentzian of width Fa( 2-)iAB yieldsa good fit to this data (with a total of four free parameters). Theresult Ta(2 -)LAB = 1.63 0.11 keV is consistent with an oldermeasurement reported in the literature.
(A)
1. 11 l i i II11111l
II
0
I I I I I I I I IIII
I L-Lt 1 1 1 1
1 I I 1 1 1
I I I 1 0 1I-A A a a I .
49
E. PARTICLE SEARCHES
Modern field theories are formulated in terms of particles whichhave not been experimentally observed. The experimental identificaton ofone of these particles would provide convincing evidence for the validityof the theoretical approaches. A reported observation of fractionally-charged objects in superconducting niobium led to an accelerator-basedsearch for fractionally-charged objects trapped in cryogenic materials.Grand unified field theories suggest that heavy magnetic monopoles exist.A search for slow-moving- magnetic monopoles is currently underway.
a. A Cryogenic Experiment for the Detection of Fractionally-ChargedParticles (D. Frekers, W. Henning, W. Kutschera, J. P. Schiffer,K. W. Shepard, C. Curtis* and Ch. Schmidt*)
The low-temperature physics group at Stanford has persistently
reportedly the observation of fractional charges on superconducting- Nb
balls. In these experiments a Nb ball of about 100-pg-mass is levitated in
a static magnetic field and the charge is determined from the response of
the ball to an alternating- electric field. Numerous searches in other
laboratories using-a variety of different (room-temperature) techniques
have all yielded negative or inconclusive results. We have therefore
performed an experiment with conditions similar to those of the Stanford
experiment (superconducting- Nb), however using a quite different detection
technique.
One of the intriguing features of the Stanford experiment is the
observation of frequent changes of the fractional charges when a Nb ball
touched a solid surface between successive measurements. This suggests
that the fractionally-charged particles present at liquid helium
temperature are loosely trapped in the superconducting Nb. These particles
should readily be released when the temperature is raised and collection
and acceleration in an electrostatic field should be possible. We have
therefore built a Nb-filament source which could be cooled down to 4.2*K
and rapidly heated up to several hundred *K. This source was installed on
one of the Fermilab 700-kV Cockroft-Walton injectors and energy spectra of
positively-charged particles extracted from the Nb filament were
*Fermi National Accelerator Laboratory, Batavia, Illinois.
1 G. S. LaRue, J. D. Phillips, and W. M. Fairbank, Phys. Rev. Lett. 46,
967 (1981).
50
measured. Careful scans in the interesting energy regions of 1/3 and 2/3
full energy were performed covering a mass range of about 10 MeV/c 2 to
100 GeV/c2 . No significant events were observed for a variety of different
operating conditions. In particular, no increase in counting rate was
observed when the Nb filament was heated from liquid helium to room
temperature.
The mass of the Nb filament in the present experiment was about
1000 times the mass of a Stanford Nb ball. If the fractional charges
observed at Stanford are due to particles trapped in the ball, we should
have seen 100-1000 events in the first few seconds after the heating.
Since we observed no signals above the background of 10-2 per second we
conclude that the fractional charges observed at Stanford are either
carried by particles outside the mass range of our experiment or another
hitherto unknown mechanism is responsible for their appearance.
b. A Search for Super-Heavy Particles in Cosmic Rays(S. J. Freedman, B. Gobbi,* M. Kroupa,t and J. Napolitano)
Grand unified, field theories suggest that there might exist
magnetic monopoles with masses on the order of 101 6 GeV/c2.
Astrophysicists have estimated the production of such objects in the early
universe and some such estimates predict a presently detectable
abundance. Searches for such objects have proceeded primarily along two
fronts. One makes use of flux quantization in superconductors to detect a
moving magnetic pole. The other attempts to identify particles moving with
extremely low velocities (~10~4 c) via ionization energy loss. A good
candidate for a magnetic monopole has been reported by Cabrera at Stanford
using the former technique. The difficulty with the latter technique is
that the level of ionization energy loss (with accompanied emission of
light) is uncertain.
We have undertaken a search for slow-moving particles with finite
energy loss. Using large-area plastic scintillators from a previous
*Northwestern University, Evanston, Illinois.
tThesis Student, University of Chicago, Chicago, Illinois.
515
experiment (designed to search for the low ionization of fractionally
charged particles), we will be sensitive to particles with velocities
between 10-5 c and 10-3 c and which produce light to any appreciable
extent in plastic scintillators. The detectors we are using have been
shown to be sensitive to single photons. Therefore, we will be able to
detect monopoles (or any other slowly moving- particle) if any light is
emitted while traversing plastic scintillator.
Present efforts consist of constructing the superstructure which
holds the scintillator and approximately 1 ton of lead shielding needed to
reduce radioactive background. Data-acquisition electronics have been
designed and are being- constructed by the High Energy Physics Division.
Data-taking should be underway by winter of 1983.
c. A Search for Axions from Nuclear Decays (S. J. Freedmanand K. T. Knopfle*)
Computer studies of the sensitivity of the Max Planck Institute
(Heidelberg) crystal ball detector for observing axion decay have
continued. An attempt to obtain a 5 1 Cr source of ^5 kcuries produced for
calibration of the Homestake Solar Neutrino detector from Oak Ridge was
unsuccessful. Negotiations continue in an effort to find a suitable source
for the experiment in 1983. The experiment will search for axions decaying
into two photons after emission from nuclear decay.
*Max Planck Institute, Heidelberg, Germany.
53
F. MEASUREMENT OF THE ELECTRIC DIPOLE MOMENT OF THE NEUTRON(V. E. Krohn, G. R. Ringo, T. W. Dombeck,* M. S. Freedman,J. M. Carpenter,t and J. W. Lynn*)
The purpose of this project is to measure the electric dipole
moment (EDM) of the neutron. Such a measurement would probably constitute
the most sensitive test of time-reversal symmetry now available. The
present situation is that with about a factor of 10 improvement in
sensitivity, a whole class of gauge theories--those which explain CP
failure by introducing a new scalar field [e.g., S. Weinberg, Phys. Rev.
Lett. 37, 657 (1976)]--can be given a definitive test.
Since the measurement of the neutron EDM is fundamentally a
frequency measurement, its statistical uncertainty is inversely
proportional to the duration of the measurement. It is therefore natural
to try the measurement on ultracold neutrons (UCN). These neutrons with v
< 7 m/s can be kept in a bottle for hundreds of seconds. We propose to do
this using two unique features. First, we propose to use a pulsed neutron
source and keep the inlet to the bottle open only when the pulsed source is
on, thus allowing a buildup to an asymptotic density determined by the peak
flux of the source instead of the average. This has the advantage that
pulsed sources have peak fluxes that are much higher than the average
fluxes of steady state sources of the same average power. Second, we
propose to produce the UCN by Bragg reflection of considerably faster (400
m/s vs 7 m/s) neutrons from a moving mica crystal designed so that the
reflected neutrons are almost stationary in the laboratory system. The
advantage of this is that it avoids the problems of extracting the very
delicate UCN from the hard-to-control environment in a high flux source.
The present state of the project is that both of these ideas have
been tested and shown to be practical as have several other ideas for
enhancing the production of UCN, such as the use of reflectors around the
moving crystal and funnels to concentrate the UCN in real space at the
expense of their concentration in velocity space. The experiment has been
*Los Alamos National Laboratory, Los Alamos, New Mexico.
tlntense Pulsed Neutron Source, ANL.
*University of Maryland, College Park, Maryland.
54
seriously handicapped by the abandonment of the liquid hydrogen moderators
at IPNS and the delay in achieving 100*K moderation.
A very encouraging development however has been the news that the
macropulses of LAMPF at Los Alamos can be used on a spallation neutron
source and that they will be available at one or more places there. This
would represent a gain of a factor of at least 100 over IPNS in the
critical variable of the experiment--density of neutrons in the measurement
bottle. It should lead to a measurement of an accuracy of a few times
10-26 cm x e for the neutron EDM--approximately 10 times better than the
present limit.
55
G. GeV ELECTRON MICROTRON
There is a clearly articulated national need for a high intensityhigh-duty factor GeV electron accelerator, and the stated intention of DOE
is to consider proposals for facility construction to begin in 1985. TheGeV electron microtron (GEM) project at ANL has been engaged in an
intensive effort to develop the technology for such an initiative. GEMscientists have developed a new advanced design for an electron acceleratorwhich meets all the stated design objectives at low capital and operating
cost.1 The new accelerator, called a hexatron because of its six-sided
geometry, will furnish high-qualit" continuous beams in the energy range of800 million electron volts to 4 billion electron volts. A plan view of the
microtron laboratory is shown in Fig. 1-17. The accelerator, a variant ofthe microtron family, is compatible with an existing facility at Argonnewhich is currently unoccupied and available. The replacement cost of thatcomplex, formerly occupied by the Zero Gradient Synchrotron accelerator,would be greater than $50 million. Its use would result in major savingsin capital cost for the new national facility, a key element in the
national plan for nuclear physics. The cutaway view in Fig. 1-18 shows theaccelerator and experimental areas in the existing buildings. GEM would bethe first major high-energy electron accelerator capable of simultaneouslyserving more than one experimental area. The availability of threeindependent electron beams with variable energies in the GeV range, 100%duty factor, and currents of 100 pamps, would open a new and exciting rangeof electron nuclear research which would address many of the mostinteresting questions at the frontiers of nuclear physics. The Argonneeffort has concentrated on an engineering and design study of the sectormagnets which generate the guide fields in the multi-sided configurationswhich would be employed for GeV accelerators. A detailed conceptual designhas been completed for the sector magnets in the hexatron system. Currentefforts are focused on 3-dimensional computational simulations of the fieldprofiles, as a proof of principle demonstration of the design. Todemonstrate scientific feasibility it is necessary to determine the centraland fringe field profiles accurately and include their features in thedevelopment of a system of optical elements giving orbit containment andhigh transmission. Construction of a magnet prototype is planned. Itsdesign will closely approximate that to be used in the working hexatron,but its primary purpose is to serve as a benchmark for 3-D fieldcalculations using newly developed computational techniques. When thereliability of these calculations has been established, they will be usedto optimize the sector magnet design for the best transmitted beam qualityand minimum capital cost.
1H. E. Jackson et al., A National CW GeV Electron Microtron Laboratory,Argonne Report ANL-82-83, December 1982.
BLDG
369
.EIMRS
L T O
MEDIUM
RESOLUTIONAREA
BLDG. 370
/1/,II
BLDG. 368
DATA ROOMS
0 10 20 30 METER
0 50 100 FEE T
~I
HIGH RESOLUTION
.... 4AREA
.ti-,BLDG.
365"
H EX AT RON
MONOCHROMATIC BLDG. 371PHOTON AREA
Fig. I-17. Plan view of the ANL 4-GeV microtron facility showing three experimental areas and
associated beam transport.
U-,0N
57
J .
Fig. I-18. Pictorial view of the ZGS area. The proposed hexatron and
experimental areas are indicated in a conceptual manner. The cut-away
view of the ZGS ring building indicates the proposed location of the
hexatron. The GEM experimental areas and spectrometers are shown as
being housed in the ZGS experimental area buildings.
58
a. Workshop on High-Resolution and Large-Acceptance Spectrometers(B. Zeidman, Editor)
A workshop concerning the present status and future technological
developments for high-resolution and large-acceptance spectrometers was
held at ANL on September 8-11, 1981. The proceedings of this workshop are
available as an informal report, ANL/PHY-81-2.
b. Microtron Development
Assembly and testing of a prototype sector magnet has been
scheduled for completion in 1983. Field measurements made with a precision
of 0.1% and a spatial resolution of 0.5 mm will be completed during this
period. Subsequent calculations using 3-D magnet programs such as TOSCA
will be used to optimize the design. The results will be incorporated into
a model of beam dynamics in the hexatron for establishing accelerator
performance and the electron current threshold for beam breakup. The data
will furnish the base for evaluating alternative designs for a multi-sided
microtron. At this time a decision will be made on a final magnet
configuration which will be incorporated into a design including cost and
time schedules. A construction proposal for a multi-GeV CW electron
accelerator research facility including experimental areas has been
submitted to DOE early in 1983.
59
II. RESEARCH AT THE TANDEM AND SUPERCONDUCTING LINAC ACCELERATOR
Introduction
The completion of the superconducting linac booster has made itpossible to perform experiments on a more-or-less regular basis, withoccasional accelerator shutdown to allow for maintenance and ATLAS building-construction. The development of an improved ion source has made feasibleexperiments with "difficult" beams such as Ca and Ti. The experimentalfacilities are also nearly complete. All these factors have benefitted andstrengthened the heavy-ion research program. The overall, thrust of thisprogram continues to be the systematic study of nuclear structure at high
spin, high excitation energy, and nuclei far from stability; and thedistribution of reaction strengths with increasing- beam energy and theinfluence of nuclear structure on the reaction mechanism. Several newdirections have been developed including investigations of the relaxationprocess following fusion, momentum transfer of evaporation residues, fusionforming very heavy compound systems and shape changes in heavy transitionalnuclei.
Significant information and understanding- of shape transitions innuclei have been obtained from experiments on soft transi Sn n uclei.Striking prolate-to-oblate changes have been observed in Dy, whiledecoupled i1 3/ 1 8geutron bands with both prolate and oblate shapes have beenidentified in Hg. These studies have led to a good description of thenuclear shape as a function of spin and neutron number and to a better
appreciation of the shape-driving force provided by decoupled high-jquasiparticles. Measurements of lifetimes of continuum states and feedingtimes of high-spin yrast states indicate the coexistence of both collectiveand single-particle structures above the yrast line in transitionalnuclei. In the program on proton (h 1/2)n valence structures outside a N =82, Z = 64 core, a long-lived (40- us) isomer was discovered in $Yb82,extending the body of data which is very well predicted by shell-modelcalculations.
Cross-section measurem gts of eporation residues formed inbombardment of Sn isotopes with Ni and Ni have revealed interestingcross-section differences as a function of the neutron number of thecompound nucleus. Experiments are underway to determine whether thisneutron-number dependence is due to differences in compound nucleusformation or differences in fission competition. Residues with lowproduction cross section have been detected through delayed a activity. Theaim of these programs is to elucidate the influence of shell structure infusion, the dynamics of the fusion process, and the survival probability ofheavy residues--of relevance for the production of superheavy nuclei. Theearliest stages following fusion have been probed by measurements ofneutron spectra and neutron multiplicity distributions. Suppression ofneutron emission is observed and may be related to trapping- in asuperdeformed potential well as the initially highly deformed staterelaxes.
While it is well known that the evaporation residue cross section
ceases to increase beyond a certain center-of-mass energy, the exact causefor this phenomenon has not been unambiguously identified. The onset and
60
growth of incomplete fusion, quasifission, deep-inelastic scattering andfragmentation are responsible, but the distribution of reaction strengthwith beam energy has yet to be definitively ascertained. To determine thisdistribution systematic studies will be necessary. The experiments atArgonne focus on measurements of discrete tates2 of the velocities ofevaporation residues. In a study of the Cl + Pb reaction, which is ofthe first type, it has been observed that neutron and proton pick-upchannels dominate the transfer and deep-inelastic reactions,respectively. A broad set of singles and coincidence experiments is basedon measurements of residue velocities, which allow a decomposition of thecross sections associated with full and partial momentum transfer.Interesting- differences in the cross section for complete momentum transferhave been observed in producing the same compound nucleus with differententrance channels.
The accelerator mass spectrometry (AMS) program continues both atthe tandem and at the linac. AMS has been demonstrated to be an extreme}effective tool for measuring very low-level concentrations (10-10 to 10 )of radioisotopes. The Argonne program concentrates on nuclear-physic -related problems 6 Bnd includes the determination of the half-lives of Ti(completed) and Fe (in progress), a search for doubly-charged negatiion 1 and development of methods for detecting low concentrations (~t0 )of Ca, which may have applications for dating- in geology and archeology.
The experimental facilities associated with the linac are closeto completion. Currently being- installed are a general-purpose beam line,a beam line for the Purdue superconducting-solenoid electron spectrometer,and diagnostics and protection for the beam-line vacuum system.Improvements and upgrade of present equipment continue. A position-sensitive ionization detector has been installed in the spectrograph withgood mass, charge, energy, and position resolution, while a large-area QE-Edetector and channel-plate detectors have been built for evaporationresidue measurements. A new sophisticated plunger for recoil-distancelifetime measurements has been extensively tested and used in severalexperiments. The ANL-Iowa-Minnesota apparatus for optical-hyperfine-interaction measurements is close to completion. Finally, substantialeffort has been devoted by the research and technical staff towards plansand designs for beam-line layout, experimental equipment, and dataacquisition at ATLAS. The preparation and construction of the ATLASexperimental areas will consume an increasing- fraction of our total effortin 1983-1985.
61
A. HIGH ANGULAR MOMENTUM STATES IN NUCLEI
Our studies have concentrated on and documented several cases ofshape changes which occur at high spin. We have devoted a fair fraction ofour fort on transitional nuclei (Dy and Er isotopes with N ~ 88and Hg) since these are soft with respect to the shape degree of freedomand thus most susceptible to shape changes. We are also interested in thenaty of yrast states at very high spin and have identified statesin Gd with spins in excess of 81/2, the highest recorded spin for anyrast state. Here the level structure and feeding times suggest thepersistence of an oblate coupling scheme up to and slightly above thisspin. Efforts to investigate the structure of continuum states above the
yrast line involve measurements of lifetimes of these states, eitherdirectly or indirectly through the feeding times of yrast states. In theprogram studying the (rh 11 2)n configuration outside Z = 64 and N = 82, along-lived 10+ isomer (w{t half-life corresponding to -0.01 Weisskopfunit) was discovered in 70Yb8 2 , a nucleus very near the proton dripline. This confirms theoretical expectations for the forbidden E2 decay inthe half-filled shell (n = 6); in fact, our data on the (hll/ 2 )n couplingswith n = 3-6 show remarkably good agreement with shell-model calculations.
An active collaboration continues with Prof. P. J. Daly's groupfrom Purdue University. Several projects are also joint ventures with
overseas scientists from Copenhagen, GSI, Jyvskyld', Orsay, and Strasbourg.
a. Gamma-Spectroscopy at Very High Spins in 147 Gd (S. Bjornholm,*J. Borggreen,* J. Pedersen,* G. Sletten,* P. Chowdhury,H. Emling, D. Frekers, R. V. F. Janssens, T. L. Khoo,Y. H. Chung,t and M. Kortelahtit)
One of the striking results of the yrast population experiment
(see section A.g.) was the observation that the yrast states in 14 7Gd were
strongly populated (>80% of ground state strength) even at spin 65/2.
Gamma-gamma coincidence cx:asurements have been performed for
transitions reaching -^6 MeV above the 550-ns isomer at excitation 8.590 MeV
and spin 49/2+. In another experiment angular distributions were measured
and the analyses established spins along- the yrast line up to 79/2 and E ~
17 MeV (Fig II-1); these are the highest values of both spin and excitation
energy observed from yrast states in heavy nuclei. In all experiments an
array of 14 NaI detectors was used to select high multiplicity events which
feed the 550-ns isomer. Consequently, only Y rays feeding- the isomer were
accepted, resulting- in very clean spectra.
*Niels Bohr Institute, Denmark
tPurdue University, W. Lafayette, Indiana.
62
'47GdI Fi 9I vI,
597.4(6)
14795- ----
60
16938
1246 1086(5)
15692300.3 (6)
15177 215.5 3
741.6(8)
14435
1 9 8 6.7(10)
13418 67/2 13448
1 3106 69/2- 1 213$ 7 61208.0 6 2716.3
(3) 896.1 1414.5 ( 2550(9) (I
12210 65/2..)11853 65/2- 11932
976.4 618.6(23) 1.
W
897.9(10)
618.3
(II)
93611234 6V/2- ^ (21)10995 238.9 (42) 1 6 - O.8 nsT10749 246.2 (15) 572 54,3.6(6) 10690 304.5 (56)
10490 259.6(4) 55/21056.1 1808.9 6.3
9693124 638.8 53/2+ 9509372.7(27)49243 t(2) 51/,.12919
8590
1103.4(67)
r
653.0(2)
t
919.1(27)
*
t.,2=550ns
Fig. II-l. Level Scheme of 147Gd on top of the 49/2+ isomer located at
8.59 MeV. Spins and parities have been deduced from angular
distribution measurements.
69/2
65/2
61/2
59/p.-57/2.-
53/2.
4 9/2+t
(3
-- 1
79/ 2
75 /273/27 3/2
q
r9
b
i
i
63
Independent-particle model calculations come out with
configuration assignments in reasonable agreement with the spins and
energies measured, but they also tell us that within a few more units of
angular momentum the nucleus has to find extraordinary ways of producing
the spin, either by exciting nucleons from the next major shell or from
collective rotation.
One way to distinguish between these two modes may be a
determination of subnanosecond lifetimes and feeding times of the upper
states; for this reason Doppler shift measurements with a plunger are
planned.
b. Shape Change in 153Dy (M. Kortelahti,* Y. H. Chung,*P. J. Daly,* Z. W. Grabowski,* A. Pakkanen,* P. Chowdhury,R. V. F. Janssens, and T. L. Khoo)
The yrast configurations of nuclei with N > 90 originate from the
collective rotation of prolate shapes, while those of nuclei with N t 86
arise from the alignment of a few high-j orbitals, leading to oblate
shapes. Our studies of the transitional nucleus 15Dy8 8 have shown the
first instance of a transition from prolate to oblate shapes with
increasing spin (I > 32). 16Dy8 7 should also exhibit a similar shape
transition. Indeed Y-spectroscopic studies through the 12 4Sn (3 4 S,5n)
reaction bear out this expectation, with the oblate shapes emerging for I >41/2. The occurrence of a 2.3-ns isomer with I ~ 47/2 provides strong
evidence for this statement. The study of 1 5 3Dy completes our systematic
investigation of Dy isotopes with N = 82--88, allowing us to trace the
evolution of nuclear shapes as a function of spin and neutron number. In
the process we have observed the important role played by rotational
alignment - induced by the Coriolis force - in shape transitions.
*Purdue University, W. Lafayette, Indiana.
64
c. Lifetime Measuremencs in 15 4Dy (H. Emling,* P. Chowdhury,D. Frekers, R. V. F. Janssens, T. L. Khoo, W. KuYhn,A. Pakkanen* Y. H. Chung,* P. J. Daly,* Z. W. Grabowski,*and M. Kortelahti,*)
We have recently published in Physical Review Letters the results
of extensive Y-ray spectroscopic studies in 16Dy8 8 , which included
lifetime measurements. Levels up to spin 34 or 35 were established, and at
spin 33 a transition from collective to aligned-particle structure was
observed in a heavy nucleus for the first time. The lifetimes suggest that
this transition evolves through a series of triaxial shapes.
The earlier recoil distance lifetime measurements in 15 4Dy had
yielded results with large uncertainties for the yrast states in the spin
region between 10 and 20, owing to the strong influence of slow (10-25 ps)
side-feeding and the fact that the emphasis had been on short lifetimes
(<10 ps).
We have performed new lifetime measurements in 1 5 4 Dy, focussing
on the medium-spin states. A (34S,4n) reaction was used to populate 154Dy
at a lower excitation energy and spin, to enhance the prompt feeding into
the medium-spin range. Recoil-distance techniques were employed with a
newly constructed plunger which fits inside the sum spectrometer. The use
of the sum spectrometer made it possible to obtain very clean spectra for
the 1 54 Dy channel of interest. (A method for isolating a single reaction
channel has been found.)
The results, however, did not significantly improve the accuracy
of the extracted lifetimes, because the feeding times from the non-yrast
continuum states were slow, thereby reducing the sensitivity for measuring
short lifetimes. On the other hand, the observation of this slow component
suggests that the Y-deexcitation pathway goes through single-particle
configurations, before finally feeding into medium-spin yrast states which,
in contrast, are of collective nature. The single-particle configurations
lie above the yrast line and are probably related to the aligned-particle
structures which become yrast around spin 32. Analysis to extract the spin
dependence of the feeding times is currently underway. When completed we
should have important information for a detailed understanding of the
*Purdue University, W. Lafayette, Indiana.
65
structure of the continuum states which lie above the yrast line. We plan
to identify the high-spin yrast structure of 155Ho and to measure lifetimes
here. The coupling of an additional proton to a soft 1 5 4 Dy could lead to
interesting shape changes.
d. Shape Changes at High Spin in 155Er (G. Bastin,t F. Beck,*C. Schick,t D. Frekers, R. V. F. Janssens, T. L. Khoo, W. Kuhn,and M. Kortelahti*)
The occurrence of a shape change at high spin has been
demonstrated in this laboratory for 153,1 5 4 Dy. While up to spin 41/2 and
32+, these nuclei exhibit band structures similar to those observed in the
deformed nuclei, at higher spins the level structure becomes rather
irregular and resembles the one seen in spherical or slightly oblate
nuclei. We made the suggestion that this change is due to the polarization
of the core by the alignment under rotation of nucleons located in high-j
orbitals. In order to test this hypothesis, studies of level structures in
neighboring transitional nuclei are necessary. 155Er was studied with
the 1 2 5 Te( 3 4 S,4n) reaction at 160 MeV and Y-Y coincidences, angular
distributions and an excitation function were measured. The analysis is in
progress.
*Centre de Recherches Nucleaires, Strasbourg, France.
tCentre de Spectrometrie Nucleaire et de Spectrometrie de Masse
du C.N.R.S., Orsay, France.
*Purdue University, W. Lafayette, Indiana.
66
e. Lifetime Measurements of Continuum States in 154,152Er(P. Chowdhury, I. Ahmad,* R. V. F. Janssens, T. L. Khoo,W. Kuhn, G. Rosner, Y. H. Chung,t P. J. Daly,t S R. Faber,tZ. W. Grabowski,t M. Kortelahti,t J McNeill,t A. Pakkanen,tH. Emling,* and D. Ward )
Earlier measurements of the population patterns of the yrast
states in 15Dy86 , together with multiplicity and angular distribution
measurements of continuum Y rays, had yielded evidence suggesting the
presence of collective structures built on high-spin aligned-particle yrast
states in 16'Dy 86 . Direct information on the degree of collectivity can be
obtained from the lifetimes of the continuum states.
We have employed a Doppler-shift attenuation method to measure
continuum lifetimes in the Er86 and 8Er8 4 nuclei, using (6 4Ni,4n)
reactions. Continuum spectra were compared for the case where the residues
were allowed to recoil into vacuum (vrecoil ~ 0.04 c), and stopped in a Au
backing (~1.5 ps stopping times). Two 25 x 30 cm NaI crystals were gain-
stabilized and used with 10-cm diameter central Pb collimators, in
conjunction with a sum spectrometer and a Ge(Li) detector.
The use of Au stopping foils has eliminated severe normalization
problems previously encountered with Pb stopping foils, which tend to be
easily contaminated with light element impurities. The recent data are
currently being analyzed. A preliminary analysis of the 15 4Er data
suggests lifetimes consistent with a high degree of collectivity in the
continuum cascades. The lifetimes of statistical y rays with 2 MeV ( EY <
4 MeV are also of interest, in light of recent results which suggest long
decay times ('2 ps) for these y rays in 152Er. A more complete analysis is
necessary to extract the lifetimes of the statistical transitions.
*Chemistry Division, ANL.
tPurdue University, W. Lafayette, Indiana.
*GSI, Darmstadt, W. Germany.
Chalk River Nuclear Laboratories, Chalk River, Ontario, Canada.
67
f. Measurement of Feeding Times in 152Dy (H. Emling,P. Chowdhury, Y. H. Chung,* P. J. Daly,* D. Frekers,Z. W. Grabowski,* R. V. F. Janssens, T. L. Khoo,M. Kortelahti,W KuYhn, and A. Pakkanen*)
The structure of states above the yrast line can be directly
probed by a measurement of the feeding times of the yrast states. To that
effect, we have made recoil-distance measurements of feeding times for
yrast states in 1 52 Dy with a (3 4 S,4n) reaction, using a newly constructed
plunger which fits inside the sum spectrometer. This allows a study of the
feeding times as a function of sum energy, and hence as a function of
initial angular momentum. Analysis of the data is in progress.
*Purdue University, W. Lafayette, Indiana.
g. Yrast Population Patterns in a Wide Range of Nuclei(J. Borggreen,* G. Sletten,* R. V. F. Janssens, P. Chowdhury,T. L. Khoo, Y. H. Chung,t P. J. Daly,t Z. Grabowski,tand M. Kortelahtit)
The purpose of this experiment is to investigate the dependence
on nuclear structure of the relative population of states on the yrast
line. We have studied the population-pattern as a function of spin in the
nuclei 148--1 56Dy, 154-- 16 0Er, 14 6,14 7Gd. The nuclei were populated
in 345- and 30 Si-induced reactions at beam energies chosen such that all
compound nuclei were obtained with similar angular momenta and excitation
energies. The analysis of the data has been completed. Striking
differences have been observed between the feeding patterns in the light
and heavy isotopes, in particular for the Dy isotopes. Indeed, -100% of
the Y-ray flux is measured along the yrast line up to the state having a
spin corresponding to the largest value that can be obtained from the
alignment of the valence nucleons on the symmetry axis (146Gd being
regarded as a core). This was observed for the nuclei 148,150,151,152Dy
which are known to have a slight oblate deformation. In contrast, in the
well-deformed prolate 154,155,156Dy nuclei, the intensity along the yrast
*Niels Bohr Institute, Copenhagen, Denmark.
tPurdue University, W. Lafayette, Indiana.
68
line drops gradually starting from the lowest spin states. These findings
are correlated with the nuclear structure, the level density in the
vicinity of the yrast line and with the Y decay properties of the states
populated. Calculations are currently underway by S. Aberg (Nordita).
Preliminary results indicate that the main experimental trends can be
accounted for with level densities obtained from the deformed independent-
particle model.
h. The (ih 11 1?)6 Spectrum in 1 Yb?(Y. H. Chung,* P. J. Daly,*
Z. W. Grabowski,* M. Kortelahti,* J. McNeill,* P. Chowdhury,R. V. F. Janssens, T L. Khoo, R. D. Lawson, and H. Emling)
In continuation of our systematic study of N = 82 nuclei above
the N = 82 and Z = 64 doubly closed shells, we have investigated the
nucleus 9Yb82. Shell-model calculations, using 6 Gd8 2 as a closed core,648
have been extremely successful in describing the (h 1 1/2)6 level structure
in the 3, 4 and 5 proton nuclei 14911, 15 0Er and 1ilTm, respectively.in67 68 69 pciey
A 9 6 Ru( 5 8 Ni,2p) 1 5 2 Yb reaction was employed in conjunction with a
newly installed beam deflector system, which was used to pulce the beam. A
40's 10+ isomer was found. Both the halflife (^O.01 Weisskopf unit) of the
10+ state and the transitions below the 10+ isomer are in excellent
agreement with theory. The 10+ + 8+ decay is forbidden in the half-filled
hll / 2 proton shell and hence is expected to have a long lifetime for E2
decay. An alternative decay of the 10+ involves a 10+ + 7~ E3
transition. The experimentally observed decay of the 10+ is seen to
proceed strongly through the 7~, 5~, and 3 states to the 0+ state, as
expected from the theoretical calculations.
*Purdue University, W. Lafayette, Indiana.
69
i. Spectroscopy of 10 0Cd (L. Clemann,* M. Barclay,*D. Cacic,* W. C. Ma,* C. Maguire,* J. Hamilton,* D. Frekers,R. V. F. Janssens, and T. L. Khoo,
By taking advantage of the fact that heavy-ion reactions can be
used to produce nuclei far from stability, the reaction 4 6 Ti( 5 8 Ni,2p2n) has
been used to study the spectrum of the very neutron-deficient nucleus
10 0Cd. 1000d in its ground state has a g7/2 neutron pair and a proton hole
outside the N = 50 closed shell and it is expected that these
configurations will have a considerable influence on the yrast spectrum.
The spectroscopy of Cd isotopes with larger neutron number is reasonably
well known, and information on 100Cd will make it possible to trace the
evolution o' different shapes as the neutron number increases from the
closed shell N = 50. In the experiment we used the technique of Y - Y
coincidences in conjunction with the sum spectrometer to identify
transitions in 1 0 Cd. The analysis of the data is in progress.
*Vanderbilt University, Nashville, Tennessee.
j. Prolate and Oblate Rotational Bands in 186Hg(R. V. F. Janssens, D. Frekers, P. Chowdhury, H. Emling,T. L. Khoo, W. Ku'hn, Y. H. Chung,* P. J. Daly,* Z. Grabowski,*
and M. Kortelahti*)
The light Hg isotopes are located in a transitional region
between spherical or slightly oblate nuclei and the well-deformed prolate
rare earth nuclei. Evidence for shape coexistence has been reported for
the light even-even Hg isotopes (i.e., A = 188--184). These nuclei have a
small oblate ground-state deformation as well as a prolate minimum located
slightly higher in energy ('500 keV). The present study aims at
investigating the properties of the bands located in both minima. 18 6Hg
was extensively studied this year with the 1 56Gd (3 4S,4n) reaction at 165
MeV though Y-Y coincidence, angular distribution and excitation function
measurements. A level scheme (Fig. 11-2) has been deduced which shows the
following main features: (i) the ground band is seen up to 6+ and probably
8+, (ii) the rotational band built on the prolate deformation is
*Purdue University, W. Lafayette, Indiana.
70
2
5115.8 20
[5.9] 666.8
4448,9, 8f
[9.6]I 636.6
3812.3 16+
[10.1]I 611.0
[25.0]I
2619.7
2251.7
[2.7] 575.1
1
[33.9]
[57.5]
3
5347.5 (22+)
[6.2] 572.3
4775.2 20+
[I1.0] 506.9
4268.3,
[13.7]3827.3
[~ 15]3470.6,
[16.6]
3088.8[i !.I]
581.6 2833.3
12+
542.0
10+
488.9 '(0)
1588.8, 8
596.1 [73.3] 424.2
(4+) 1164.6,6+
~81] 356.7
675.2 879 4
p 620.7 2+
,2+ 522 0+
405.3 Hg86H080 106
I8*
441.0I6+
356.7_14+
381.8
12+255.5
10
(
Fig. 11-2. Level scheme of 186Hg.
[~5].1080.5,,
405.3
[100]0
I
[8.5]|
identified up to 20+ and shows a gentle upbending between levels with spin
14+ and 18+, (iii) a new band is seen from 10+ to 22+. It crosses the
band discussed in (ii) at I7 = 16+ without any apparent interaction. This
band feeds the prolate band at 10+ and shows also an irregularity in the
energy spacings between the 12+ and 14+ levels.
Calculations in the framework of the Cranked Shell Model have
been performed by S. Frauendorf and Z. Y. Zhang (University of
Tennessee). The upbend described in (ii) is explained by the crossing of
the prolate groundband by an aligned 11 3 /2 neutron band. The interaction
between the bands is strong and, hence, only an upbending is predicted, in
agreement with the data. The computed critical frequency and the gain in
alignment resulting from the interaction are in good agreement with the
experiment. The same calculations also account for the behavior of the new
band. Here again i1 3 / 2 neutrons are playing a major role but the motion
takes place in the oblate minimum. In particular, the absence of
interaction and the difference between the energy spacings in the two bands
are well accounted for. These data represent the first case where the
decoupling of 11 3 /2 neutrons is observed simultaneously for two different
deformations. Further confirmation of this interpretation will be provided
by an investigation of the odd-even isotopes 185,18 7 Hg which is planned for
next year. A 80-us isomer was also observed in 1 8 6 Hg. The analysis of its
decay is currently underway.
73
B. FUSION OF HEAVY IONS
The availability of high-quality beams with masses A >,60 andwith energies sufficient to overcome the Coulomb barrier for even theheaviest targets, has resulted in increased study of the fusion process insuck heavy systems. These efforts represent a natural extension ofprevious work with lighter projectiles that has been done in past yearswith the tandem accelerator. Of particular interest is whether nuclearstructure effects are observed in the fusion of two such heavy ions, aswell as the detailed nature of the fusion dynamics near and above thefusion barrier. A recently developed electrostatic-deflector system hasbeen used to separate evaporation residues near 0* from the beamparticles. Nuclei far from the line of stability have been produced andtheir delayed a activity has been studied after implantation in a surface-barrier detector. In addition, the average atomic charge states ofevaporation residues have been measured using this deflector system. Whencoupled with the delayed-alpha-activity measurements we can now study theprobability for compound nuclear survival with cross sections in the micro-barn region.
To gain information on the relaxation dynamics following theinitial contact of two fusing ions (for which there exists little data) wehave measured neutron spectra and neutron multiplicity distributions incold fusion reactions. Comparison with statistical-model calculationssuggest that there is a suppression of neutron emission. This may possiblybe related to trapping in a superdeformed well as the highly deformedinitial state relaxes to the equilibrium shape.
a. Fusion of 64Ni + 1 1 2 ,1 14 ,116,118,1 2 0 ,1 2 2 ,1 2 4Sn (W. S. Freeman,H. Ernst, D. F. Geesaman, W. Henning, W. KuYhn, F. W. Prosser,*J. P. Schiffer, and B. Zeidman)
Detailed measurements of evaporation residue yields following
fusion reactions for the 64Ni + Sn system have been obtained. Excitation
functions for 6 4Ni ions incident on the even-mass Sn isotopes were measured
over the energy range 235 < Elab < 310 MeV. (See Fig. 11-3.) An
electrostatic deflector placed after the target was used to separate the
evaporation residues emerging from the target near Blab = 00 from the
intense flux of beam particles. An improved detector allowed measurements
of angular distributions at up to four angles in a plane perpendicular to
the deflection plane. When combined with our previous measurements using5 8Ni projectiles on the same Sn isotopes, the compound nuclei produced
varied in neutron number by 18 neutrons, a change of 20%. We find that the
maximum yields for all compound nuclei occur near 170--180 MeV (c.m.) with
*University of Kansas, Lawrence, Kansas.
00
I0
0.I
- I III I 1 1
5Ni + Sn
-5 A-S
-Ow
~ Iv
~ j
-1
150 160 170 180 190 200 210 150E(MeV)
c.m.
- I I I I I I I -
- 84 AN Ni+ Sn
--- O-0--
-o
I o " 124o122.1204/C o118 A318 Sn _
"116
" I 112
I I I I I
160 170 180 190 200 210
even-mass Sn isotopesFig. 11-3. Evaporation residue cross sections for 58,64Ni fusing with the(A = 112-124). Lines are drawn only to guide the eye.
E
bv
'
I, , t1 i .
T
75
the maximum cross sections increasing by about one order of magnitude
from 58Ni + 114Sn to 64Ni + 124Sn. (See Fig. 11-4.) These results allow a
systematic study of compound nucleus survivability in systems for which
fission competition becomes increasingly important. Related topics of
current interest include possible entrance channel effects and whether an
"extra-push" energy is needed to achieve fusion in such heavy systems. To
further understand the fusion process, we plan to extend our study of the
64Ni + Sn system by measuring fission excitation functions over the same
energy range.
b. Fusion of 58Ni + 112,114,116,118,120,122, 1 2 4Sn (W. S. Freeman,H. Ernst, D. F. Geesaman, W. Henning, T. J. Humanic, W. Kuhn,F. W. Prosser,* J. P. Schiffer, and B. Zeidman)
We have measured, at selected energies, the angular distributions
of the evaporation residue yield from the fusion of 58Ni with the even-mass
Sn isotopes using our improved AE-E detector assembly and electrostatic
deflector. These measurements allowed us to fix the absolute
normalizations of our more extensive Blab = 00 excitation function which we
had obtained with our earlier, single AE-E counter. As a result, we were
able to compare excitation functions leading to the same compound nucleus
for 5 8Ni + 12 4Sn and 64Ni + 118Sn. The excitation functions for the two
entrance channels have similar shapes with the 6 4Ni + "18Sn data having
slightly large cross sections above the barrier. The implications
regarding the statistical model and possible entrance-channels effects are
currently being assessed.
*University of Kansas, Lawrence, Kansas.
c. Fission of 64Ni + 112,114,116,118,120,122,124Sn(W. S. Freeman, D. F. Geesaman, W. KuYhn, G. Rosner,J. P. Schiffer, and B. Zeidman)
We have recently begun a series of measurements of the fission
yields from 64Ni + Sn. These results, when combined with our evaporation
residue (ER) cross section measurements for the same systems, will give
information on the complete fusion (fission + ER) cross sections near and
above the classical fusion barrier. Of particular interest is whether the
76
' I ' I ' 1 ' 1 ' I inuh1EI
64o Ni + Sn
200 - 58" Ni+Sn
180MeV (c.m.)
I50-
Eo:
bw100
50
170 174 178 182 186 190Ac4 CN.
rig. 11-4. Values of aER as a function of the compound nucleus mass for5 8,6 4Ni+Sn at E = 180 MeV. The open (filled) circles denote6 4Ni(5 8Ni) as t m projectile. The solid (broken)-line histo rramsare the results of statistical-model calculations with 6 4Ni( 8Ni) asthe projectile.
77
observed target (or compound nucleus) mass dependence of the ER cross
sections above the barrier reflect differences in the fusion cross sections
or differences in the fission competition. To date, one experiment has
been performed at incident energies of Elab = 275 and 320 MeV for which the
data analysis is in progress.
d. Delayed Alpha-Decay of Evaporation Residues Formedin Fusion Reactions (W. S. Freeman, D. F. Geesaman,W. Henning, W. Kuhn, G. Rosner and B. Zeidman)
Delayed alpha decays of the evaporation residues formed following
the complete fusion of two heavy ions were observed after their
implantation in silicon surface-barrier detectors placed near 0lab = 00.
The electrostatic-deflector system used in our fusion cross-section
measurements was utilized to separate the evaporation residues from the
beam. Measurement of the delayed alpha energies and lifetimes provides a
powerful additional means of particle identification and allows the
measurement of lower evaporation residue cross sections. To ascertain the
sensitivity of this technique with our present experimental configuration,
we searched for delayed activity using 5 8Ni and 3 7C1 beams bombarding
several targets spanning a broad mass range. The heaviest target-
projectile combination for which we observed delayed alpha activity
was 37C1 + 17 1Yb which forms the compound nucleus 208Fr. These results
showed background contributions in the ac-particle spectrum at a cross-
section level of ~2 b, two orders of magnitude better than our sensitivity
using the standard AE-E method. Additionally, c-decay measurements have
been made following the fusion of 5 8Ni + 1 1 2 ,114Sn which form the proton-
rich compound nuclei 1 70 ,17 2 Pt. These nuclei are in a region where there
is little information with regard to masses or lifetimes. The data are
presently being analyzed.
78
1.0
1.5
6 8
/ELABq
2.0
10
(M:V)
12
2.5
14
3.0
16
FIELD STRENGTH (kV/cm)
Fig. 11-5. The relative evaporation residue yield for 58Ni + 4,124Sn
as a function of the deflector electric field strength (lower scale) and
the average energy-to-charge state ratio (upper scale for EM = 281 MeV.
0
1-
wi
I I
I
+opsf
j/ "58N +124S
10 58Ni+ 1 Sn
I1 i
I I I I
0.5
1
I | I I
79
e. Atomic Charge States of Evaporation Residues (W. S. Freeman,D. F. Geesaman, W. Henning, W. Ku'hn, F. W. Prosser,*J. P. Schiffer, and B. Zeidman)
In the course of our measurements of evaporation residues formed
in heavy-ion fusion reactions (e.g. Ni + Sn), we have employed an
electrostatic deflector after the target to separate the low-energy,
highly-charged fusion products from the beam. The deflector separates
particles according to their charge-to-energy ratio. A knowledge of the
average energy of the evaporation residues, which is set by the kinematics
of the fusion reaction, together with the known experimental geometry then
enables a determination of the average atomic charge state. (See
Fig. 11-5.) We find charge states for Ni + Sn fusion products that are 6--
13 units higher than the equilibrium value expected for stripping in the
target (at E{a(Ni) - 280 MeV). This suggests that nuclear decays after
the target foil (e.g. internal conversion and Auger electrons) play an
important role. As has been previously realized, these anomalously high
charge states have potential implications for fusion measurements that
employ recoil mass spectrometers or velocity filters with additional
focussing elements that are sensitive to the atomic charge state.
We plan to extend our fusion cross-section measurements, using
the deflector, to heavier systems. As a byproduct, these measurements will
also provide additional information on the average atomic charge states of
these heavier evaporation residues.
*University of Kansas, Lawrence, Kansas.
f. Prompt Compound-Nuclear K X-rays in Fusion Reactions Inducedby a Heavy Projectile (H. Ernst, W. Henning, C. N. Davids,W. S. Freeman, T. J. Humanic, M. Paul,* and S. J. Sanderst)
The limits of complete fusion and compound-nucleus formation in a
nuclear reaction induced by a heavy projectile are currently of great
interest. We have studied prompt K X-rays in compound-nuclear reactions
induced by a heavy projectile, by determining total production cross
*Hebrew University, Jerusalem, Israel.
tYale University, New Haven, Connecticut.
80
sections and multiplicities of K X-rays for the systems 32 + 116,120,124Sn
from X-ray singles, X-ray--X-ray coincidences, and direct evaporation
residue yields over the incident energy range 130 MeV < Elab < 202 MeV. We
find a slow dependence of the multiplicities and cross sections on target
mass and incident energy, establishing the prompt K X-ray yields as a
reliable indicator of the complete fusion cross section behavior induced by
a heavy projectile in this mass region. This work has been recently
completed and published in Physics Letters.
g. Suppression of Neutron Emission in 'Cold' Heavy-Ion Fusion(W. Kuhn, P. Chowdhury, R. V. F. Janssens, T. L. Khoo,F. Haas,* J. Kasagi,* and R. M. Ronningen*)
In "cold" heavy-ion fusion reactions, where the excitation energy
is low (E* < 50 MeV), the relaxation of the initially highly-deformed
nucleus may be influenced by shell effects. For example, the system may be
trapped in a secondary minimum in the potential energy surface
corresponding to a larger deformation than normally observed near the
ground state. We have studied the system 64Ni + 92Zr, forming the compound
system 156Er with E* = 46 MeV. Measurements have been made of the relative
yields of the neutron-emission channels (Fig. 11-6) and of the neutron
spectra corresponding to different Y-sum energies (Fig. 11-7). When
compared with the results of statistical model calculations, with
parameters constrained to fit all available data, the experimental 2n/3n
ratio is ~ 38 times larger. Thus there seems to be a suppression of
neutron emission. One possible reason for this is that there is trapping
in a potential well, as described above, for a time longer than that for
neutron emission. The available energy for neutron emission is then
reduced, leading to the emission of fewer neutrons than might otherwise
have been expected.
If this speculation is correct, there are several consequences
which can be experimentally observed, e.g. in the energy distribution of
the continuum Y-ray spectrum. Future experiments will be directed towards
the search for the evidence necessary to confirm the suggestion of
deformation traps.
*Michigan State University, East Lansing, Michigan.
81
* 50
L
> 10-j 5
I 2 3 4NEUTRON MULTIPLICITY
Fig. 11-6. Comparison of experimental (open circles) neutron
multiplicity distribution with those from statistical-modelcalculations using the normal (solid bars) and elevated (dashed bars)
yrast lines.
82
6I0
-C
"
0
4I0
Siv
510
zOIo
-I
0
w)
L>u
He
2.5
2.0
1.5)
2
10
4 6C.M.- ENERGY (MeV)
20SPIN
30
8
40(i)
Fig. II-7. (a) Neutron spectra, measured at 00, for six different gamma-raysum energy slices. The straight lines represent fits with an exponential
function. Deviations from the exponential shape at high sum energy aredue to contamination from isomeric gamma rays. (b) Temperatures, derivedfrom the fits in (a), as a function of mean entry line spin corresponding
to the different sum slices. The solid line represents results fromCASCADE calculations, using an yrast line elevated %10 MeV with respectto the known one.
HIGH SUM ENERGY (a)
TLOW SUM ENERGY
10
- -I
. (b .
AOM4,
83
C. REACTION MECHANISMS AND DISTRIBUTION OF REACTION STRENGTHS
Studies of reaction mechanisms and distribution of reactionstrengths have continued to be extended to higher energies, heavierprojectiles, and heavier target nuclei as the accelerator capability hasincreased. Transitions to distinct final states produced in reactionsinduces 7by both lighter projectiles (e.g. 0) and heavier projectiles(e.g. Cl) have been studied to better understand the energy andprojectile dependence of direct processes and the transition fromquasielastic to strongly-damped processes. Velocity spectra ofindividually-resolved evaporation residue-like masses have been used inboth singles and coincidence measurements to obtain evidence of significantcross sections for incomplete fusion processes at higher bombardingenergies for some projectile-target systems.
a. Rgacti s to Resolved States and Nonfusion Channels for0 + Ca at Elab = 158.2 MeV (T. J. Humanic, H. Ernst,
W. Henning, and B. Zeidman)
Elastic scattering, inelastic scattering and single-nucleon
transfer cross sections to resolved states were measured for the 160 + 4 8Ca
system at Elab = 158.2 MeV. In addition the total nonfusion reaction cross
section was determined. This study is part of an investigation of energy
dependence of the reaction cross sections in the 160 + 48Ca systems and a
test of the DWBA model as well as other reaction models. Qualitative
agreement between the experimental results and DWBA predictions was found
for a number of resolved states. The results have been published in
Physical Review.
b. Elastic Sca ering4 nd Single-N leon Transfer ReactionsInduced by 60 on Ca at lab( 0) = 150 MeV (G. Stephans,D. G. Kovar, H. Ikezoe, J. Kol a;,R.-Pardo, K. E. Rehm,G. Rosner, and R. Vojtech*)
Angular distributions for elastic and inelastic scattering, and
for the single-nucleon transfer reactions (160,150), (160,1 5N), (160,170),
and (160,1 7F) to low-lying states of the projectile- and target-like
ejectiles have been measured at Elab(1 60) = 150 MeV using the split-pole
magnetic spectrograph. Using beams from the tandem--linac accelerator,
energy resolutions of "175 keV were obtained. Similar data have been
*University of Notre Dame, Notre Dame, Indiana.
84
I I I I I I I I I I I * I I I I I I I I 140 640 16
Ca + 0
TRANSFER REACTIONS
17 39c Og.s.+ Ca g.s.17 39 -
o 17Fg.s.+ K g.s. _
15 41o Ng.s.+ Scg.s. -
15 41-x Og.s.+ Cag.s.
--.------ Avg.= 0.99 -
O-
000
X
_ X
a . I I * a a a I I II I a I a I50 75 100 125
EIb( 0)
1
150 175
Fig. 11-8. Ratio of integrated DWBA cross sections to experimental crosssections for all single-nucleon transfers to projectile-target ground
states are plotted versus 160 bombarding energy. Results for 56 and75 MeV are from Ref. 1 and for 150 MeV are from the present study.
2.0-
I.5-
0 I.OH
O.5
'
I I l l 1 l l l l
I
85
obtained at lower energies1 and the present data play an important role in
establishing the cross-section behavior as a function of bombarding
energy. For the elastic and inelastic scattering of interest is the
apparent increasing importance of the inelastic excitation of the
projectile and questions regarding the importance of coupled-channel
effects. For the transfer reactions the interest is in how well DWBA
(CCBA) calculations reproduce the energy dependence of the cross sections
at bombarding energies significantly above the Coulomb barrier. The data
have been analyzed and compared with preliminary DWBA calculations. How
well DWBA predicts the cross section behavior is shown in Fig. 11-8 when
the ratios of integrated DWBA cross sections to experimental cross sections
for all single-nucleon transfers linking to projectile-target ground states
are plotted. The trend toward overprediction by the DWBA, which was
indicated by the lower energy data, is not seen in our preliminary analysis
of the higher-energy data of the present study. This result differs from
that found for 160 or 208Pb, when a roughly monotonic trend of
underprediction at low bombarding energies and overprediction at higher
energies was reported.2 However, the present, work is similar to the
analysis of 160 on 4 8 Ca, where the a(DWBA)/a(exp) ratio was found to be
essentially identical at 56 and 158.2 MeV beam energies.3 Future studies
of the increasing importance of inelastic scattering and transfer reactions
to unbound states of the projectile-like ejectiles and the projectile
dependence of direct reaction processes involving heavier projectiles are
being planned.
'E. Rehm et al., Phys. Rev. C 25, 1915 (1982); D. Kovar et al., Bull.
Am. Phys. Soc. 22, 564 (1978); C. Olmer et al., Bull. Am. Phys. Soc. 23,
941 (1978).
2S. C. Pieper et al., Phys. Rev. C 18, 180 (1978); C. Olmer et al.,
Phys. Rev. C 18, 205 (1978).
3T. J. Humanic et al., Phys. Rev. C 26, 993 (1982).
86
c. Measurements of Evaporation Residues Produced in 160 + 2 4Mg at4 -Elan( 0) < 9.5 MeV/A (D. G. Kovar, R. R. Betts,*P. Chowdhury, D. Henderson,* T. J. Humanic, H. Ikezoe,R. V. F. Janssens, W. Kuhn, G. Rosner, B. Wilkins,*and K. L. Wolf*)
Time-of-flight singles measurements resolving the individual
masses of the evaporation residues were performed at Elab(160) = 59.5 MeV
to complete measurements begun last year.I Results of these measurements
showed that the centroids of the velocity spectra of evaporation residues
at 59.5 MeV are consistent with that expected for complete fusion, whereas
those at 100 MeV and 150 MeV showed deviations of ^2% and 5%,
respectively. Comparisons of the predictions of the evaporation code
LOLITA with the experimental results indicate that at Elab(160) = 59.5
MeV. The velocity spectra, angular distributions, and to a somewhat lesser
degree the mass distribution are well reproduced. At Elab = 150 MeV the
centroids of the velocity spectra ,f evaporation residues are poorly
reproduced and if one performs a detailed comparison as function of angle
only ^-600 mb of the X950 mb of evaporation residue-like cross section is
consistent with complete fusion. A coincidence measurement of individual
mass residues with protons and alphas was performed at Elab(1 60) = 150 MeV
in an attempt to distinguish more quantitatively the contributions of
incomplete fusion processes by observations of energetic protons and alphas
which are inconsistent with statistical evaporation. The results of
measurements at four angles (230, -8*, -18 , and -28*) for light-particles
and one angle (0 lab = 80) for the residue have been analyzed. Shown in
Fig. 11-9 are the alpha-particle velocity spectra (9L = -18*) observed in
coincidence with the various final particle masses detected at = 80.
Evidence for high energy (e.g., beam velocity) protons and alphas is
clearly observed in the measurements and comparisons with model predictions
for complete fusion are being made at the present time. Pending the
results of the analysis, a program of measurements to distinguish
incomplete and complete fusion processes via coincidence measurements may
be indicated. Such information would be of interest since at the present
time quantitative cross sections for incomplete and complete fusion cross
sections at higher energies are almost nonexistent.
*Chemistry Division, ANL.
1T. Humanic et al., Bull. Am. Phys. Soc. 27, 478 (1982).
87
" """ N M " .o sol """"S."+ .. "N " " ""so" " " " "g. r" " 4 " " ".
" N .u* w " *i " ..w M NU " "
" "g" I is " rn. " M " N ". N.
.S ..mr 494 nm.of owa s 40* .N Nto. " "
." "" ..."+ oM"+" o" " ""
" o " "" 0401 «m "yM, 04, "", N m " "*
""" eve0n. ~ memm .
.j4 IeemmA "e5"N" " " one M
-"""N * 1 w"p "" M """" .
160 +24M
E =150MeVlab&HI 8
& (~80
3 5Va (cm/ns)
7 9
Fig. 11-9. Velocity spectrum of alpha particles (0 - -18*) detected
in coincidence with the various mass heavy-ion products observed at
0HI - 8*.
38
34-
30
26
22
18
14
l0l-
U)
U)
w0nU)LU:
6
21 1
'II
'II
'I |
I I I II I I.I
I
88
d. Tim of-Flight Measurements of Evaporation Residues Producedin Si-Induced Reactions (G. Rosner, D. G. Kovar,P. Chowdhurv D. Henderson,* H. Ikezoe, R. Janssens, W. KuYhn,G. Stephans, B. Wilkins,* J. Hinnefeld,t J. Kolata,tand F. Prosser, Jr.*)
Angular distributions of velocity cross sections 1/v2 d2 a/d \dR of
fusion evaporation residues (ER) were measured for 1 60(ELab = 150 MeV)
and 2 8Si (Eab = 175, 214, 219, and 263 MeV) induced reactions on targets
of 12C, 24Mg, 2 7A1 28Si and 40Ca. The reaction products were identified
by mass (cm ~ Et2) using 2 channel-plate detectors (start,stop) and a
surface barrier detector (stop,E). A typical velocity versus mass spectrum
is shown in Fig. II-10.
Previous studies suggest that for asymmetric systems (light
projectile, heavier target) incomplete fusion or incomplete momentum
transfer occurs at Elab/A >, 5 MeV. The average ER velocities have been
reported to be appreciably smaller than the velocity of the center-of-
mass. The intention of the present set of experiments was to study in more
detail the projectile-target dependence of this behavior and to single out
entrance channel effects by forming the same compound nucleus 56Ni via 160
+ 40Ca and 28Si + 28Si. It is found that the tota,ER cross sections
for 28Si + 2 8Si are significantly smaller than those for 160 + 40Ca at
comparable center-of-mass energies. While the velocity spectra observed
for 2 8Si + 28Si are in good agreement with the predictions of complete
fusion calculations (LILITA), those for 160 + 40Ca show significant
discrepancies. Both observations indicate that ER formation in 2 8Si + 28i
is essentially due to complete fusion at the bombarding energies measured,
while the excess of ER cross sections in 160 + 'Ca stems from incomplete
fusion processes. A comparison with ER velocity cross sections for the
other fusion reactions measured is underway.
*Chemistry Division, ANL.
tUniversity of Notre Dame, Notre Dame, Indiana.
*University of Kansas, Lawrence, Kansas.
89
-- ATT!II! 2 8 Si +
40
36 40"32
27AlI
8 b
la
E = 219 MeVla b
J
V
28
. I I I
2800I I . I
3600I I I I
Et (arbitrary units)
I I I
4400I
5200
Fig. II-10. Velocity versus mass spectrum of the reaction 219 MeV28Si + 27A1 - ER + x, measured at Elab = 5*. The fusion evaporationresidues (ER) are centered around mass 44 amu.
i"
.:-
--"
3.6
3.2
2.8
2.41-
2.0
1 .61-
(0
EV
-
-JLi
0.8
O.4- MASS(amu)
vJ
2000
Tom'1
44
1
90
e. Fusion Cross Section Measuren.ents for 2 0 Ne + 4 Ca at
E lah(2Ne) = 150 and 220 MeV (D. G. Kovar, W. Bohne,*M. Burgel,* Ch. Egelhaaf,* H. Fuchs,* A. Gamp,* K. Grabisch,*H. Homeyer,* H. Morgenstern,* and W. Rauch*)
At the present time large uncertainties exist regarding the
experimental cross sections for complete fusion at energies Elab > 7 MeV/A
because of the presence of incomplete fusion processes. Time-of-flight
(TOF) measurements resolving the individual masses allow inspection of the
velocity spectra of the eva oration residue-like fragments. For the 20Ne
+ 4 0Ca system at Elab(2 0Ne) = 291 MeV the velocity spectra revealed
centroids significantly smaller (~10%) than that expected for complete
fusion (i.e., complete momentum transfer), suggesting the presence of
contributions from incomplete fusion and providing an indication of their
magnitude.1 In the present study TOF measurements were performed for
the 2 0 Ne + 4 0Ca reaction at Ela5 ( 2 0 Ne) = 150 and 220 MeV to establish the
systematics of the departure of the centroids of the evaporation residue
velocity spectra from that of full momentum transfer a as function of
bombarding energy and to attempt to establish the cross sections for
complete and incomplete fusion. The experiments were performed at the
VICKSI facility at the Hahn Meitner Institut, Berlin, where the
measurements provided unambiguous mass resolutions for the heaviest
residues detected (m < 54 amu). The analysis of the data is underway at
this time. Plans for the future involve extension of these measurements to
higher energies (15 < Elab ' 35 MeV/A) to explore the use of velocity
spectra as an observable for distinguishing complete and incomplete fusion
processes.
*Hahn Meitner Institut, Berlin, Germany.
1H. Morgenstern et al., Phys. Lett. 113B, 463 (1982).
91
f. Study of Direct Reactions in the System 37C1 + 208Pbat Elab = 250 MeV (K. E. Rehm, W. Kutschera, and M. Paul*)
In order to investigate the transition from quasielastic to deep
inelastic reactions we are studying the interaction between different
projectiles and 208Pb at energies not too high above the Coulomb barrier.
In a first experiment we investigated the system 37 C1 + 2 08Pb. With an
energy resolution of ^450 keV it was possible to measure the angular
distributions of elastic scattering and for the excitation of the first
excited states in 3 7Cl(l/2+) and 20 8Pb(3~). The results are shown in
Fig. 1I-11. The solid lines represent optical-model (elastic) and DWBA
(inelastic) calculations performed with the code PTOLEMY.1 From the least-
squares fit to the angular distribution for elastic scattering the
following optical potential parameters are obtained: -V = 13.1 MeV, r0 =
1.3 fm, a = 0.645 fm, -W = 5.5 MeV, r0' = 1.446 fi, a' = 0.223 fm. For the
DWBA calculations no parameters have been adjusted. The B(EL) values were
taken from the literature and the same mass and charge deformation lengths
have been used. The transfer reactions are strongly dominated by the
neutron pickup channels (37Cl,3 8C1) and (3 7C1,3 9C1), whereas deep inelastic
scattering reactions are observed mainly in the proton transfer channels
(37C1,S), (3 7 C1,P) and (3 7 C1,Al).
*Hebrew University, Jerusalem, Israel.
1M. H. Macfarlane and S. C. Pieper, ANL Report ANL-76-l1, Rev. 1.
g. Spectroscopic Studies of 2 3 4Th with the (180,160) Reaction(K. E. Rehm, D. Frekers, T. Humanic, R. V. F. Janssens,T. L. Khoo, and W. Kutschera)
The ground-state rotational band of 2 34Th has been investigated
with particle-Y techniques using the split pole magnetic spectrograph.
Outgoing particles from the reaction 180 + 2 32Th at Elab - 130 MeV were
momentum analyzed in the spectrograph at a solid angle of 5.6 mar and
detected by the position-sensitive AE-E ionization chamber in the focal
plane. Ray-tracing techniques were used to correct the AE and Be
signals. Gamma rays coincident to different particle groups in the
outgoing channel were detected in an 80-cm3 or cc GeLi detector, positioned
92
I I I I I
371C+ oePb
- EOb=250MeV
ELASTIC
- Cl (1/2+)E =I.727 MeV1
2)0 8 Pb (Y)
Ex= 2.615MeV
I I I I I I
300 40 50* 600 700 800
Bc.m.
Fig. II--11. Angular distributions for elastic scattering and inelasticexcitation of the 1/2+ state in 3 7 C1 and the 3~ state in 208Pb,respectively, as measured in the system 3 7C1 + 20 8Pb at Elab = 250 MeV.
b
b
0.I
'!)
E
C;
b-O10
'
I
I
93
827.4
556.9
333.1
162.12
49.37-0
2 3 2 Th
10+ (851.7)
8+ 567.6
6+ 338.3
4+.
20+
Fig. 11-12. Energy levels for 232Th and 234Th.
163.9
49.40
2 3 4 T h
94
10 cm from the target. Previously only the 2+ state in 2 34Th has been
unambiguously identified. In our experiment states up to I = 8(10) could
be observed (see Fig. 11-12). An attempt to increase the momentum transfer
using the (170,150) reaction was not successful. In future experiments we
plan to replace the GeLi detector with an electron spectrometer for higher
detection efficiency.
h. Large Neutron-Transfi Cross Sections Observed in 5 8Ni and 4 8TiInduced Reaction on Pb (K. E. Rehm, D. Kovar, W. Kutschera,G. Stephans, and J. Yntema)
Reactions induced by medium-weight and very heavy projectiles are
usually thought to be dominated by deep inelastic reactions. Quasielastic
reactions are expected to contribute only a small fraction to the total
reaction cross section. We have investigated mass and charge transfer
reactions induced by 4 8Ti and 58Ni projectiles on 2 0 8Pb at energies about
25% above the Coulomb barrier. The particles in the outgoing channel were
momentum analyzed in the split-pole magnetic spectrograph and detected in
the focal plane by a position-sensitive AE-E ionization chamber. The
particle identification allowed the separation of individual elements and
isotopes around 4 8Ti and 58Ni. Figure 11-13 shows a mass spectrum for Z =
28 particles with a mass resolution Am/m < 6 x 10-3. The energy resolution
was limited by the 2 08Pb target thickness (100 pg/cm2) to about 800 keV.
Both 5 8Ni and 4 8Ti induced reactions show a deep inelastic reaction
component, which is well pronounded especially at forward angles.
Quasielastic reactions, however, are not negligible. Figure 11-14 shows
angular distributions for elastic and inelastic scattering and for the
(5 8Ni,5 9Ni) and (58Ni,6 0Ni) reactions, integrated over all excitation
energies. The total cross section for 1- and 2-neutron pickup is 260 mb
and 62 mb, respectively smounting to about 25% of the total reaction cross
section, as estimated from the quarter point angle. Differences in the
mass and charge flow observed for 4 8 Ti and 5 8 Ni induced reactions can be
explained by the underlying driving potentials.
95
I I
208'' I I I I I I
5 8
eN
650CHANNEL
i+ CvPb
b=375 MeV
b= 6 5 *
28
M=59
M=60
M=s
700NUMBER
Fig. 11-13. Mass spectrum for Z = 28.observed for 375-MeV 58Ni + 208Pb
at 6lab = 65*.
2001-
57
Eu mU.
150-
1001-
-JLuzzI
I-z00a
50
0r. fa - - m
I600
- -
M=6
I
I
F .
96
'01
b:
b
0.1
100
10
58Ni ,59Ni)
5864(58Ni, 0Ni)
1000 1200
Fig. II- . Ag ular distributions forand ( Ni, Ni) reactions on 208Pb
elastic
at Elab
+ inelastic (58Ni, 59Ni)= 375 MeV.
58Ni +208Pb
Elb =375MeV
ELASTIC +INELASTIC
E
b-o
00
o 200 40 80'600
ec.m.
--- ---T---
_ _ i _ _ i _
ldk A AdIL
i i i i I
tI
97/9
i. Observation of Characteristic Ga a RaygsfromlQuasi-Elastic andDeep-Inelastic Fragments in the Ni + Ni Reaction (W. Kuhn,P. Chowdhury, R. V. F. Janssens, and T. L. Khoo)
This experiment investigates the transition between quasi-elastic
reactions, which are strongly dependent on nuclear structure, and deep-
inelastic reactions, which are dominated by statistical features.
Encouraged by a preliminary expe:-iment described last year, a more
extensive experiment was performed where the gamma sum energy, and the
characteristic gamma rays from one and both of the fragments for
345-MeV 5 8Ni + 5 8 Ni were recorded. The analysis is currently underway.
Experiments at other incident energies and involving different target-
projectile combinations are planned.
99
D. ACCELERATOR MASS SPECTROMETRY (AMS)
Over the past few years the technique of AMS has developed into apowerful tool to measure extremely low conce tra ions 10-1 3O 10-15) of a
variet 4 of long-lived radi isotopes (1 Be, C, Al, Si, Cl,Ca Ti, 59Ni, 6 0Fe, 12 I). At present about 20 laboratories throughout
the world (mainly centered around tandem accelerators) are using thistechnique. Most of the laboratories have embarked on rather extensivemeasurements in applied fields (e.g. Geophysics, Hydrology, Archeology,Meteoritics). At Argonne a line more closely rel 9td to6nuclear physics ispursued. At present, measurements on half-lives 44 4 Ti, F 1 , exotic ions(doubly-charged negative), and on the detection of natural Ca areunderway. Both the tandem alone and the tandem-linac system in connectionwith Enge split-pole spectrographs are used. The higher energies from thelinac allow one to extend the measurements to heavier isotopes for betteridentification. In addition, for some cases the very clean separationtechnique of fully-stripped ions.
a. Measurement of the Half-Life of 4 4 Ti via Accelerator MassSpectrometry (D. Frekers, W. Henning, W. Kutschera,K. E. Rehm, R. K. Smither, J. L. Yntema, and B. Stievano*)
The half-life of 4 4 Ti has been measured from the specific
activity using the technique of accelerator mass spectrometry. The
interest in a remeasurement of the half-life arose from the fact that a
previously-performed irradiation of a 45Sc sample with 45-MeV protons had
yielded a substantial amount of 4 4 Ti, which could possibly be used for the
preparation of a target for future experiments. For the present
application of accelerator mass spectrometry, several TiO2 samples, spiked
with 44Ti of about 1.2-pCi total activity, have been prepared and used as
sputter targets for injection of a TiO beam. 44Ti was accelerated to 80
MeV in the FN tandem and identified in the Enge split-pole spectrograph at
6 = 00. The strong and ever present background contributions from
different ion beams with the same magnetic rigidity were effectively
eliminated using a second stripper foil in the spectrograph scattering
chamber and, by means of two movable shields, blocking all but the 15+
charge state from entering the focal-plane detector. A typical AE-E
spectrum obtained during the measurement is shown in Fig. 11-15. The
concentration of 44 Ti in the source material (4 4 Ti/Ti = 2 x 10-7) was
measured with rerpect to the yield of the 4 6Ti isotope. Mass-fractionating
^ifects were taken into account by measuring the relative beam currents of
*Istituto Nazionale di Fisica Nucleare, Legnaro, Italy.
100
ACTIVE SAMPLE
a
Ti
9Ti
=2.0 xO 4 4 .44
47 467
BLANK SAMPLE
44T< I I10
47 4 6 Ti48T 4 4TI
49Ti
44C
("'I'll 111VW
Fig. 11-15. An isometric view of the 2-dimensional AE-E spectrum for theZ % 22 region measured with the focal-plane detector of the magneticspectrograph. The lower part shows the result from a blank sample whereasthe upper part was obtained using a 4 4Ti-spiked sample. The variousbackground components are indicated.
o
4
102
the stable Ti isotopes (46-50Ti) for equal velocities at the terminal
stripper. An overall sensitivity for the 4 4 Ti concentration of 1 x 10-10
was achieved proving accelerator mass spectrometry to be a powerful tool
for radioisotope detection even for heavier elements. Our value for the
half-life of 4 4Ti, 54.2 2.1 y, turns out to be slightly higher than the
previously accepted value of 47.3 0.9 y (see Fig. 11-16).
b. Search for Doubly-Charged Negative Ions via Accelerator MassSpectrometry (W. Kutschera, D. Frekers, R. Pardo, K. E. Rehm,R. K. Smither, and J. L. Yntema)
Doubly-charged negative ions would be highly desirable for tandem
accelerators since the total energy gain of the ion beam could be
substantially increased. The production probability for these exotic ions,
however, is known to be extremely low. We have performed an ultrasensitive
measurement of the production rate of doubly-charged negative ions in a
sputter source using the techniques of accelerator mass spectrometry. If
ions fully stripped at the terminal are selected after acceleration in the
tandem, an unambiguous energy signature can be derived. Setting the beam
transport system to the corresponding rigidities, doubly-charged negative
ions can be identified in the Enge split-pole magnetic spectrograph under
very clean conditions. In our experiment we have focussed on the
investigation of 11B, 12C, and 160. These elements are known to produce
singly-charged negative ions with high probability. Several high-
sensitivity measurements were carried out and no doubly-charged negative
ions were identified at a level of 10-14 to 10-15 (with respect to singly-
charged negative ions). A search for singly-charged negative ions of He
and Ne was also performed. After stripping in the tandem foil, copious
amounts of 4He2+ ions (>103 per sec) were observed, but no signal
from 2 0Ne9 + ions in 30 min. He is known to have a half-life of 15 Iasec
%hich is in the same order of magnitude as the flight time from the ion
source to the terminal. It may therefore be concluded that if
Ne~, 11 B-- 1 2C~ and 160-- do exist, their half-life must be much shorter
than 1 sec or the production probability must be greatly suppressed.
101
I
+-- 54.2 2 .1y
+--- 47.3 0.9 y
456RUN
7 8 9 10
Fig. 11-16. The results of ten different half-life measurements, giving
a mean value of 54.2 2.1 y. The previously accepted value isindicated by the hatched area around 47.3 y.
62
6 0 -
58-
56T
NN~
54
52
50-
AQ
ALLh-T'
2 3
-- x r r y r r y r r y r
ZI&&
to
I
p
i
103
c. Accelerator Mass Spectrometry of lCa (W. Kutschera, D. Frekers,K. E. Rehm. R. K. Smither, J. L. Yntema, Ma Xiuzeng,*and M. Pault)
The goal of this experiment is to detect the long-lived
radioisotope 41Ca(T1 /2 = 1 X 105 yr) at natural concentrations estimated)
to be as low as 41Ca/Ca = 10-15. Since 41Ca is produced in the earth's
crust through thermal neutron capture from cosmic-ray secondary neutrons, a
successful method for 4 1Ca detection would offer numerous geo- and archeo-
chronological applications. In order to reach this goal several problems
have to be solved: 1) the isobaric interference of 41K must be removed, 2)
the background from stable Ca isotopes must be efficiently suppressed, and
3) the yield of negative Ca ions must be greatly increased. The last
problem appears to be the most difficult to solve.
So far the experiments were performed using the tandem
accelerator in conjunction with the Enge split-pole spectrograph as a
highly sensitive mass spectrometer. A schematic layout of the system is
shown in Fig. 11-17. 4 1 Ca/Ca ratios were measured from samples in the ion
source by identifying and counting 91-MeV 4 1 Ca ions in the split-pole
spectrograph and relating this number to a 4 0Ca current measurement in the
split-pole scattering chamber. With a careful consideration of relevant
normalizing parameters absolute ratios with a precision around 10% can be
measured.
The most convenient end product of any preparatory chemistry is
CaO. Therefore we used this material in the ion source. Since Ca does not
like to form negative elemental ions (even from metal Ca) one has to use
molecular ions. In a first run we tried CaO~ ions with little success.
Low yield and interferences from close-lying molecules made a clean
identification of 4 1 Ca impossible. Somewhat better was CaH. However, K
also forms KHi and hence the 4 1 Ca - 4 1K interference is not removed. In
the second run we used CaH3 ~ ions. The output was enhanced by spraying NH 3
onto the CaO samples. Apparently, KH 3 ions do not form in any detectable
quantity which solves the isobaric interference problem completely. This
*Institute of Atomic Energy, Peking, Peoples Republic of China.
tHebrew University, Jerusalem.
1G. M. Raisbeck and F. Yiou, Nature 277, 42 (1979).
104
SPUTTER BEAMEGATIVECTONSOURCE
ISO kV ELECTROSTATICPREACCELERATION QAR
ELECTROSTATICEIN LLENS
FAR ~4
INJECTIMAGNET ELECTROSTATIC
ER X-Y STEERERS
FN TANDEM
9MV
FIELJSTRIPPER
MAGNETIC 90
- QUAD POLE BJCT ANALYZING
FARADAY MA TIC_ CUP X-Y STEERERS
IMAGE SLIT
FARADY
SWITCHIMAC1-T
MAGNETIC
MAGNETICX-Y STE ER
SPLIT - POLEMAGNE TIC
x SPECTROGRAPH .010
Fig. 11-17. Schematic layout of the experimental system used inradioisotope detection with the FN tandem.
105
I I43Ca
ACTIVE SAMPLE
- 41 -Ca =3X0-8 42Ca Ca
10 min.
- Ca
40Ca
CCa-
BLANK SAMPLE
41- C-10-
--- _ 3xIO
- 55 min.-
80ETOTAL
9085(MeV)
Fig. 11-18. Total energy spectra of various Ca isotopesfocal plane detector of the split-pole spectrograph.energy of the ions is approximately 13 MeV lower thandue to the energy loss in the detector entrance foil.
measured in theThe measuredthe incident energy
410
I02
1210
I0
zzQ0
0 2
102
10
I75
i
106
confirms previous findings of Raisbeck et al.2. Figure 11-18 shows total
energy spectra measured for an enriched 4 1Ca material and a blank. Strong
background peaks of 4 3Ca and 42Ca appear because 4 1 CaH3 ~ is injected into
the tandem accepting 4 2 CaH2 and 4 3 CaH ions as well. By multiple charge
changes in the accelerator tubes these ions produce a "white" spectrum of
magnetic rigidities after the tandem from which small bins are cut out by
the purely magnetic transport system set up to accept 4 1 Ca 1G+ ions. An
addition of a Wien filter or an electrostatic separator should greatly
suppress this degeneracy.
40Ca10+ currents of 0.4 nA were measured for normalization. As
can be judged from the results of Fig. 11-18 we have yet to go a long way
to reach the goal of 4 1 Ca/Ca ratios around 10-15. Several approaches will
be tried: 1) Ca metal instead of CaO should yield a factor 100 more output
of CaH3- ions. Although factors of 700 have been measured in our
laboratory in the past, reproducible conditions have not been
established. 2) In order to reach highest sensitivity a background-free
condition must be established. We will try two different approaches. One
is to use a Wien filter for an isotopic cleanup in the present system. The
other is to use the tandem-linac system. Due to the stringent phase-
matching requirements, the linac acts as an excellent mass filter. In
addition, the increased energy after the linac would allow a much cleaner
identification as compared to tandem energies. Assuming an optimistic
increase of a factor 1000 for the Ca current and a background-free
condition, we would be able to measure a 4 1 Ca/Ca ratio of 1 x 10-15 with
one 4 1Ca count per hour. Such a condition has been achieved in several
laboratories for lighter, long-lived radioisotopes (e.g. 3 6C1) which,
however, easily form negative ions.
2G. M. Raisbeck, F. Yiou, A. Peghaire, J. Guillot, and J. Uzureau, Proc.
Symp. on Accel. Mass Spectrometry, Argonne 1981, Argonne Natl. Laboratory
Report ANL/PHY-81-1, p. 426.
107
d. Measurement of the Half-Life of 60Fe Using the Tandem-LinacSystem as an Accelerator Mass Spectrometer (W. Kutschera,P. J. Billquist, D. Frekers, W. Henning, X. Z. Ma,* L. F. Mausner,tM. Paul,* R. Pardo, K.E. Rehm, R. K. Smither,and J. L. Yntema)
The half-life of 6 0 Fe has been measured only once in the past'
yielding a value of T1/2 = 3 x 105 y, uncertain by a factor 3. The
recent finding2 of extinct 26AI activity (T1/2 = 7.2 x 105 y) through the
Allende meteorite makes 60Fe potentially interesting as a possible
signature of iron peak nucleosynthesis. An improved half-life value
for 60Fe could lead to its use as an interesting geo- and
cosmochronological tracer in the million-year range. In particular, a
measurement of 60Fe in meteorites3 with the highly-sensitive method of
Accelerator Mass Spectrometry (AMS) seems feasible.
We are presently engaged in an experiment to improve the accuracy
in the half-life value of 60Fe by measuring both the amount of 60Fe nuclei
and the decay rate of a spallation-produced sample using the relation
dN/dt = -AN. The sample material was produced by irradition of 4.5 g/cm2
Cu with 18.7 mAh of 193-MeV protons in the Brookhaven Linac Isotope
Producer (BLIP). Onc year after irradiation the iron fraction was
chemically extracted. This material contained approximately 1015 6 0Fe
nuclei besides mCi quantities of 5 5Fe (T1/2 = 2.7 y) and pCi amounts
of 5 9 Fe(T1 / 2 = 43.1 d). After an additional period of 5 months, the 6 0Fe
content was determined by adding a known amount of stable iron (>100 times
the original amount) and measuring the 60Fe/Fe ratio with AMS. For this
measurement several 130-mg Fe pellets were put into an improved inverted
*Institute of Atomic Energy, Peking, Peoples Republic of China.
tBrookhaven National Laboratory, Long Island, New York.
*The Hebrew University of Jerusalem, Jerusalem, Israel.
1J.-C. Roy and T. P. Kohman, Can. J. Phys. 35, 649 (1957).2T. Lee, D. A. Papanastassiou and G. J. Wasserburg, Geophys. Res. Lett.
3 109 (1976); Astrophys. J. 211, L107 (1977).
'P.S. Goel and M. Honda, J. Geophys. Res. 70, 747 (1965).
108
60Ni
xl
6Fe
ACTIVE Fe
300 6Fe/min60 Fe /Fe=1.2x 07
BLANK Fe
1.2 60Fe/min
6 0Fe/Fe = -9. x0
60.
F
60Fe /mi n
Cu
0. I
x0060F
aF ET Fe
Fig. 11-19. Isometric plot of energy loss, AE, vs. total energy signals,ET, measured in the focal-plane detector of the split-polespectrograph. All three dimensions are linear with the vertical scalevarying as indicated.
xIO
w
/a
1
wl
109//C
sputter source. 4 The tandem-linac system accelerated the mass-60 ions to
360 MeV and these were detected using and Enge split-pole magnetic
spectrograph. A strong 60Ni background cmponent following 6 0 Fe through the
entire acceleration process was separated by the difference in energy loss
in a 2.8 mg/cm2 thick Al foil stack. The subsequent position splitting in
the focal plane of the spectrograph allowed a physical shielding of the
main Ni component fromthe focal-plane detector. The resulting energy
spectrum measured with an ionization-type detector io shown in
Fig. 11-19. The 6 0 Fe/Fe ratios were obtained by normalizing to the 56Fe
current measured at the entrance of the linac. From 18 individual runs on
two active pellets, a 60Fe/Fe ratio of 1.16 x 10-7 with an uncertainty of
20% was determined. The relatively large uncertainty is due to systematic
errors in measuring an absolute ratio with such a highly complex system.
At present we are measuring the (slow) grow-in of the 6 0Co gamma-ray
activity (T 1 / 2 = 5.27 y, EY = 1.332 MeV). From preliminary values of this
measurement and the 6 0 Fe/Fe ratio we find that T1/2 Z 4 X 105y.
The 6 0 Fe/Fe ratio measurement has shown that AMS experiments can
be performed with the tandem'-linac system in the mass-60 range. An
extension to heavier radioisotopes seems possible, in particular when the
completed ATLAS system will provide heavy-ion beams pproaching 1 GeV.
Although combined accelerator systems beconw highly complex devices for
quantitative mass spectrometry, the current trend of steadily increasing
computer-assisted accelerator control may well make this type of
measurement more feasible in the future.
4J. L. Yntema and P. J. Billquist, Nucl. Instrum. Methods 199, 637
(1982)
111
E. SELECTED NUCLEAR SPECTROSCOPY AT THE TANDEM-LINAC
In addition to the programs described above, there are otheractivities at the tandem-linac. The main one involves on-line laserspectroscopy which has been initiated recently. The optical hyperfinestructure of radioactive atoms will be studied, in order to extractinformation on spins, moments, and the variation of charge radii for groundstates and isomers. The laser system has been installed and tests of thecryogenic helium jet which transports the atoms into the interaction regionhave been completed. Work is now proceeding on coupling the laser systemto the cryogenic helium jet. There has also been a search for a transientelectric field gradient acting on ions slowing down ig a solid.Measurements have also been performed on the? Be(p,Y) B r action, which isof astrophysical interest, of resonances in Be(a,Y) and Li(a'Y) and ofthe Be decay branching ratio.
a. Laser Spectroscopy of Radioactive Atoms (C. N. Davids,D. A. Lewis,* R. Evans,* M. A. Finn,t G. Greenlees,tand S. L. Kaufmant)
The linac target station for the cryogenic helium jet has been
completed. Tests using the linac beam have been conducted, indicating
copious production of Ba radionuclides using the 12 2 Sn(12C,xn)1 3 4-xBa
reactions. The skimmer efficiency for Ba is 2.5%, slightly higher than
that obtained for lighter As, Ge, and Ga isotopes. This is expected since
the opening cone angle at the capillary varies as M-1/2, where M is the
mass of the species. A large blower pump has been installed, and is
expected to produce a better vacuum in the helium exhaust chamber. This in
turn should lead td'better cooling of the atomic beam upon emergence from
the capillary.
The laser beam transport system between the laser laboratory and
the cryogenic helium jet has been installed. Tests to reduce the laser
light scattering background will begin soon.
Work with the stable atomic beam chamber has shown that the laser
line width is 7 MHz. This is quite adequate for the isotope shift
measurements. The light collection efficiency of the elliptical cylinder
light collector has been measured using a line filament light bulb. It
agrees with calculations, and should lead to a high overall efficiency for
detecting bursts of photons emitted by the excited atoms.
*Iowa State University, Ames, Iowa.
tUniversity of Minnesota, Minneapolis, Minnesota.
112
A data-acquisition system consisting of an LSI-1l/02
minicomputer, floppy disk drive, terminal, and CAMAC hardware has been
assembled. This system enables spectra of burst multiplicity to be
recorded. In addition, the computer controls the scanning of the dye-laser
frequency in precise steps.
b. Search for Transient Electric Field Gradient Acting onFast-Moving Ions in Solids (H. Ernst, W. Henning,T. J. Humanic, T. L. Khoo, S. C. Pieper, and J. P. Schiffer)
As a fast ion slows down in a solid the transient electric field
acting on it should give rise to a field gradient at the nucleus. Such a
field should interact with the quadrupole moment of the moving nucleus and
cause a perturbation in the angular correlation of the emitted Y rays. If
the gradient is sufficiently large it could be utilized as a powerful test
for measuring the quadrupole moments of states with lifetimes as short as a
few picoseconds. In our experiment we searched for a perturbation in the
angular correlation of Y rays deexciting the 2+ states of 56Fe and 24Mg,
which were both Coulomb-excited in the bombardment of 24Mg with 125-
MeV 5 6 Fe beams from the linac. No effect was detected within experimental
limits and an upper limit of 1021 V cm-2 was set for the electric field
gradient. A paper has been published in Physical Review on the results.
c. The 7 Be(p,Y) 8 B Reaction (B. Filippone,* A. J. Elwyn, C. N. Davids,D. Koetke,t and W. Ray, Jr.)
The 7 Be(p,Y)8B reaction has been measured from Ecm = 117--1230
keV by detecting the delayed a particles from the 8B 0 decay. The
occurrence of this reaction in the sun produces high-energy neutrinos which
account for nearly 80% of the neutrino capture rate in the 37C1 solar
neutrino experiment.
A 7Be radioactive target (t1/2 = 53.3 days) of 80 mCi was
produced by a high-voltage electroplating technique in an organic
solution. The 7Be was produced via the 7 Li(p,n) 7 Be reaction and then
chemically separated from the 7 Li and purified.
*Thesis Student, University of Chicago, Chicago, Illinois.
tValparaiso University, Valparaiso, Indiana.
113
10 :-
-i 2
b
10 ---
I0
0 400 800 1200Ec.m.(keV)
Fig. 11-20. Total cross section for the reaction Be(p,y)8B as a function
of the center-of-mass energy. The solid curve is the cross sectioncalculated from the theoretical s-factors of Ref. 1, normalized to the
data.
1T.A. Tombrello, Nucl. Phys. 71, 459 (1965).
114
The 7Li(d,p)8Li and 7Li(p,Y)8Be reactions were used to analyze
the target characteristics (from the 7 Li built up from7Be decay) along
with a Pb- collimated NaI detector which scanned the T-ray activity of the
target.
Figure 11-20 shows the measured total cross section as a function
of center-of-mass energy. The extracted astrophysical S-factor from the
present experiment is S17(0) = 0.0216 0.0025 keV-b. This value lowers
the predicted solar neutrino capture rate in the 37C1 experiment by ^25%.
d. Resonances in 7Be(aY) and 7Li(a,y) (A. J. Elwyn, B. Filippone,*G. Hardie,t R. E. Segel,* and M. Wiescher )
A target containing about 80 m Ci (2 x 101 6 atoms) of 7 Be was
bombarded by alpha particles from the Argonne Dynamitron with the capture
gamma rays detected by ? large NaI(T2) crystal and by a Ge(Li)
spectrometer. The detector efficiences were obtained by measuring the
spectrum from the 992-keV 2 2 A1(p,y) resonance. From the thick-target
yields 7Be(a,y) resonance strengths wr = (0.34 f 0.07) eV and (4.45 1.2)
eV were found for the 880-keV and the 1380-keV resonances, respectively.
It is apparently the first time that these yields have been measured. For
the 7Li(a,y) reaction preliminary analysis yields wL = 0.012 eV, 0.54 eV,
and 1.95 eV for the 401-keV, 820-keV, and 958-keV resonances,
respectively. The value for the 820-keV resonance is in good agreement
with that given in the compilation but the previously accepted values for
the other two resonances are considerably higher. Reasons for accepting
the present values will be given. Branching ratio data were obtained for
all the resonances and the individual radiative widths show some agreement,
and some disagreement, with theoretical predictions.
*Thesis student, University of Chicago, Chicago, Illinois.
tWestern Michigan University, Kalamazoo, Michigan.
*Northwestern University, Evanston, Illinois.
Ohio State University, Columbus, Ohio.
115
e. The 7 Be Decay Branching Radio (C. N. Davids, A. J. Elwyn,B. W. Filippone, S. B. Kaufman,* K. E. Rehm, and J. P. Schiffer)
The branching ratio for the electron capture decay of 7Be to the
first excited state in 7Li is an important number in astrophysics. The
currently accepted value for the branch...ng ratio is 10.37 * 0.12%, but a
recent preprint by Rolfs et al. reports a value of 15.4 * 0.8%. We have
measured the branching ratio by implanting 89.04 x 106 7Be nuclei in a Si
surface barrier detector and subsequently counting the 478-keV decay Y rays
in a well-shielded Ge(Li) detector. The Be nuclei were produced via
the 1H(7Li, Be)n reaction at 15.5-MeV bombarding energy, and were allowed
to recoil into an Enge split-pole spectrograph placed at 1.60 to the
incident beam. A clean separation of 7 Be from contaminants allowed
placement of the Si detector in the magnet focal plane, and an analysis of
the energy spectrum in the detector yielded the total number of 7 Be
nuclei. Figure 11-21 shows the energy spectrum for one of the runs lasting
about 40 minutes. The resulting branching ratio is 10.61 f 0.23%, which
agrees with the currently accepted value.
*Chemistry Division, ANL.
116
' I I
123+
\C
7.2+Li- 9
4H
IB3+ 1
200I 0
' I
SCATTERED7 .3+
PULSER
/i14N4+ 17 5+
1I4+B4 B 14N5+
e3+ 9Be4+2+e
I706+
12C5+
04 1605+ 1505+
i I400 600 800 1000
CHANNEL NUMBER
Fig. 11-21. Energy spectrum in Si detector mounted in the focal plane ofthe Enge split-pole spectrograph. The double peak marked "Li isdue to slit-edge scattered beam particles. Other identified peaks aredue to 7Li-induced reactions on Li and 12C.
' I
Be
' I
4N6+
10
10
-JzzI0
C!)Fz00
l03
210
10
-
| 1 ls -L
117
F. EQUIPMENT DEVELOPMENT AT THE TANDEM-L INAC FACILITY
The experimental areas of the linac are now reachingcompletion. The Enge spectrograph is operational on a routine basis, andsignificant improvements have been made to its focal-plane detector. The65" scattering- chamber has been continually upgraded primarily to permitmore refined operation with longer flight paths. Detectors have beendeveloped for efficient detection of heavy evaporation residues and topermit high resolution time-of-flight measurements. A new beam line hasbeen installed with two target stations. One has a thin-walled Al chamberfor neutron time-of-flight measurements and the other incorporates anupgraded Y-ray facility. A plunger which fits inside the sum spectrometerhas been extensively tested and used successfully in several experiments.A general-purpose beam line has been installed and used in several atomicphysics experiments, while a beam line for a superconducting- spectrometeris almost complete. Effort has also been devoted to planning for the ATLASfacility. This activity is described elsewhere in this document.
a. Ray-Tracing Corrections for the Focal-Plane Counterat the Spectrograph (K. E. Rehm)
Reactions between two medium-weight nuclei usually show a large
kinematical shift. For experiments with the split-pole spectrograph this
implies that the detector has to be moved very close towards the exit of
the magnet, which is not possible for many cases due to mechanical
reasons. It is, however, possible to reconstruct by ray-tracing techniques
the actual focal plane from two position measurements taken outside the
focal plane. From our measurements with two position wires, separated by
50 mm, we have obtained energy resolutions of ~1 x 10-3 after the ray-
tracing correction. An example of the reconstruction of the actual focal
plane is shown in Fig-. 11-22 for the case of elastic scattering- of 50-
MeV 160 on 27Al at blab - 200. The same technique can also be used to
correct the angle dependence of the AE signal. This strongly improves the
Z resolution for heavy-ion reactions at large solid angles. Ray-tracing
corrections are also of importance in future experiments with the split-
pole spectrograph at the ATLAS accelerator. Presently we are working on
the implementation of the ray-tracing correction into the on-line data-
acquisition program.
FOCAL PLANEWIRE IWIRE 2
0 400 800 1200 1600 2000
480 Bp SPECMEASUREWIRE I
TRUMD A
Bp SECTRM CLCUAE
320E
1601
200-
160-
1201-
801-
40
Bp SPECTRUM CALCULATED
FOR ACTUAL FOCAL PLANE
420 460 500 540 580CHANNEL NUMBER
Fig. I1-22. Reconstruction of the actual focal plameasurements.
620
ne using two position
118
1500
1000
500k
-JUzzI<-)
U)
I-zD0U-
500 540 580 620 660 700
20001
ir-I 1 1 md&
VIA l u
119
b . Test of the Large Focal-Plane Counter for the Linac MagneticSpectrograph (K. E. Rehm, W. Kutschera, and D. G. Kovar)
Experiments with high-energetic (~10-MeV/nucleon) heavy ions in
the magnetic spectrograph require large focal-plane detectors with good
resolutions to identify the detected particles. We have thoroughly tested
a 25-cm deep position-sensitive ionization chamber with 160, 37Cl and 5 8Ni
ions. This detector is now used routinely for experiments at the linac
spectrograph. Resolutions obtained with 150-MeV 160 ions were: QE : 2.9%,
E : 0.75%, position : 1 mm. The improvements in the QE and E resolution
are mainly due to the use of CF4 as counter gas, which has the additional
advantage of being nonflammable. This allows us to study nuclear reactions
between medium-weight nuclei on heavy targets with better resolution than
hitherto possible. We are planning to add a parallel-plate avalanche
counter to the present system for time-of-flight information to improve the
mass resolution for experiments with projectiles in the A = 100 region.
c. A AE-E Detector for Fusion Measurements (W. S. Freeman,H. Ernst, D. F. Geesaman, W. Henning, W. KuYhn, J. P. Schiffer,and B. Zeidman)
An improved AE-E detector has been constructed for identifying
evaporation residues from heavy-ion fusion reactions. The detector
consists of four silicon surface-barrier detectors (450 mm2 x 300 u thick)
placed inside a AE gas-filled ionization chamber. The back plate on which
the silicon detectors are mounted may be easily removed and replaced with
another plate whose design and function is at the user's discretion. The
maximum available gas volume of the ionization chamber is 19 mm height x
152 mm length x 60 mm deep, and provision is made for installing a grid to
support thin windows (100 pg/cm2). The detector has been used
successfully in conjunction with an electrostatic deflector to measure
evaporation-residue angular distributions for several moderately heavy
systems (AN~ 180). In the course of these measurements, the limitations
of the AE-E method for detecting and identifying very heavy, low-energy
evaporation residues has become apparent. In the future we plan to
incorporate time-of-flight measurements into the system as an additional
means of identification.
120
d. Modifications to the 65" Scattering Chamber For LongFlight-Path Measurements (D. G. Kovar, R. Nielsen, and G. Rosner)
Modifications to the 65" scattering chamber have been made to
allow for x1.5 meter flight paths for time-of-flight measurements. A new
target position was installed at the entrance of the chamber with a
collapsible movable arm attached to the new target position and an existing
ring in the chamber. As the ring is rotated in the angular range 00 to
1000 the new arm rotates from 00 to 550 and the flight path varies from
41.5 to 1 meter. A target holder with eleven target positions has been
installed for measurements. This configuration has been used in
measurements using two micro-channel detector systems plus a Si detector
and masses of "55 amu have been resolved in studies of evaporation
residues. Further modifications to allow for coincidence measurements
using the new target position are planned.
e. The Y-ray Facility (P. Chowdhury, W. Evans, H. Emling,*R. V. F. Janssens, T. L. Khoo, and J. Worthington)
The Y-ray facility has been moved to another location in the new
linac target area annex. As a consequence there is now more space around
the target for large NaI detectors or for neutron time-of-flight
measurements, thereby alleviating the congestion in the previous
location. Improvements to the vacuum system and beam-diagnostics have also
been made.
Extensive tests of a plunger for recoil-distance measurements
have been conducted. The plunger incorporates several unique features,
among them the support of the catcher foil on 3 independent push rods and
the use of a microcomputer to control the rods. Tests have demonstrated
that the position of the catcher foil as given by the microcomputer is
accurate to within 1 in. In addition, a new algorithm has been developed
for quick remote adjustments to achieve parallelism between target and
catcher foils. Measurements of state and feeding times as a function of Y-
sum energy have been performed in 1 5 2, 1 5 4Dy, as described in sections A.c.
and A.f. Future experiments will include similar measurements
*GSI, Darmstadt, W. Germany.
121
in 1 4 7Gd, where we have identified yrast states to the highest spins known,
in 1 8 6Hg, and in some light Re isotopes. In the latter cases the core is
soft toward deformation: lifetimes will provide important information on
the deformation parameters and on their changes with spin.
Design studies are currently being undertaken for a facility
consisting of (a) a sum-energy/multiplicity analyzer consisting of 60
bismuth germanate (BGO) detectors and (b) an array of 7 anti-Compton
spectrometers, where BGO is used for detecting Y-rays which are Compton-
scattered out of the Ge detector. The anti-Compton array will be arranged
outside the sum-energy/multiplicity analyzer. Such a device will enable
the nucleus to be probed to higher spins than has hitherto been possible
with any existing detector systems. The sum energy/multiplicity filter
will also provide valuable data in the study of reaction mechanisms.
f. Superconducting Solenoid Lens Electron Spectrometer (P. J. Daly,*Z. Grabowski,* W. Evans, R. V. F. Janssens, T. L. Khoo,and J. Worthington)
Work has continued for the construction of the Purdue
superconducting electron spectrometer to be installed at the linac. The
coils were delivered by the middle of the year. Field mappings were
performed. They show that the original design goals are met and even
exceeded. No particular problems were encountered in realizing the high
magnetic fields.
Meanwhile, the beam-line design has been finalized at Argonne and
construction has started. First studies of the beam quality through the
line are expected in spring 1983. The installation of the spectrometer
should take place before the end of the year. A variety of experiments is
planned, some of which will take advantage of the possibility of measuring
e--e- coincidences.
*Purdue University, W. Lafayette, Indiana.
122
g. General-Purpose Beam Line
A general-purpose beam line has been constructed to which
equipment may be attached for limited time intervals. Outside users or
those with no facilities at the present permanent stations will be able to
take advantage of this facility. It has already been used in several
atomic physics experiments.
The target system for atomic physics experiments will include a
scattering clamber for ion-atom and ion-foil collisions. Such a chamber
(diameter 140 cm) would be attached to a high-resolution electron
spectrometer, and also be used for Coulomb-explosion experiments involving
charged-particle detection. A second target chamber further downbeam will
be available for photon spectroscopy measurements of ion-atom and ion-foil
collisions. Pumping systems will include two turbo-molecular pumps and an
ion pump.
h. Nuclear Target Making and Development (G. E. Thomas)
The Physics Division has a facility which is used principally to
produce very thin films for experiments at the Tandem-Linac and Dynamitron
accelerators as well as for experiments of other members of the Division.
In addition, it is available to any other division at the Laboratory
needing this service and occasionally to other laboratories and
universities.
This year we again produced targets varying in thickness from a
few monolayers to several mg/cm2. The different elements, isotopes, or
compounds evaporated or rolled included the following: Au, Al, BaF2 ,10,11,normalB, Bi, C, 4 Ca, CH2' 155,156Gd, 76Ge, K, 6,7,normalLiF,
LiH, Li, 24,26,normalMg, gF2, 92,94,95Mo, 58, 62Nc, 206,208,normalPb,96Ru,112 ,114 ,116 ,118 ,120 ,122 ,124Sn, 28,29,30,normals5 , 1 25Te, and92 ,94Zn.
Methods have been developed to better produce the more complex
targets made for experiments at the heavy-ion facility. One such type is a
"sandwich" produced by evaporating an absorber material (15 mg/cm-2 ) onto a
rolled separated isotope target (1 mg/cm- 2 ) or the target (1 mg/cm- 2 ) may
123
be evaporated onto the rolled absorber material (15 mg/cm- 2 ). Another type
is produced by evaporating the separated isotope (1 mg/cm 2 ) onto a very
tightly and smoothly stretched Au (1 mg/cm- 2 ) foil. "Sandwich" targets
produced by the above methods include 1 5 5 , 1 5 6 Gd + Pb, 1 5 6 Gd + Bi +
Pb, 92,94,95Mo+Pb,b58,62Ni + Pb, 122,124Sn + Au, 12 5Te + Pb, and 9 2 , 9 4 Zr
+ Pb.
New systems being developed for the facility include a
computerized target-storage system using turbo-pumps (work in collaboration
with J. N. Worthington and B. G. Nardi), a system for producing targets
using a new type of sputter source, and a clean evaporator system using a
cryo-pump. Plans for the future also include building a new type of multi-
target evaporator system using a rotating wheel. A continuing objective is
to improve target quality.
1251P6
III. THEORETICAL NUCLEAR PHYSICS
Introduction
The principal areas of research in the nuclear theory programare:
1. Nuclear forces and sub-nucleon degrees of freedom.2. Variational calculations of finIte many-body systems.3. Nuclear shell theory and nuclear structure.4. Intermediate energy physics with pions, electrons and nucleons.5. Heavy-ion interactions.
In 1983 encouraging results were found for the strong couplingapp oximation to the static chiral bag model of the nucleon. The treatmentof He, including 3-body forces, was extended to several excited stateswith good results. The nuclear structure calculations of the effects of A
admixture obtained a striking result, namely that in simple nucleisuppression of M1 matrix elements is much stronger for nondiagonal casesthan for diagonal cases like magnetic moments, in agreement withobservation. Consideration of possible experiments with a GeV electronaccelerator was stimulated by a series of lectures given by visitingArgonne Fellow, J. Dirk Walecka.
127
A. NUCLEAR FORCES AND SUBNUCLEON DEGREES OF FREEDOM
F. Coester, B. D. Day, T.-S. H. Lee, J. Parmentola,R. Wiringa, and collaborators from other institutions
Much of our work is motivated by three central questions. (1)What should be the active degrees of freedom? (2) What is the Hamiltonianthat governs the nuclear many-body dynamics? (3) What can electromagneticprobes reveal about short-distance nuclear structure?
For the conventional nuclear theory which assumes that nucleonsare the only active degrees of freedom it is not required that two-bodyforces alone are sufficient, but it is essential that the same Hamiltonianaccount for both light and heavy nuclei and that the importance of the n-body forces decrease rapidly with increasing n. We have previouslyestablished that two-body forces alone cannot account for the properties ofnuclear matter. During 1981-833we investigated the effects of severalthree-body interactions in H, He, He and nuclear matter. Inclusion ofthese three-body forces is a marked improvement, but open questions remain.
A promising extension of the conventional theory includes the Aisobar among the active degrees of freedom. This step may drasticallyreduce the need for explicit three-body forces. We have constructed arealistic two-body potential with NA interactions. We expect that adetailed comparison of the properties of different models will lead to abetter understanding of three-body forces and the role of isobars.
The role of quark degrees of freedom in nuclear theory dependscritically on the quark distribution within the nucleon. The assumption ofa "little" quark bag surrounded by a pion (or qq) cloud leaves room formuch of the conventional meson-nucleon dynamics. However, in such modelsthe pion cloud strongly contributes to the structure of the nucleon and anaccurate solution of the one-nucleon problem is a prerequisite for furtherapplications. We have been investigating properties of static chiral bagmodels in the strong coupling approximation.
Constituent quark models with QCD based potentials also predict asmall radius of the constituent quark distribution. Such models accountwell for the spectroscopy of single hadrons, but in their present form theydo not provide a satisfactory multi-hadron dynamics. Along these lines weare working on the development of models designed to include meson creationand hadron-hadron interactions in a satisfactory manner.
Much of the quantitative information that will determine thesuccess or failure of competing models will come from electromagneticprobes. Observed quantities are directly related to matrix elements of theelectric charge and current densities. Probes of short range featuresinevitably involve relativistic effects. A valid interpretation requiresmutually consistent representations of the current operators and the targetwave functions. Work is in progress on the construction of relativisticcurrent operators that are consistent with relativistic particle models.
128
a. Three-Body Forces in Light Nuclei and Nuclear Matter(R. B. Wiringa, J. Carlson* and V. R. Pandharipande*)
Realistic models of three-nucleon interaction (TNI) have been
examined in 3H, 3He, and 4He nuclei, and in nuclear matter. Two-nucleon
potentials that fit NN scattering data, such as Reid, Paris, and
Urbana-v14 , consistently underbind the light nuclei while overbinding-
nuclear matter at too high saturation density. The addition of TNI to the
many-body Hamiltonian can significantly lessen this problem. The Tucson
and isoba. intermediate-state models of the two-pion-exchange potential
(V2w3N) were studied along with an intermediate-range three-nucleon
repulsion (V 3 NR). The Urbana-v1 4 model was used for the two-body force,
and variational upper bounds were calculated for the full Hamiltonian.
Energy expectation values were evaluated by Monte Carlo sampling in the
light nuclei, and with Fermi-hypernetted-chain techniques in nuclear
matter. The nuclear matter calculations are the first to treat TNI without
an "effective" two-body potential approximation.
The realistic TNI bring- theory closer to experiment by giving
extra binding- to the light nuclei and reducing- the saturation density of
nuclear matter. For example, one model with V2n3N and V 3 NR changes the
two-nucleon Urbana-v1 4 results from -7.2 MeV to -8.1 MeV in 3H, and from
-25 MeV to -29 MeV in 4 He (experimental values are -8.48 MeV and -28.3 MeV,
respectively), while the saturation energy in matter is changed from -20
MeV at p = 0.38 fm- 3 to -14 MeV at p = 0.21 fm 3 (empirical value is -16
MeV at p = 0.16 fm-3 ). The Coulomb energy of 3He and the rms charge radii
of the light nuclei are also well described. However the charge form
factors are not close to experiment, probably due to meson-exchange
currents. A paper covering- this work will be published shortly in Nuclear
Phy ics.
We have extended our studies to the lowest-lying- excited states
of 4 He, which include a 0+ breathing mode at 20.1 MeV excitation and 0 and
2 p-wave resonances at 21.1 and 22.1 MeV. These states are unstable
against breakup into p + 3H or n +3 He. A modification of our variational
Monte Carlo method suitable for such unconfined states is used. For the
Hamiltonian mentioned above we find upper bounds for these three excited
*University of Illinois, Urbana, Illinois.
129
2+,0
I-,0
0 -, I
4
2
0
-2
- 2-,0
0-,0
- 040
- 0*90
2-,0
0-,0
d+ 2 H
o-,o
+3 He-- -p + 3H
0+,0
Fig. III-l. Excited states of 4He: the columns show the experimentalspectrum, a Coulomb-corrected spectrum with estimates for theCoulomb energy removed, and the corresponding calculatedspectrum.
2-,I
-4H
-6
- 8
-281
-30
o*,o
0o,0
J 11T Coulomb CalculationEXPT Corrected
"Expt "
130
states at 21.3, 23.6 and 26.8 MeV, with the correct ordering, about 5--20%
above the experimental values (see Fig.III-1). A separate paper covering
this work has been submitted to Nuclear Physics.
b. Present Status of the Nuclear Saturation Problem (B. D. Day)
A basic question in nuclear physics is how nuclear binding
energies and radii, e.e., saturation properties, follow from the
interactions among the constituents of the nucleus. Ultimately this should
be understood in terms of quarks and gluons. At present the most
fundamental treatment for which reliable calculations are possible takes
the nucleus to consist of nucleons interacting through potentials. The
two-body potential is required to fit nucleon-nucleon scattering data up to
350 MeV and to be consistent with our understanding of particle physics,
the most important requirement of the latter type being an OPEP tail.
Coupled-cluster calculations at Argonne and Bochum, and variational
calculations at Urbana and Argonne, have shown that two-body potentials are
inadequate: in most cases they give too high a saturation density for
nuclear matter and substantially underbind light nuclei. Therefore, recent
variational calculations by an Argonne-Urbana group have included three-
body potentials. Roughly 80% of the discrepancies can be removed by
including a three-body force that is repulsive at short range and
attractive at long range. The calculated saturation point in nuclear
matter is at a density about 10% too high, with about 1 MeV per particle
too little binding. If the binding energy of 3H is fitted, then 4He is
overbound by 1--2 MeV. The great improvement means that further work with
three-body forces is essential. A paper giving an overview of the present
situation has been accepted for publication in Comments on Nuclear and
Particle Physics.
c. Studies of Three-Body Forces and Isobar Degrees of Freedom inNuclear Systems (R. B. Wiringa)
The effect of three-body forces in light nuclei, nuclear and
neutron matter is being studied with both phenomenological three-nucleon
potentials and interaction models that explicitly include isobar degrees of
131
freedom. The interplay between two- and three-body forces has been studied
by repeating the calculations with phenomenological three-nucleon
interaction (TNI) described above with a different two-body force, Argonne-
v1 4 (see below). Argonne-v14 has a 6.1% deuteron D state which induces
stronger tensor correlations than the Urbana-v1 4 model's 5.2% D state.
Consistent with the lore of tensor forces in nuclear systems, Argonne-v1 4alone gives less binding, but when TNI is added it actually gives a little
more, due to the attractive combination of the two-pion exchange potential
V2n3N and strong tensor correlation. The results of calculations for light
nuclei are shown in Table III-1 and for nuclear matter in Fig. 11-2. A
paper on this work has been accepted for publication in Nuclear Physics.
Calculations of neutron matter are now in progress. Comparison
of nuclear and neutron matter energies at the empirical saturation density
of nuclear matter, p0, yields a symmetry energy for the Argonne-v1 4 + TNI
Hamiltonian of 30 MeV, of which ~-10% comes from the TNI. This is in
reasonable agreement with semiempirical mass formulae which typically give
30--38 MeV. The equation of state for neutron matter will be used as input
for neutron star calculations to see the effect of TNI on star structure.
It should be dramatic, since the TNI are repulsive here and begin to
dominate the energy around 2p0. This will give a stiffer equation of state
than for two-body forces alone, and a consequent larger maximum star
mass. It will also have implications for supernovae models.
There is now a dispute over the contribution of TNI in the
triton. Two Faddeev calculations in momentum space have now been done by
other groups using the Tucson model TNI, and both get about zero net
contribution. Since our variational calculations give '-1 MeV and should
be rigorous upper bounds, there is a serious discrepancy here. Assuming
there are no bugs in the variational codes, it would indicate that channels
not normally used in Faddeev triton calculations have a large effect on the
TNI contribution. One way to check this is to take the Faddeev wave
functions and calculate expectation values with Monte Carlo methods. The
Los Alamos Faddeev group has offered to provide the wave functions and we
hope to make this calculation in the near future.
An alternative to the phenomenological TNI is to construct two-
body potentials with both nucleon and isobar degrees of freedom. In a
132
Table III-1. Properties of light nuclei with Argonne v1 4 (Urbana
v1 4 ) two-nucleon potential and different three-nucleon potentials: model V
with isobar intermediate-state two-pion-exchange plus repulsive terms and
Tucson two-pion-exchange model. Terms in brackets < > give expectation
values for two- and three-nucleon potentials, while E-V and E-Tucson give
total energies.
3 He 3H 4 He
kinetic 48.8 (44.6) 51.1 (46.5) 109.3 (103.6)
<v14> -55.6 (-51.8) -57.9 (-53.5) -132 (-127.3)
Coulomb .69 .69) 0 (0) .77 (.78)
(Vijk>V - 1.37 (-.97) -1.47 (-1.06) -7.49 (-6.23)
<Vijk>Tucson - 1.28 (-1.02) -1.33 (-1.09) -7.69 (-6.48)
E-V - 7.5 .l(-7.4 .l) -8.2 .l(-8.1 .1) -29.6 .4(-29.l .4)
E-Tucson - 7.4 .l(-7.4 .l) -8.1 .1(-8.1 .1) -29.8 .5(-29.3 .5)
E-expt. - 7.72 -8.48 -28.3
<r2>1/2 -calc. 1.82 (1.86) 1.73 (1.76) 1.62 (1.63)
<r2>/ 2 -expt. 1.84 .05 1.70 .05 1.67 .03
133
*1' I ' I ' ' -- - I ' -
-10 S
EMPIRICAL
v14-20 - -
ARGONNE----- URBANA TUCSON
-.0 1.2 1.4 1.6 1.8 2.0-I
kF(fm
Fig. 111-2. Nuclear matter energy: curves labeled "v1 4 "', "V" and"Tucson" show results with Argonne v 1 4 and Urbana v14 two-nucleonpotentials alone, with model V, and with Tucson model three-nucleonpotentials, respectively.
134
many-body environment many of the processes contributing to the three-body
forces will then be automatically incorporated as soon as three-body
clusters are considered. Fermi-hypernetted-chain techniques for
variational calculations of nuclear matter with such potentials have been
developed previously. However the available published potentials of this
type have a variety of deficiences, so we have concentrated on building a
more reliable potential with NA interactions (see below). This potential,
Argonne-v2 8 , has now been completed and we plan to return to the nuclear
matter calculations in the near future. We hope that detailed comparisons
of nuclear systems with Argonne-v14 + phenomenological TNI versus Argonne-
v28 will lead to a better understanding of three-body forces and the role
of isobars.
d. Nucleon-Nucleon Potentials with Isobars (R. B. Wiringa, R. A.Smith,* and T. Ainswortht)
An NN potential model called Argonne-v 2 8 that includes NN-NA and
NN-AA transitions has been constructed. The intermediate-range attraction
observed in NN scattering can be attributed largely to two-pion-exchange
processes with possible isobars in the intermediate state. Part of these
processes behaves like a twice-iterated one-pion-exchange potential with
NA coupling. The description of many physical processes, where isobars
are believed to play an important role, will benefit greatly from reliable
NA transition models with good fits to the scattering data.
In present work, the isobar is treated as a stable particle. A
one-pion-exchange potential, containing 1NN, iNA, and iAA couplings is
supplemented by phenomenological intermediate and short-range terms. The
NN-NN part is taken in a v1 4 form, i.e., fourteen operator components, and
with the transitions added, a total of 28 operators appear in the full
potential. The coupled-channel Schr6dinger equation is solved for the
deuteron and all J45 partial waves in the NN channel for a variety of
energies up to 400 MeV. This includes up to twelve coupled channels in
the 3 F4 - 3 H4 component. The phenomenological part of the potential is
*Texas A & M University, College Station, Texas.
tState University of New York, Stony Brook, New York.
135
I.i
150- -c
I,0
100 .
0,
-50-
-100- -- '-
0 0.5 1.0 1.5 2.0
r (fm)
Fig. 111-3. Effect of coupling NN to NW and WW channels on the S0, T-1central (vc) and '2(vq)NN potentials: dashed line shows v1 4 modelwith no coupling, dotted line a model with coupling to NW channels,
and solid line the v 2 8 model with coupling to NW and WW channels.
adjusted to obtain good fits to np phase shifts. A direct comparison to
1760 np data points in the range 5--330 MeV shows an excellent fit with a
x2/point of 1.70. Deuteron properties are also well reproduced.
As an exercise in learning how to efficiently search in a large
parameter space for the best fit, the code was also used to construct a
conventional NN potential, Argonne-v1 4 . This potential was built with the
same structure as the Urbana-v1 4 model, for which reliable variational
many-body calculations have been developed. It has already been used in a
study of phenomenological three-body forces (see above). It also gives an
excellent fit to data, and has a similar structure to the v2 8 model to
facilitate comparison of results from many-body calculations. A comparison
of the v1 4 and v2 8 potentials in NN S-0, T-1 channels is shown in Fig. III-
136
3. Because of the effective attraction provided by coupling to NA and AA
intermediate states there is significantly less attraction required in the
NN channel for the v2 8 model.
In future work it would be useful to fit the scattering data at
higher energies, including inelasticities. In particular the possible
existence of resonances in the S and P wave NA system, which would show up
in the 1D2 and 3F3 NN channels, could place significant constraints on the
nature of the diagonal NA-NA interaction. To make such fits, relativistic
effects and the instability of the A will have to be taken into account.
We hope to tackle this problem in the next year.
e. Consistency of Electromagnetic Current Operators andRelativistic Wave Functions (F. Coester and M. J. King*)
Intense electron and photon beams provide much of the precision
data on the structure of nuclei and the properties of nuclear matter.
Probing short range structure requires large momentum transfer which
inevitably involves relativistic effects. The directly observed quantities
are the matrix elements of the electric charge and current densities.
Inference from the data about the structure of the nuclear target requires
a mutually consistent representation of the current operators and the wave
functions representing the states of the target. The representations of
the Lorentz transformations depend on the forces governing the target
structure. It follows that current operators satisfying the covariance
relations of free particles are not covariant in the presence of
interactions. By combining results from quantum field theory and
constraint dynamics we have found a systematic construction of the two-body
current operators required by Lorentz covariance. The construction does
not depend on an expansion in powers of the particle velocities. A
preliminary report on this work was presented at the Sixth Pan American
Workshop on Condensed Matter Theory at St. Louis, Sept. 20-Oct. 1, 1982. A
paper for publication is in preparation.
*SOHIO Technical Center, Cleveland, Ohio.
137
f. Relativistic Quantum Mechanics of Particles with DirectInteractions (F. Coester and W. N. Polyzou*)
Relativistic quantum mechanics requires a unitary representation
of translations and Lorentz transformations on the Hilbert space of
states. Causality requires that systems localized in relatively space like
regions be dynamically independent at least for macroscopic distances. We
have realized both requirements by an explicit recursive construction for a
fixed arbitrary number of interaction particles. The Hamiltonian is in
many ways similar to the nonrelativistic many-body Hamiltonian. Under
conditions of physical interest the strength of the required N-body
interaction decreases rapidly with increasing N. The construction can be
generalized to allow for particle creation. Relativistic effects in nuclei
are the prime area of application of this theory. A paper on this work has
been published in Phys. Rev. D.
In its present form it is essential for theories of this type
that all particles and bound clusters become free when they are widely
separated, i.e., the forces are short range. The treatment of confining
forces involves new problems. Constituent quark models have been
quantitatively successful only for single hadrons. The construction
constituent quark models of multihadron systems is an open challenge. Work
on these problems is in progress.
*Massachusetts Institute of Technology, Cambridge, Massachusetts.
g. Static Bag Source Meson Field Theory (John A. Parmentola)
An important factor in the role quarks will ultimately play in
nuclear physics is the size of the quark core of the nucleon. Is its
radius about equal to the charge radius of the proton or is it much
smaller? Chiral bags provide useful models for the study of the
consequences of various assumptions. The effective coupling to the meson
field is stronger for smaller bags. For "little bags" perturbative
treatment of the meson field or the truncation of the Fbck space to one or
two mesons do not yield legitimate approximations and some modes of the
meson field become collective degrees of freedom of the physical nucleon.
138
In general these collective degrees of freedom cannot be treated
classically. For exploratory purposes we have investigated in quantitative
detail a static source meson field theory in which only the nucleon isospin
degrees of freedom are coupled linearly to a scalar-isovector meson
field. We find that there exist reasonable values of the coupling constant
g (~4) and the source radius R (^0.3 fm) for which the strong coupling
approximation is valid. The lowest lying collective excitation of the
dressed nucleon is a rotational isospin mode with isospin i. If we allow
an intrinsic isobar excitation of the source (bare A) the strong coupling
approximation is valid for significantly smaller values of the coupling
constant or larger bag radii. In that case we find a bare A component in
the dressed nucleon of 36%. Meson nucleon scattering in this model has
been investigated numerically. A paper on this work has been submitted to
Phys. Rev. D. These results are encouraging. They justify the more
elaborate calculations required to treat the coupling of the pion field to
a little chiral bag with intrinsic excitations.
h. Monte Carlo Method for Chiral Bag Models (B. D. Day)
In chiral bag models of the nucleon, the meson field is coupled
to a static nucleon source with spin-isospin degrees of freedom. Various
approximation methods have been applied, and it is desirable to test their
accuracy. By putting the field on a spacetime lattice, the problem can be
formulated in terms of a path integral. Treating the path integral by the
Monte Carlo method would give reliable results to be compared with
approximate calculations. A possible problem is that the coupling to the
spin and isospin of the nucleon causes the integrand to be non-positive-
definite in the Monte Carlo calculation, which could spoil its numerical
accuracy. This has been tested in a preliminary study using a one-
dimensional lattice. Systems with as many as 40 lattice spacings were
treated. No loss of accuracy was found in the Monte Carlo method, which is
favorable for application to the full spacetime lattice. However, further
technical problems, such as subtracting the vacuum energy of the lattice
without loss of numerical accuracy, must be overcome before interesting
calculations are possible.
139
B. VARIATIONAL CALCULATIONS OF FINITE MANY-BODY SYSTEMS
S. C. Pieper, R. B. Wiringa, A. R. Bodmer, and collaboratorsfrom other institutions
Two approaches to calculation of finite many-body systems wereinitiated in 1983. One aim is to develop Monte-Carlo techniques forvariational calculation of the ground states of large finite systems ofparticles, with the ultimate aim of treating nuclei with realistic nucleon-nucleon potentials. The second problem under study is a modern treatmentof the binding of hypernuclei by including complex AN and ANNinteractions. Specific problems are discussed in the following.
a. Ground States of Quantal Many-Body Systems (S. C. Pieper,R. B. Wiringa, V. R. Pandharipande,* J. G. Zabolitzky,t andU. Helmbrecht )
In the past 30 years, there has been much progress in the
computation of the ground--state properties of infinite quantum liquids such
as nuclear matter or liquid 4 He or 3 He. For given interactions, accurate
calculations of the ground states of three- or four-particle systems have
also been made. However there has been relatively little work on quantum-
mechanical calculations of large (more than four particles), but finite,
systems of particles interacting with given potentials. We have begun to
develop Monte Carlo techniques for the computation of the ground state
properties of such systems. At Argonne and Urbana we are performing
variational calculations which give an upper bound for the ground-state
energy while Green's function Monte Carlo (GFMC) calculations are being
used at Bochum and Cologne. The latter method gives (up to statistical
errors) the exact ground-state energy and density distribution but requires
much lengthier calculations; these calculations are not possible on the
computers available at Argonne.
We have started by writing programs for droplets of liquid 4 He.
This is a simple system since we do not have to consider the complications
of spin degrees of freedom and antisymmetrization. Also the He-He
potential is a function of just the inter-atomic distance and the three-
body potential is weak enough to be ignored. The next case to consider is
*University of Illinois, Urbana, Illinois
tUniversity of Cologne, Cologne, Germany.
(Ruhr University, Bochum, Germany.
140
that of droplets of liquid 3 He. Here we will have to deal with spin and
antisymmetrization; however, the potential remains simple. Finally we hope
to be able to do useful calculations for nuclei using realistic (and hence
complicated) nucleon-nucleon potentials.
Although the liquid He droplet computations may be considered as
warm-up exercises for the calculation of nuclei, this work is interesting
in itself. The binding energies and radius parameters of the droplets may
be expanded as power series in N- 1 1 3 , where N is the number of atoms in a
droplet. The resulting series appear to be qualitatively different from
the results of the hydrodynamical approximations currently being used in
ne tron-star calculations. The extrapolation of such series to N= may be
compared with the infinite liquid calculations to learn something about the
reliability of the extrapolations used to find the "experimental"
properties of nuclear matter. It also appears that these series may give
the best available values for the surface energy of infinite liquids for a
given potential; there have been very few direct calculations of this
quantity.
b. Monte-Carlo Variational Calculations of 4He Droplets(S. C. Pieper, R. B. Wiringa and V. R. Pandharipande*)
A program for Monte-Carlo variational calculations of droplets
of 4He has been completed and is being used. In these calculations a
variational wave function containing one-, two-, and three-particle
correlations is used. The ground state energy is then a 3N-dimensional
integral, where N is the number of atoms in the droplet. The integral is
done by the Metropolis method. Because this is a variational calculation,
the parameters of the correlation functions must be varied until the
minimum ground state energy is found; this energy is then an upper bound on
the correct energy. We have already made calculations for 4 < N < 240 and
are planning calculations for N 700. The results for N < 100 can be
compared with the GFMC results and are found to le about 3.5% too high on
average.
*University of Illinois, Urbana, Illinois.
141
0.02
Io .
IZI 0.0!
n
I I v I I I I II I I I I IIIUI I I I I I -Y
-N
40- 20
84 8112 240
3
4 8 12 16
728
J L I1 *l
20 24
Fig. 111-4. Density profiles of droplets of 4He as computed by GFMC(solid curves) and variational Monte Carlo (dashed curves). The
curves are labeled with the number of atoms in the droplet.
Most of the computer time for these variational calculations is
used in calculations of only moderate statistical accuracy in which the
parameters of the wave function are varied in an effort to locate the
minimum energy. Because our wave functions have 10 to 20 parameters, and
because the statistical errors in two Monte Carlo calculations can result
in an erroneous conclusion as to the best parameter set, this process can
be quite painstaking. To help alleviate this, we have derived integral
expressions for the first and second derivatives of the energy with respect
to the variational parameters. These integrals can be evaluated in the
random walk used to compute the energy and thus we can predict an improved
set of parameters (or recognize that we are at the best set) in about the
same time that it takes to evaluate the binding energy (see Fig. 111-4).
V l 1 l 1 7L 1 1 _
rI
142
c. S-shell Hypernuclei and A-nucleon Interactions (A. R. Bodmer,J. Carlson,* and Q. N. Usmani*)
We are making variational calculations of the binding energies of
the s-shell hypernuclei: H, AH and 4He, He. In contrast to earlier
calculations we include tensor 2-body and 3-body forces, and calculate the
energies of the excited J=1 states of AH and He. Furthermore we use
semiphenomenological 2-body AN and 3-body ANN interactions with shapes
based on two-pion and one-kaon exchange mechanism. The variational
calculations use the techniques and nuclear wave functions developed by the
Urbana group of V. R. Pandharipande and collaborators; in particular the
appropriate 2- and 3-body correlations are included.
So far our calculations have been mostly with central AN
potentials for AH and Ae. A distinctive feature of our approach is to
determine the effective 2-body AN (s-state) interactions from the 2-body
scattering data and from VH but not from the heavier hypernuclei for whic"
many-body-force effects may be important. Our preliminary results indicate
these AN potentials to be only slightly spin dependent, consistent with
earlier investigations, and to give a reasonable ground state energy
for AHe, again consistent with earlier results, but to give too small
excitation energies for the J=1 states. These preliminary results
thus indicate that the splitting between the ground and excited states of
the A=4 hypernuclei is due to 3-body ANN forces or some other many-body
modification of the AN interaction (such as suppression of the AN-EN
coupling as proposed by B. F. Gibson and D. R. Lehman). Our future
calculations should help to clarify this situation. We have also been
preparing for calculations of charge symmetry breaking effects in 4and 4He where there are problems of long standing involving the size of
Coulomb-nuclear interference effects and of the spin dependence of the AN
charge-symmetry breaking interaction. We have also been preparing for
calculations of 5He. A long standing problem has been the overbinding
of AHe with 2-body forces (such as ours) which fit the 2-body scattering
data and the ground state energies of AH and AH, AHe. The inclusion of the
tensor components in the AN and ANN forces as well as inclusion of
"dispersion" type ANN forces should help to clarify this problem.
*University of Illinois, Urbana, Illinois.
14 3 //44
d. Alpha-Cluster Calculations of ABe and 'A Be (A. R. Bodmer,Q. N. Usmani,* and J. Carlson*)
We are making variational calculations of the hypernucleus ABe
and the double hypernucleus AABe assuming 2ac-A and 2c-2A cluster structures
for these hypernuclei, respectively. Earlier variational calculations
(including those of A. R. Bodmer and S. Ali) indicate that such cluster
models probably give a very good description of these hypernuclei. Such
cluster calculations then enable one to make quite reliable calculations of
the energies of these hypernuclei with fitted a-a and a-A potentials and
additionally some assumed AA potential for 10 Be. A reexamination of these
hypernuclei using such cluster models is timely because of improvements in
variational techniques of calculating few-body systems, in phenomenological
a-a potentials and also in the hypernuclear data. In particular 3Be is
currently perhaps the most reliably established AA hypernucleus, and its
analysis will therefore provide crucial knowledge of the AA interaction.
Also the binding energies of AHe and ABe are known more accurately than at
the time of the earlier calculations. Good calculations of Be are a
prerequisite for reliable calculations of AABe, as well as being of
interest in their own right. We have so far made variational calculations
of ABe for several available phenomenological c-a potentials and for a-A
potentials whose strengths are fitted to the binding energy of WHe and
whose shapes are obtained by folding effective AN potentials (obtained by
use of the Moszkowski--Scott separation method) into the c-particle density
distribution. It seems significant that we find ABe to be consistently
somewhat overbound (by about 0.5 MeV), consistent with the overbinding
of 5He and of a A in nuclear matter when central AN forces are used. We
are considering 3-body ANN dispersion type forces to see whether these will
account consistently for both the overbinding of 5He and Be. The
variational procedures for calculations of 0Be have been developed. We
shall use a two-pion exchange shape for the (singlet) AA potential, whose
strength will then be determined by the variational calculations for ABe
from the experimental value of the binding energy of 3Be.
*University of Illinois, Urbana, Illinois.
145
C. NUCLEAR SHELL THEORY AND NUCLEAR STRUCTURE
D. Kurath, R. D. Lawson, and others
Our principal concern is to identify nuclear structure effects inthe results of current experiments. Interpretations were obtained for highspin states excited in heavy-ion reactions and for nuclear states prominentin inelastic scattering of pions, electrons,and protons. A major effort isbeing directed toward understanding the effect of including the A degree offreedom in structure calculations. The analysis of inelastic excitation bypions is also being extended by including effects of recoil.
a. High Spin States in 9 1 Tc (A. Amusa* and R. D. Lawson)
High spin states and their decay mode have recently been observed
in 9 1 Tc. In order to check the consistency of the tentative spin
assignments we have carried out a shell model calculation for this
nucleus. 3 8Sr50 was assumed to be a doubly closed shell core and the five
valence protons and two neutron holes in 23Tc48 were assumed to occupy the
2p1/2 and 1g9/2 single particle states. The residual two-body interaction
was taken from the work of Serduke, Gloeckner and Lawson. The shell-model
results support the experimental angular momentum assignments.
b. The 6 States in 2 8 Si (A. Amusa* and R. D. Lawson)d/ 2 + [d/ 2 7/2 6-
Experimentall, inelastic electron, pion and proton scattering to
the yrast (6~,l) state all indicate that the cross section should be
approximately 30% of the (d5/2)1 2 + (d5/2
1 1f7 /2) value, while the pion and
proton data to the yrast (6~,0) state yield an even smaller value, ~15%.
Stripping finds C2S = 0.24 and 0.19 for these T=O and T=1 states,
respectively, that is about 1/2 the pure configuration value. In addition,
the value of B(M1) between these two 6 states has been measured and is
(2.8 0.4)WN, where 1N is the nuclear magneton. This is only about 20% of
the (d 5 /2,f7/ 2 )-model value of 14.439 uN. We have carried out calculations
using the entire (d5/2 ,s1/2) model space for the 0+ ground state, and for
the 6 states the same (d 5 / 2 ,s 1 / 2 ) model space was used with at most one
nucleon allowed in f7/2. Two different (d5/2,s1/2) interactions that fit
the normal parity states near A = 28 were used and the ds-f 7 / 2 mat. .x
elements were calculated using the Schiffer-True potential. As shown in
Table IIP-Z a substantial decrease in the predicted cross sections and
146
transition rate are obtained. The calculations suggest that when some
aspects of the d3/2 level are included, theory and experiment may be
brought into agreement without the introduction of non-nucleoni degrees of
freedom. This work has been submitted for publication in Physical Review
Letters.
Table III-2. All 6 states in 28Si predicted to have eitherinelastic scattering strength, R, or spectroscopic strength, Q, greaterthan 5% of the pure (d5/2,f7/ 2) sum rule value. E is the predictedexcitation energy of the state and T its isospin. The value of B(Ml)connecting the yrast (6 1) and (6_,0) states is given. The calculationshave been carried out for two different (d5/2 ,s1/2) interactions.
WMHG Interaction Modified Surface Delta
E T R Q E T R Q
11.576 0 0.258 0.412 11.576 0 0.389 0.49512.818 0 0.135 0.190 11.918 0 0.065 0.07813.020 1 0.522 0.737 12.765 1 0.585 0.68914.108 0 0.101 0.162 13.952 0 0.084 0.04414.845 1 0.058 0.138 14.050 0 0.131 0.06715.143 0 0.136 0.120 14.571 1 0.037 0.05015.409 0 0.037 0.078 14.721 0 0.023 0.06816.327 1 0.053 0.019 15.153 0 0.043 0.06418.474 1 0.058 0.008 15.764 1 0.157 0.133
16.888 1 0.038 Q.056B(Ml; (6-,1) + (6-,0)) 6.47 PR8.32
c. Con ributiog of Giant Dipole State to Coulomb Excitationof Li and Li (F. C. Barker* and R. D. Lawson)
In Coulomb excitation of a nucleus, the direct E2 excitation of
the final states may be modified by interference with the two step process
involving virtual El excitation of high lying states in the giant dipole
region followed by El decay to the final state. To estimate this
contribution one must know the ratio of the matrix elements between the
initial and final states of the E2 operator compared to the square of the
El operator. To compute this ratio reliably it is not sufficient to
introduce an effective charge but instead one must consider configuration
mixing explicitly. We obtained magnitudes for the admixed states by
*Australian National University, Canberra, Australia.
147
projecting states of good angular momentum frn deformed Nilsson
orbitals. In this way we included excitations from the is to the (2s,ld)
shell and from the ip to the (2p,lf) levels. In first order perturbation
theory the amount of the mixing depends on a single parameter, AE, the
energy difference between the unperturbed and admixed states. QE was
chosen to fit the observed quadrupole moment of Li and with this choice
the predicted B(E2) values for 6Li and 7Li agree with experiment. Values
for the square of the El matrix element are being calculated.
d. The Effect of the A(1236) on the g-factor of Nucleons (R. D. Lawson)
The effect of including the A degree of freedom in the nucleus
has been examined. In first order perturbation theory we have shown that
the main effect on magnetic dipole properties of replacing a nucleon in the
nucleus by a A is to give a renormalization of the g factor of the valence
nucleons. In the meson exchange model the (NN)++(NA) transition potential
is the sun of a central spin dependent and a tensor interaction. We show
that the main effect of the central interaction can be taken into account
if one adds an effective operator 2gs T3 . For the tensor interaction
the main effect is an added operator g [a x Y2]1 yT 3. When the quark
model phasing between the central and tensor parts is used we show that
these two interactions contribute with opposite sign for magnetic moments
leading to a small change in u. For Ml transitions they come in with the
same sign and reduce B(M1) values by 20--30%. Numerical values for the g-
factors are given in Table 111-3. This work has been accepted for
publication in Physics Letters.
e. Beta Decay of 16C(O+) to 1 6N(0-) (D. Kurath)
In connection with a recent experimental measurement of this beta
decay, a shell-model calculation was carried out in the lowest order
(lp~1,2sd1 ) and (1p-2 ,2sd2 ) space. The calculated transition probability
is about (1/6) the value for a pure 2s1/2+lp1/2 transition, which is much
stronger than the observed value.
148
Table 111-3. Values of the g factors in nuclear magnetons fornuclei near the closed shells A16, 40, 90 and 208. The numberical resultsare for the transition potential of Smith and Pandharipande and thecontribution of the central and tensor parts are 1 s ed separately.Oscillator wave functions rere used (4-exp - 1/2cr ) with a= 0.598 fm~for the 0 shell, .563 fm for tie is and Od orbits, 0.497 fm- near A=40,0.453 fm at A90 and 0.3996 fm for Pb. If the quark model values areused in both the M1 transition operator and potential, the results must bemustiplied by 0.613. The effective M1 operator has
(Ml) = (3/40)1/2 {l(1) 3s(0) + T3 + g
+(n/2)1/ 2 (g(l) T3 + xg(0)[ 21y
P entral tensorA Orbit gs(g() (1) (0) (1 g(O)
is -0.244 0.0 0.0 0.0 0.0 0.0
16 Op -0.193 0.0 0.496 0.0 0.0 0.0
Od -0.175 0.0 0.471 0.0 0.0 0.0
is -0.302 0.0 0.0 0.0 0.0 0.0
ip -0.304 0.0 0.384 0.0 0.0 0.0
40 Od -0.265 0.0 0.368 0.0 0.0 0.0
Of -0.244 0.0 0.421 0.0 0.0 0.0
ip -0.418 -6.37 x10-4 0.323 -0.004 -0.002 7.47 x10- 4
90 Of -0.371 -1.13 x10-3 0.298 0.005 -0.004 1.33 x10-3
Og -0.331 -9.11x10-4 0.354 -0.005 -0.003 1.06 xlO-3
2s -0.525 0.0 0.0 0.0 0.0 0.0
2p -0.502 -2.93 x10-5 0.282 -0.026 -0.001 2.97xl0-5
ld -0.509 -2.53 x10-5 0.241 -0.018 -0.003 5.02 xl0-5
208 if -0.473 -4.14 x10-5 0.280 -0.028 -0.002 4.45 x10-5
ig -0.438 -9.35x10-6 0.292 -0.038 -0.001 2.47x10-6
Oh -419 1.70 x10-6 0.241 -0.027 -0.004 1.83 xl0-5
01 -0.372 -7.13 x10-5 0.279 -0.037 -0.003 8.27x10-5
14 9! b'
f. Analysis of Inelastic Scattering of Pions (T.-S. H. Lee andD. Kurath)
We have continued analyzing results from experiments of inelastic
scattering of '1 at pion energies near the (3,3) resonance, using a
combination of a DWIA reaction calculation with input results from shell
model calculations for particular states. The results for the 14N
experiment of the Argonne group have been published) and the 11B results
were presented at the Amsterdam conference and are in preparation for
publication. Our conclusion that a few J(LS) multipoles dominate the
strong transitions has been substantiated.
While the strong J-il transitions arise from the (LS)=(10)
multipole, the spin dependent (LS)=(ll) multipole is of interest because it
has a different angular distribution which peaks at 00, and its
contribution is largely incoherent with the (10) case. Recent forward
angle experiments at LAMPF are seeking such transitions, so a shell-model
survey of the (LS)=(1l) strength distribution has been done for 12C
and 1 4 N. There is a much broader distribution in energy than was true for
the (10) multipole.
1D. F. Geesaman et al., Phys.Rev. C 27, 1134 (1983).
151
D. INTERMEDIATE ENERGY PHYSICS
The intermediate energy pion-nucleus interaction is dominated bythe formation of the A resonance. The importance of the A degree offreedom in determining low energy nuclear properties and various nuclearreactions at higher energies has also received considerable attention inrecent years. Our study of intermediate energy physics has long been aimedat developing a unified many-body approach which can describe the A-nucleusdynamics both at low and intermediate energies. This is achieved byextending our conventional nuclear many-body theory to include the A and rdegrees of freedom. A separable model of such a many-body Hamiltonian wasconstructed by Betz and Lee in 1981 and has been applied in 1982 tosuccessfully understand various aspects of the A-nucleus dynamicsexhibited in pion-nucleus reactions. In 1983, the model has been extendedto account for the meson-exchange mechanisms. The constructed model fitsthe most recent NN scattering phase shifts in the entire energy region upto 1 GeV. The model can be used to explore whether the meson exchangemechanism can accurately describe the A-nucleus dynamics involved in pion-nucleus interactions and in high-energy electron nucleus scattering.
Our DWIA model for pion scattering has been extended to includenucleon recoil effects and also to account for the possible effects due tothe A component in nuclear wave functions. This improved DWIA model willbe used in 1983-84 to further explore nuclear structure in pion inelasticand charge-exchange scattering.
In 1982, we also investigated high energy electron scatterngfrom nuclei. The cross section of producing hypernuclei by the (e,e'K )reaction is predicted to be achievable by the proposed few GeV electronaccelerator. Work has also been done to investigate the A excitation inelectron scattering from light nuclei.
a. Phenomenological Many-Body Hamiltonian for Pions, Nucleons,and A Isobars (T.-S. H. Lee)
To study both the intermediate energy pion nucleus interaction
and the A degrees of freedom in nuclei, we have constructed a many-body
Hamiltonian for pions, nucleons and A isobars. The basic mechanisms of the
model consist of: (a) a two-body interaction VO between all two-baryon
states NIT, NA and AA, (b) a wN A vertex interaction in the resonant IN(3,3) channel, and (c) a two-body interaction V N in other iN channels.The interactions are determined by fitting the IN phase shifts up to 300
MeV and NN phase-shifts up to 1 GeV. A separable model of such a
Hamiltonian has been used to study various aspects of the A-nucleus
dyruwics (see Sec. D.b. and D.c.). If the interaction VO is not separable,
such as that derived from the meson-exchange mechanism, the correct
treatment of NN three-body branch cut at E > 300 MeV comprises the major
152
numerical problem in practice. In 1983, we have successfully developed a
practical numerical method to overcome this difficulty. The method has
been applied to explore the consequences of various meson-exchange models
in describing NN scattering up to 1 GeV. The major results are: (a) the
dynamical effects due to the vertex interaction N A and the NN interaction
in the NN channel are important at E > 400 MeV and (b) the meson-exchange
model of the Paris potential can describe reasonably well the most recent
NN phase shifts up to 1 GeV. A paper describing the method and the results
has been submitted for publication in Physical Review Letters. The
calculated p-p phase-shifts are compared with the Arndt's phase shifts in
Figs. 111-5 and 111-6. Our goal in 1983-84 is to explore the consequences
of the meson-exchange model in describing NN polarization cross sections,
and to investigate the problem of dibaryon resonance by also considering
short-range quark-gluon dynamics.
b. A Microscopic Study of A-Nucleus Dynamics (T.-S. H. Leeand K. Ohta*)
In the one-hole line approximation, the self energy of A
propagation in nuclear matter is calculated from the separable model
Hamiltonian for Tr, N and A constructed by Betz and Lee. In the local
density approximation, the calculated A self energy corresponds to the
strength of the A-nucleus potential which is determined phenomenologically
in the A-hole doorway model of pion-nucleus scattering. We find that our
calculated strength of the central potential is on the average about 80% of
the empirical one. However, the calculated spin-orbit potential is much
smaller than that of the A-hole model. We also find that pion absorption
through the NA S wave only accounts for about half of the total
absorption. The sum of the other partial waves is found to be equally
important. A paper describing our study has been published in Phys. Rev. C
25, 304 (1982). In 1983-84, we plan to reinvestigate this problem with the
newly constructed meson-exchange model Hamiltonian described above.
*Massachusetts Institute of Technology, Cambridge, Massachusetts.
153
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c. Absorption of Pions by the A=3 Nuclei (T.-S. H. Lee andK. Ohta*)
Within the separable model Hamiltonian of Betz and Lee, we have
studied the absorption of pions by 3He. Keeping only the intermediate
states involving at most one pion or one A and neglecting two nucleon
interactions in the TrNNN channel, we express the absorption amplitudes in
terms of a three-body amplitude defined in the coupled NNNONNA subspace.
The resulting three-body equation has been solved by using the iteration
method due to Kloet and Tjon.
Our first important result is that the strong isospin dependence
observed in pion absorption on 3He can be described by tite two-body
mechanism wNN - AN - NN. Our results for 165-MeV pion energy is shown in
Fig. 111-7. The effect of the three-body mechanism is also calculated but
found to be negligibly small. The AN - NN dynamics consistently determined
from NN inelasticities is shown to be essential to understand the isospin
dependence. A paper describing this result has been published in Phys.
Rev. Lett. 49, 1073 (1982). Our prediction of the angular correlation of
the 3He(ir+,pp) reaction at 75 MeV has been confirmed by a recent
measurement at TRIUMF. In 1983-84, we plan to complete the analysis of
this new data as well as the data to be obtained at LAMPF. Our objective
is to explore the extent to which the pion absorption by nuclei can be
described by the two-body mechanism WNN-NA-NN.
d. Electroproduction of A From Light Nuclei (T.-S. H. Lee andK. Ohta*)
The dominant mechanism in (e,e') on nuclei when the energy
transferred to the nucleus is about 300 MeV involves excitation of a
nucleon to the A state. The kinematic conditions of A creation by the
virtual photon are quite different from those in the pion-nucleus
interaction. Since the virtual y interacts weakly with the nuclear medium,
the A can be produced throughout the nuclear volume, whereas the pion
produces A's mainly on the nuclear surface. Furthermore if the incident
electron energy is several GeV, one can produce very fast off-shell A's
with momenta of many GeV/c. The A produced in the n-nucleus interaction is
*Massachusetts Institute of Technology, Cambridge, Massachusetts.
156
'-n 1000- -
} 010 0 (7r,+ p p )
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440 480 520 560 600p1 (MeV/c)
Fig. I1I-7. Momentum spectra of He(r ,pp) and He(7r,np) at 01 = 550and 02 = 1000 are compared with the data of ANL [Phys. Rev. Lett.47, 895 (1981)].
157
mainly on-shell with momentum about 0.3 GeV/c. Therefore the (e,e') study
can examine the dependence of A-nucleus dynamics on the nuclear density and
on the A momentum. We are studying the electroproduction of A from the
deuteron and 3He by adding the vertex interactions yN-A and YN«N to our
many-body Hamiltonian for IT, N and A (described in Sec. IV.A.a.). Partial
wave analysis needed for carrying out the calculations of d(e,e') has been
completed. A computer program for numerical calculation is being
developed. The calculations for 3He are closely related to our study of
pion absorption by 3He (Sec. D.c.) and can be carried out by using the same
numerical method. We expect to obtain results in 1983-84. Our objective
is to explore the usefulness of the proposed few GeV electron accelerator
in the study of A-nucleus dynamics.
e. A Nonstatic DWIA Model for Pion Scattering (T.-S. H. Lee)
Our DWIA code has been widely used by many groups to interpret
pion-nucleus inelastic scattering data. The program has now been extended
to include nucleon recoil effects in the rN t matrix. This improvement of
the DWIA model is needed to account for the contribution from the
transverse nuclear form factors which dominate some nuclear excitations due
to pions. The model has also been extended to account for the possible
effect of the A component in nuclear bound state wave functions, assuming
that the IN + A transition can be related to the irN + IN interaction in
the quark model. In 1983-84, we will use this improved DWIA program to
further explore nuclear structure effects in pion inelastic and charge-
exchange scattering.
f. Production of Hypernuclei by Few GeV Electrons (T.-S. H. Leeand J. P. Schiffer)
In the one-photon-exchange approximation, we have estimated the
cross section of the production of hypernuclei by (e,e'K+) reactions. The
angular correlations and energy dependences of 12C(e,e'K+) reaction have
been calculated for various kinematics of coincidence measurements. It is
shown that a few GeV electron accelerator is very efficient for carrying
out such a study. In Fig. 111-8 we show the calculated cross sections with
2-GeV electrons. The results are included in the ANL proposal of GEM to
the Department of Energy.
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g. A Model of Elastic and Inclusive P-Nucleus Scattering Above 500 MeV(J. A. Parmentola and H. Feshbach*)
In the impulse and closure approximations, we have developed a
coupled-channel model of p-nucleus scattering based upon the KMT expansion
of the optical potential to second order in the 2-body scattering
matrices. In this model, the inelastic channels are represented by a set
of effective channels. The essential idea of the method is to choose the
effective channel basis such that the infinite number of physical channels
can be approximated by a finite number of effective channels. In the
closure approximation, the inclusive cross section is obtained by summing
over all physical channels, however the effective channel basis provides an
equivalent and economical evaluation of this quantity.
We have applied this model to P- 4 He scattering at 1 GeV and we
have compared our results for elastic scattering to the method of
calculation of Feshbach, Gal, and Hiifner with the same input data. The
advantage of our method is that it is economical and numerically exact,
while the FGH method is approximate and difficult to improve. The
comparison of the two methods reveals significant discrepancies. We are
currently trying to track down the origin of these discrepancies.
*Massachusetts Institute of Technology, Cambridge, Massachusetts
161
E. HEAVY-ION INTERACTIONS
S. C. Pieper, M. J. Rhoades-Brown,*, A. R. Bodmer, and others
Our theoretical effort in heavy-ion interactions has been
concerned with two kinematically different regions. One is concerned with
low energies, up to several times the Coulomb barrier. Here we havedeveloped a large program, Ptolemy, for the coupled-channels computation ofinelastic scattering. This program is now essentially complete, and is inuse by both theorists and experimentalists at a number of locations inaddition to Argonne. Two current examples of such calculations are givenbelow.
The second kinematic region deals with collisions at energiesabove about 100 MeV/nucleon where one may encounter conditions of highdensity and temperature at which new states of nuclear matter may exist.We initiated and are continuing classical-equations-of-motion (CEOM)calculations of high-energy heavy-ion collisions. The CEOM method is acompletely microscopic but classical approach whose essence is thecalculation of all nucleon trajectories using a two-body potential between
all pairs of nucleons. The unique feature of this approach is that itincludes finite-range interaction effects (in particular potential energyeffects) and hence does not assume that nuclear matter is a dilate gas asdo cascade calculations. On the other hand, in contrast to hydrodynamics,the CEOM approach is a microscopic one and does not assume localthermodynamic equilibrium.
*Oak Ridge ' tional Laboratory, Oak Ridge, Tennessee.
a. Analysis of 2 8Si+2 8Si Scattering (S. C. Pieper andM. J. Rhoades-Brown*)
Within the last few years, extensive data on the elastic and
inelastic scattering of 28Si from 28Si have been measured at Argonne and
Brookhaven. Inelastic channels up to the mutual excitation of the 4+ and
6+ states are resolved; in the vicinity of 900, channels such as the mutual
4+ ,4+ contain most of the cross section. We have attempted to analyze this
data with large coupled channels calculations. Because of the strong
deformation of 2 8 i 2 ~~ -0.4) we find it necessary to include A = 0, 2, 4
and 6 projections for both the projectile and target of the deformed
potential. Our biggest calculations contain 169 coupled equations with
almost 25,000 coupling- terms. We find that with reasonable potentials we
can reproduce either of the two qualitative features of the data: (1) the
smooth decay of the elastic differential cross section out to about 700 or
*Oak Ridge National Laboratory, Oak Ridge, Tennessee.
162
(2) the very strong excitation of the high-lying mutual excitation channels
at 90*. However we have not found one potential that predicts the
qualitative features of the data over the entire angular region. Work on
this problem is continuing.
b. Analysis of 160 and 180 Scattering from 54Fe (S. C. Pieper andS. Landowne*)
With an 160 projectile, the backwards excitation function for the
first 2+ state of 5 4Fe shows a pronounced Coulomb-nucleon interference
minimum. However this minimum is filled in when 180 is used as the
projectile. We attempted to analyze this difference by first using the
160+54 Fedata to determine optical parameters for the 1 6 0+5 4 Fe system.
The resulting potential was then used as a core potential for the
1 80+54Fe system with the effect of the two additional neutrons in 180 being
accounted for by a n+5 4 Fe optical potential. These potentials were used in
coupled-channels calculations that, for the 180 projectile, included
excitation of the 2+ states of 180 and 54Fe and mutual excitation. Good
fits were obtained to both the elastic and inelastic 160 data, but the
resulting 180 potentials did not accurately predict the 180 elastic cross
sections, nor did they predict the filled in minimum of the inelastic
scattering. Work on this problem will be continued in Munich this summer.
*University of Munich, Munich, W. Germany.
c. Extension of the CEOM Calculations (A. R. Bodmer and C. N. Panos*)
We have been developing the CEOM calculations to allow for Pauli
blocking effects in the one-body phase space. This is being done by
incorporation of probabilistic elements in the scattering using appropriate
binning of the phase space. Developments so far look encouraging but will
require more efficient or faster calculations of the many-body
trajectories. Inclusion of Pauli blocking effects would make the CEOM
approach more applicable to higher densities and especially to lower
*University of Ioannina, Ioannina, Greece.
163//16+
energies, namely in the range of about 50--200 MeV/nucleon where there is
currently no suitable microscopic description. We have also been
considering momentum dependent 2-body potentials together with other
procedures in order to obtain more satisfactory binding and nucleon-nucleon
scattering properties, in order to allow study of a larger range of
projectile and target nuclei, and also more realistic equations of state.
165/4(L;
F. OTHER THEORETICAL PHYSICS
a. Angular Momentum Near Solenoids and Monopoles (Murray Peshkinand Harry J. Lipkin)
Interest in some of the quantum mechanical consequences of
electromagnetic angular momentum has recently been renewed by two unrelated
developments. Firstly, it has been appreciated that the quantum mechanical
constraints on the scattering of an electron by a magnetic monopole at
near-zero impact parameter have important implications for the nature and
mass scale of the monopole. Secondly, there has been an interesting
suggestion that a composite made of an electron and an infinitely long
solenoid may have unusual statistics because it can have nonintegral
orbital angular momentum. We have examined the nature and location of the
electromagnetic angular momentum which arises from the Poynting vector
produced by crossing the electric field of the electron with the external
magnetic field. We show that proper inclusion of the solenoid's return
flux removes the nonintegral orbital angular momentum, and that neglect of
the return flux by making it disappear at infinity leads to unphysical
results. We also show that the origin (in the relative coordinate) must be
excluded for kinematical reasons due to angular momentum quantization when
an electron is scattered by a fixed monopole. This work has been published
in Physics Letters 118B, 385 (1982).
b. Triplet Correlations in Spin-Aligned Deuterium (Robert M. Panoff)
The question of the stability of spin-aligned deuterium was
investigated using a wave function which incorporated the possibility of
three-particle correlations. An improved variational Monte-Carlo code was
used, and at low density it was found, as expected, that very little
additional binding (0.01 K) resulted from the added correlations. The code
was expanded to allow the calculation of the resultant one-body density
matrix.
IV. THE SUPERCONDUCTING LINAC
R. Benaroya, J. M. Bogaty, L. M. Bollinger, R. C. Pardo,
K. W. Shepard, G. P. Zinkann, J. Aron,* B. E. Clifft,*
K. W. Johnson,* P. Markovich,* and J. M. Nixon
INTRODUCTION
The activities concerned with advancing the technology of thesuperconducting heavy-ion linac now have three major components. One isthe specific task of completing and refining the prototype superconductinglinac that functions as an energy booster for heavy ions from the tandemelectrostatic accelerator. The second part consists of continuinginvestigations of various aspects of superconducting rf technology, some ofwhich are of fairly general interest for accelerator technology. The thirdundertaking is the line-item project to extend the present tandem-linacaccelerator into a substantially larger system called ATLAS.
All parts of the superconducting linac program are jointlysupported by the Chemistry and Physics Division.
*Chemistry Division, ANL.
169/)'70
A. PROTOTYPE HEAVY-ION SUPERCONDUCTING LINAC
This project, started in mid-1975 and now completed, has beenconcerned with the design, construction, installation, and testing of asmall superconducting linear accelerator (linac) to serve as an energybooster for heavy-ion beams from the FN tandem accelerator. The principalobjectives of the project have been to develop a new accelerator technologyand to build the prototype for a heavy-ion energy booster that can be usedto upgrade the performance of any tandem accelerator. The overall designis highly modular in character in order to provide maximum flexibility forfuture modifications and/or improvements. The last two resonators of theplanned 24-resonator system were installed in 1982.
The booster linac is now complete in all respects. Its mainfeatures have been outlined in previous Annual Reviews. Some effort isstill being devoted to perfecting various subsystems of the accelerator, asoutlined in Sec. V, and this effort is resulting in a machine of excellentreliability. However, our developmental effort is now being devoted mainlyto the ATLAS project.
By now, the booster has been used extensively ('10,000 hr) toprovide beams for nuclear-physics research. This operational experience issummarized in Sec. V of this document.
The booster will continue to be used in its present form untillate 1984 or early 1985, when it will be incorporated into the ATLASfacility.
171
B. INVESTIGATIONS OF SUPERCONDUCTING-LINAC TECHNOLOGY
This program includes several investigations of applications ofsuperconducting technology to the acceleration of heavy ions. At thepresent time, the choice of work is guided principally by the urgentdevelopmental needs of the heavy-ion booster and especially for ATLAS.Most of this work is included within the following topics: (a)superconducting accelerating structures, including studies of the phenomena
that limit performance, (b) time-of-flight technology for pulsed beams,and (c) superconducting magnets for heavy-ion beams.
1. Superconducting Accelerating Structures
K. W. Shepard, G. P. Zinkann, and P. Markovich*
The development of superconducting accelerating structures forheavy-ion acceleration is proceeding on a broad front. This work includes(1) the development of the new class of resonator for use in ATLAS, (2)efforts to improve the performance of the two existing classes ofresonators, and (3) the development of a new slow-tuner controller.
a. The ATLAS Resonator
For ATLAS it is desirable to have a resonator that is optimum for
an ion velocity that is substantially higher than the present S = 0.105
unit. After a thorough design study, it was concluded that the best choice
for our needs would be a split-ring resonator operating at 147.5 MHz (3/2
times the present frequency) in the same housing as the present 0 = 0.105
unit. This choice maximizes the acceleration of ions with S = 0.16. By
optimizing the shape of all parts of the drift-tube assembly, it is
expected that the accelerating field will be increased. This type of
resonator and its older brothers are pictured in Fig. IV-1.
As was reported last year, a first prototype resonator was
completed and partially tested in early 1982. Further tests showed that
the unit had a good Q at low fields, but the maximum achievable
accelerating field was limited to about 2 MV/m, less than half of the
expected value. Although the test results were inconclusive, the data
strongly suggested that at least two of the welds in the structure were
defective. However, efforts to repair the welds were unsuccessful.
*Chemistry Division, ANL.
jll
Fig. IV-l. The three classes of resonators to be used in ATLAS. On the left and right, respectively,
are the proven S= 0.105 and S = 0.060 units that operate at 97 MHz. The new ATLAS unit, designed
for 6= 0.16 and 145.5 MHz, is in the middle. All three units have housings with an inside diameter
of 16 inches.
11
f
1
s
1'
173
In view of the problems with the first prototype resonator, the
fabrication of a second prototype was started in June 1982. Considerable
effort was devoted to control of the quality of the welding process and to
an x-ray examination of each weld. This effort delayed the fabrication
schedule but has at least resulted in welds that appear to be of superior
quality.
The second prototype resonator was completed in January 1983, and
testing started immediately. The low-field Q of the unit is found to be
high. Also, it can be operated stably at an accelerating field well above
4 MV/m, thus indicating that the welding problem experienced with the first
unit has been solved. However, a drop in Q that appears to result from
electron loading sets in at a relatively low field, and consequently the
useful accelerating field is only about 3.3 MV/m, about 30% lower than was
expected. The cause for this problem has not yet been identified.
Intensive work on the resonator is continuing.
b. Resonator Accelerating Field
During the past year the last resonators for the prototype linac
were completed and installed. Most of our recent resonators are of
excellent quality, but two of the low-S units have exceptional
performance. The best of these was operated at an accelerating field of 6
MV/m with a power loss of only 4 W and was operated stably at 8 MV/m. This
latter value of the accelerating field corresponds to a maximum surface
electric field of 39 MV/m, probably a record high value for this
quantity. The reason for the outstanding performance of the resonator is
not known, but the result is nevertheless judged to be important because it
proves that it is feasible to improve considerably the performance of our
other resonators.
c. Restoration of Performance
During the past year, some of the resonators in the prototype
linac had been in continuous use for more than three years, and the Q of
some units had degraded so much that they were not useful. Previously, we
174
had demonstrated that such units could be restored to their original
performance by disassembly and electro-polishing, but this procedure is not
entirely satisfactory because it is relatively time consuming.
Consequently, we have tried the much simpler procedure of ultra-sonic
cleaning and rinsing the surfaces with water and several organic
solvents. It was found that this technique restores the performance of the
unit almost completely, both with respect to Q and maximum accelerating
field. This result is interesting not only because it establishes a simple
method for restoring the performance of long-used resonators but also
because it shows that the resonators do not suffer any fundamental
degradation in some 10,000 hours of operation.
d. Slow-Tuner Controller
(K. W. Johnson,* B. E. Clifft, and K. W. Shepard)
After several unsuccessful attempts, a new type of slow-tuner
pressure controller that meets all requirements has been developed and
thoroughly tested. It is now in use on all of the resonators of the
prototype linac and will be used in ATLAS. There have been no failures of
the new system during the six months that it has been in use on the
prototype linac.
2. Time-of-Flight Technology
R. C. Pardo, K. W. Johnson,* and B. E. Clifft*
The effort to develop time-of-flight technology as a major tool
in the control and use of the prototype linac has continued. The main work
during the last year has been the continuing effort to refine the energy-
measurement system that makes use of the phase difference between two beam-
excited resonators.
The validity of the concept involved in our energy-measurement
system was demonstrated several years ago. However, it turned out that its
electronic system was not able to respond properly to the confusion that
*Chemistry Division, ANL.
175
results when a resonator in the linac goes momentarily out of lock, and
consequently the energy-measurement system has not been much used. Now the
electronic problems have been eliminated, however, and the beam energy can
routinely be measured continuously and non-destructively with an accuracy
of about two parts in 104. Unfortunately, this capability is available now
only on the +190 beam line, which feeds the 60-in scattering chamber and
the magnetic spectrograph. In time, the capability will be extended to the
other beam lines.
3. Superconducting Magnets
a. Prototype Bending Magnet
Work on the prototype superconducting magnet has proceeded
vigorously during the past year. The coil has been rewound, the cryostat
fabricated, machining of the iron completed, and the system assembled.
Testing is expected to start in April 1983.
Although the magnet being developed is viewed as the prototype
for several possible applications, it has design characteristics that are
well matched to what is required of a beam-switching magnet in the ATLAS
experimental area, and the prototype itself may end up in this application.
b. Heavy-Ion Beam Splitting
In the ATLAS system, we expect to split the beam into two
components in the interface region between the present and the future linac
sections. Two different kinds of magnets are being studied for this
application: (1) a superconducting septum magnet and (2) a hybrid system
consisting of an iron magnet with a field-free region produced by a
superconducting super-tube. Both approaches appear to be attractive
solutions to a difficult technical problem but both also involve some risk,
since neither approach has been tried previously.
176
4. Near-Term Plans
Much of the effort in 1983 and 1984 will continue to be devoted
to problems that are closely related to the refinement of the present linac
and especially to the needs of ATLAS.
If necessary, work on the a = 0.16 resonator for ATLAS will be
given a high priority. At this time, it is too early to know exactly what
questions will be addressed, but if the experience with this new design is
similar to that with earlier resonators, there will surely be some problems
that need to be studied.
A related area that requires further work is the investigation of
the factors that limit the performance of resonators. Now that we have
three classes of resonators with somewhat different parameters, we expect
to see performance patterns that will suggest models to be explored.
A considerable effort will be devoted to superconducting magnets
during 1983 and 1984. In particular, the work will focus on the special
magnets to be used for beam separation in the 40*-bend region of ATLAS.
Since this area of work is little explored, it is likely to lead to new
paths that are as yet unforeseen.
By late 1985, the ATLAS linac will be assembled and a sizable
effort will need to be devoted to studying its characteristics. In
particular, matching the beam from the present linac into the ATLAS linac
may be time consuming initially and may require the development of new
diagnostic techniques. In any case, the characteristics of the new kind of
beam splitter will be thoroughly studied.
C. THE ATLAS PROJECT
The Argonne Tandem-Linac Accelerator System (ATLAS) is a heavy-
ion accelerator being formed by enlarging the booster linac and by adding a
large new target area, as shown in Fig. VI-2. The resulting system,
consisting of the existing tandem and a 7-section linac, will have a
performance that is approximately equivalent to that of a 50-MV tandem with
two strippers.
4FN TANDEM
TARGET AREA I
( F
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ADD\TION
H A TARGET
AREABOOSTER LINACLII
ACCELERATOR 40*O1 03 05CONTROL BEND 010 20 30 40 5
ROOM SCALE (feet)
Fig. IV-2. Layout of the ATLAS facility. The building areas shown in grey (dotted) and the
accelerator components shown fully darkened are being added by the ATLAS project.
178
ATLAS is aimed squarely at the needs of precision nuclear-
structure physics, providing beam energies up to 25 MeV/A, easy energy
variability, and beams of exceptionally good quality. The short-pulse
character of the beam will be emphasized so as to maximize its usefulness
for time-of-flight and other timing measurements. An unusual feature of
the facility is the capability of providing beams simultaneously for two
independent experiments without a loss of intensity to either.
The ATLAS project was authorized in the FY 1982 budget at a level
of $7.7 million, of which $4.0 million was appropriated in FY 1982, and the
remainder in FY 1983. The project started officially in January 1982 when
the initial funds were released. By the end of this reporting period
(March 1983), the project was about 40% completed.
The construction of the ATLAS building addition got off to a very
fast start and, because of economic conditions in the building industry,
this has probably resulted in a considerable savings in cost. The first
phase of construction, consisting of foundations and poured-concrete walls,
was started in May 1982 and completed in October. The remaining work
started in December 1982, and by the end of the present reporting period
the building superstructure is in place, the enclosure of the building is
nearing completion, and work on building services has started. We expect
to start occupying the new building before Christmas 1983.
One of the main technical objectives of the ATLAS project is to
add three linac sections that can effectively accelerate the relatively
fast projectiles produced by the booster linac. This required the
fabrication of 18 new resonators. Our present plan is to have the first 6
of these be of our proven S = 0.105 type in order to make it easy to match
the beam from the booster into the new linac. The other 12 units will be
of a new type that is optimum for ions with S = 0.16 and operates at an RF
frequency of 145.5 MHz, 3/2 times the frequency of the booster units. The
status of development of the new accelerating structure is summarized in
section VI.B.l.a.
Because the accelerator addition involved in ATLAS is closely
similar to the existing prototype linac, it was possible to start the work
on major components as soon as funds were released. Consequently, rapid
progress has been made. Cryostat fabrication is now largely completed, and
179// 0
one unit is expected to be ready for operation with installed resonators by
late 1983.
Unlike the booster linac, we plan to start operation of the full
ATLAS system only when all resonators are in place. Officially, this major
milestone is scheduled for April 1985, but obviously we are trying to beat
this schedule. In the meantime, the 24-resonator booster linac will
continue to be intensively used for research in the present experimental
area.
1811f/ 5$'
V. ACCELERATOR OPERATIONS
Introduction
This section is concerned with the operation of both the tandem-linac heavy-ion accelerator and the Dynamitron, two accelerators that areused for entirely different research. Developmental activities associatedwith the tandem and the Dynamitron are also treated here, but developmentalactivities associated with the superconducting linac are covered separatelyin Sec. IV, because this work is a program of technology development in itsown right.
183
A. OPERATION OF THE TANDEM-LINAC ACCELERATOR
The tandem-linac accelerator is operated as a source of energetic
heavy-ion projectiles for research in several areas of nuclear physics and
occasionally in other areas of science. The accelerator system consists of
a 9-MV tandem electrostatic accelerator and a superconducting-linac energy
booster that can provide an additional 20 MV of acceleration. Figure V-1shows the layout of this system, which will be operated in its present form
until the end of 1984, when it will be incorporated into the larger ATLASsystem. In both the present and future forms the accelerator is designed
to provide the exceptional beam quality and overall versatility requiredfor precision nuclear-structure research.
Some aspects of the technology of the superconducting linac are
discussed in Sec. IV.
1. Operation of the Accelerator
The tandem-linac has been operated routinely and effectivelyduring much of the past year as a research tool, mainly but not exclusively
for nuclear physics. Some statistics about the operation are summarized in
Table V-I, and representative beams that have been accelerated during the
past year are described by Table V-II.
A notable feature of the use of beams from the accelerator is theincreasing involvement of outside users, as indicated by the data of TableV-I. In particular, the running time allocated to outside users is
expected to increase from 35% in FY 1982 to 51% in FY 1983.
The overall quality of the operation has improved greatly duringthe past year, partly because of the technical improvements summarizedlater and also because of a change in the way in which the linac isoperated. In the first few years of operation, the beam user was
responsible for the operation during all but the day-time shifts. Thisarrangement was necessary in order to minimize costs, but it was
undesirable because it resulted in reduced running efficiency. The problemwas largely eliminated in May 1982 when qualified operator/engineers werescheduled to be present during the evening shifts. This added manpoweralso made it possible to expand the running schedule from five to six
twenty-four days per week, i.e., from Monday morning to Sunday morning.
Because of funding limitations in FY 1983, it has recently(February 1983) been necessary to reduce the running schedule back to afive-day week. Moreover, the accelerator will be shut down for at leastsix weeks in order to reduce operating costs. Since these reductions arein addition to the down times required for various accelerator-improvementactivities (including ATLAS), the total running time in FY 1983 is expectedto be considerably less than in FY 1982. This reduction is especiallypainful at this time because there is now an intense demand for runningtime and the superconducting linac is now an excellent research tool.
It is believed that it will be feasible to return to a six-dayper week operating schedule in FY 1984.
TARGET AREA I
A
C D
EF
G
A SSE MBLY
AREA
z 3z
ION SOURCE
PRE-TANDEMBUNCHER
ENERGY-MEASUREMENT MAGNETIC11 3 YSTEMSPECTROGRAPH
REFRIGERATORS 65" TRE
SCATTERING ARETI
CHOPPER REBUNCHER/
-STRIPPER DEBUNCHER
A B C D .. = , , --
BUNCHER PHASE LASER 18"
SERVIIF CES CHAMBER CHAMBERILIY
AcG NEUJT RON FA CI L ITY
CONTROLROOM DATAI
RECORDINGROOM
i-r 1
LASBRLAB T-0-F
CHAMBER
O 10 20
SCALE (feet)
Layout of the present tandem-linac facility. The experimental apparatus shown on the figure
is now all functional.Fig. V-1.
I
)i
185
Table V-I. Operation of the ANL tandem-linac heavy-ion accelerator.
Fiscal Year
1982 1983*
Distribution of Machine Time (hr)
Research
Tandem-Linac System 3,077 2,350
Tandem (stand alone) 437 180
Tuning 497 190
Machine Studies 397 600
Unscheduled Maintenance 714 450
Scheduled Shutdown 3,640 4,990
Total (1 yr) 8,760 8,760
Distribution of Research Time (%)
ANL Staff 65 49
Universities (U.S.A.) 26 40
DOE National Laboratories 2 2
Other Institutions 7 9
Total 100 100
Outside Institutions Represented
Universities (U.S.A.) 12 13
DOE National Laboratories 1 3
Other 7 8
Data derived from experience to May 1983 and projection thereafter.
186
Table V-II. Representative beams accelerated by the ANL tandem-linacduring the period 1 April 1982-31 March 1983. The quantities q1 and q2 are'the ion charge states after the terminal stripper and the post-tandemstripper, respectively.
Particle q1 q2 Tandem Energy Linac Energy(MeV) (MeV)
12C 5 5 51.0 107160 6 8 59.5 171170 6 8 59.5 15219F 7 9 68.0 1962 4 Mg 7 10 68.0 21228Si 8 13 76.5 2653 0 si 7 12 68.0 21432S 9 14 85.0 242
34S 8 13 76.5 2663 5C1 8 13 76.5 1973 7C1 9 14 85.0 268
40Ca 9 14 85.0 2524 8Ti 9 15 85.0 3245 8Ni 10 19 93.5 41060 Ni 10 19 93.5 32764 Ni 10 19 93.5 38982Se 11 20 102.0 308
2. Status of the Superconducting Linac
The last two resonators of the prototype superconducting linacwere installed and put into operation in October 1982, thus completing the24-resonator system. When these resonators are operated at their maximumlevels, the accelerating power of the combined tandem-linac system isroughly equivalent to that of a 24-MV tandem with two strippers forprojectiles in the range 25 < A < 70.
187
3. Linac Improvements
(J. Aron, R. Benaroya, J. Bogaty, L.M. Bollinger, B. E. Clifft,K. W. Johnson, P. Markovich, J. M. Nixon, R. C. Pardo, and K. W. Shepard)
The pace of development of the prototype linac continues to slow
down as the various problems are solved and the emphasis is shifted to the
ATLAS project. Nevertheless, significant improvements continue to be made.
a. Resonators
The final two resonators of the booster were completed and
installed in the linac in October 1982.
b. Slow-Tuner Pressure Control
A slow-tuner pressure controller that satisfies all requirements
has been developed and installed on all resonators. The excellent
performance of this new system has eliminated one of the main operational
problems of the linac.
c. Liquid-Nitrogen Distribution
A new liquid-nitrogen distribution system with vacuum-insulated
lines and other refinements was installed in March 1982. Since then, there
have been no failures of the LN system, which had previously been a
frequent source of trouble and lost running time on the linac.
d. Helium Compressor
The third compressor for the model 2800 helium refrigerator has
been installed. This compressor will be needed to cool the ATLAS linac.
e. Energy-Measurement System
The beam-energy measurement system that makes use of two beam-
excited resonators has been considerably refined during the past year and
is now used frequently to monitor the beam energy. Numerous electronic
problems have been eliminated and the system can routinely and non-
destructively measure the energy with an accuracy of a few parts in 10.
The new system is now expected to be the primary source of information
about beam energy for most experiments.
188
4. Upgrading of the Tandem
(P. K. Den Hartog, C. E. Heath, and F. H. Munson)
A large number of tasks are carried out annually with theobjective of improving the performance and especially the reliability ofthe tandem. Many of these are difficult and time consuming but of littlegeneral interest. In this section, we mention only those that have themost important impact on the operation of the accelerator.
a. Computer Control and Monitoring of the Tandem
A program to monitor and eventually control the tandem with a
computer has been started. This work is likely to extend over a period of
years because of a shortage of funds and especially personnel to implement
the plans. At the present time, the emphasis is on monitoring all
important parameters of the machine. This work has already progressed far
enough to be very useful for day-to-day operation. An example of this is
the metering and recording of the tandem corona currents. Systematic
information of this kind is expected to point to incipient mechanical
and/or electrical problems.
All major subsystems of the accelerator will gradually be brought
under computer control as time and funds permit. During the past year, a
serial link between the terminal communication system and the computer-
based tandem-monitoring system was put into operation. Also, the foil
chamber in the terminal in now computer controlled.
b. West Injector
The control system for the new injector described in section
I.E.c. has been designed and some components have been acquired. The
control system will be installed in late FY 1983, after all exploratory
tests of the injector have been completed.
c. Control of Tandem-Terminal Voltage
Now that we are routinely accelerating beams with rather complex
mass spectra, the beam analyzer may lock on the wrong ion species when the
accelerator system is recovering from a tandem spark. This problem has
been largely eliminated by requiring the terminal voltage to return to its
original value before voltage control is returned to the beam analyzer.
189
d. Focusing Lens in Terminal
Because of multiple scattering in the terminal stripping foil,
the heaviest ions accelerated by the tandem have a relatively poor
transmission. As part of the ATLAS project, an electrostatic quadrupole
triplet is being installed in the terminal to refocus the beam and hence
improve the transmission of the ion species of interest. This lens and its
control system are now in place and the system is ready for testing.
e. Foil Stripping
The effort to improve the lifetime and quality of stripping foils
is continuing. The primary effort at this time is to try to duplicate the
results of the Japan Atomic Energy Institute, where a new fabrication
procedure was reported to yield exceptionally long lifetimes. This work is
being carried out in collaboration with S. Takeuchi, an exchange visitor
from JAERI.
5. Ion-Source Development
(P. J. Billquist and J. L. Yntema)
This activity is aimed at developing improved negative-ionsources and specialized beams for use in the nuclear-physics program basedon the superconducting linac.
a. Ion-Source Test Facility
The new test facility which was just coming into initial
operation last year has been completed and extensively used to study
several kinds of sources. An emittance-measurement device has been added
to the system and is now in routine operation. The data provided by this
device is essential for a complete evaluation of a source, since it
indicates whether or not the output of the source can be efficiently
transmitted through the tandem.
190
b. Inverted Sputter Source
The inverted sputter source with a new design, first described
last year, has by now been extensively studied and used on-line to provide
beams for the linac. Because of its high intensity, the source is able to
produce acceptable beams of low-abundance isotopes from sputter targets of
a number of natural elements. For example, in a recent nuclear-physics
experiment the unusual beam 5 0Ti was produced from natural titanium.
Experiments aimed at further enhancing the negative-ion yield of
the inverted sputter source are in progress, and preliminary data suggest
that substantial improvements may be feasible. Such an improvement would
be important to our experimental programs, since many beams of interest are
still too weak to be usable.
c. West Injector for the Tandem
A second ion-source position and injector for the tandem has been
designed, installed, and tested. The system performs well and is used
occasionally with the new source described in I.E.b. to provide special
beams for the experimental programs. The remaining task is to install the
electronics system required to control the ion source and injector in
routine operation.
d. The SNICS Source
The SNICS source (the U. of Wisconsin design) has recently been
modified to have internal optics that is similar to that in the ANL version
of the inversted sputter source (described in section I.E.b.). Preliminary
tests of the modified source suggest that it will have a somewhat greater
heavy-ion yield than the inverted sputter source for some ions. If so, it
will be very useful for some beams that are now too weak for the intended
application.
191
e. Hydrogen Loading
For some ion-source target materials such as titanium, calcium,
and zirconium, the negative-ion yield can be enhanced by loading the target
with hydrogen. A loading chamber for this purpose has been built and put
into service. A series of tests have been carried out to learn how to load
targets reproducibly.
6. Near-Term Plans
a. Accelerator Operation
The level of funding in the President's Budget for FY 1984 will
allow the operation of the tandem-linac system to return to a six-day-per-
week schedule and it will also remove the need to shut down the operation
for long periods of time in order to reduce costs. This longer and more
regular schedule of operation will greatly increase running time.
Because of accelerator-improvement activities and the building
activities connected with the ATLAS project, there will continue to be some
interruptions in the accelerator operating schedule. However, these
interruptions will be unimportant until late 1984.
Outside users are expected to play an increasingly prominent part
in the research program at the superconducting linac. Consequently, we
plan to install a formal program of outside-user assistance, as is
discussed in Sec. V.7.
b. Linac Improvements
Most of the activities associated with the linac proper are now
more in the nature of maintenance than improvements. However, upgrading of
both the input and the output beam lines will continue to require effort.
In particular, we need to tackle the general problem of computer control of
beam lines, both because this capability is needed now and because
experience now will be valuable for ATLAS.
192
c. Tandem Improvements
The main tasks through 1984 will be the following: (1) continue
computer monitoring and control of the accelerator, (2) complete the West
Injector, and (3) debug and refine the terminal lens. Completion of these
three projects will enhance operational efficiency and accelerator
capability to an important extent.
d. Ion Sources
There are two main elements to the near-terms plans for ion-
source development. One is the refinement of the inverted sputter source
and the SNICS (Wisconsin) source with the aim of improving efficiency and
ease of operation. Both sources, in their present form, have good basic
characteristics and are used to advantage to provide beams of interest to
the experimental program. However, both also have operational defects that
appear to have straightforward solutions. We will attempt to eliminate
these defects during the next year.
The second task will be to design a new East Injector for use in
ATLAS. One of the main objectives of the design will be to achieve better
mass resolution than is provided by either of the present injectors.
7. Assistance to Outside Users of the Superconducting Linac
The tandem-linac accelerator and its associated experimental
apparatus form a complex system that requires users to master a mass of
technical matters. Consequently, outside users need guidance and
assistance in order to work effectively. Until now, this assistance has
been informal. We propose to start a formal assistance program in FY 1984
by providing a wider range of assistance by a designated group of
individuals with continuing responsibilities.
Outside use of the superconducting linac has continued to
increase, both with respect to the number of persons involved and the total
amount of running time provided. In particular, the fraction of running
time allocated to outside users has increased from 3i% in FY 1982 to 51% in
FY 1983.
193
The severely restricted funding level for FY 1983 in the heavy-
ion program requires that the total running time for FY 1983 be reduced
substantially below the FY 1982 level. This reduction, combined with the
increase in the number of outside users, is making it difficult to
accommodate all users under the present time-allocation policy, in which
all users are allocated time on a uniform basis. Consequently, we now
believe that the time has come to modify the policy, and this issue will be
presented for discussion at the next (second) meeting of the Policy
Advisory Committee. The first meeting of this committee was held in June
1982, at which time the committee recommended that our present informal
system of running-time allocation should be maintained as long as it
continued to work well.
The increased support for heavy-ion research in the President's
Budget for FY 1984 will permit the superconducting linac to be operated
much more intensively than in FY 1983, resulting in a substantial increase
in the availability of running time for outside users. Moreover, the
increasing degree of completeness of the experimental apparatus and
continuing refinements of the accelerator will make the facility a very
attractive one for research in precision heavy-ion research. Consequently,
by FY 1984, outside use of the superconducting linac will be a major
component in the national program for heavy-ion research, and this level of
effort requires that we start to implement a formal user-assistance
program.
Our present plan is to provide the following assistance for
outside users: (1) general liaison services, (2) instruction on the
characteristics of the accelerator system as a whole, (3) help in planning
experiments, particularly with regard to compatibility between the user's
equipment and the accelerator facility, (4) instructions on the use of
particular major apparatus that is part of the ATLAS facility, (5)
instruction and help with the use of computer hardware and software, (6) a
well-defined mechanism for making use of ANL facilities to solve unforeseen
technical problems, (7) some technical support in setting up experiments,
(8) office space, and (9) a minimal level of typing service.
The magnitude of the outside use of the accelerator during the
past year may be judged from the following two lists: (1) the experiments
194
performed by outside users and (2) the institutions represented. As may be
seen from the names associated with each experiment, the university groups
are by now playing a major role in an important fraction of the experiments
and a dominant role in some.
a. Experiments Involving Outside Users
All experiments in which outside users participated during the
period April 1982 to January 1983 are listed below. The names in
parentheses are Argonne collaborators.
(1) Development of a Laser-Spectroscopy Experimental ProgramM. A. Finn, G. W. Creenlees, and S. L. Kaufman, Univ. of Minnesota;R. M. Evans and D. A. Lewis, Iowa State Univ. (C. Davids)
(2) Spectroscopy of100CdL. Cleemann, C. Maguire, W. C. Ma, D. Cacic, and M. Barclay,Vanderbilt Univ. (T. L. Khoo, R. Janssens, D. Frekers, and P.Chowdhury)
(3) Measurement of K-Vacancy Equilibration Lengths in SolidsP. Cooney, Millersville State College (E. Kanter, D. Schneider, andB. Zabransky)
(4) Measurements of Nuclear States of 15 2YbY.-H. Chung, P. J. Daly, Z. Grabowski, J. McNeill, and M. 0.Kortelahti, Purdue Univ. (R. Janssens, P. Chowdhury, and T. L. Khoo)
(5) Tim-of-Flight Measurements of Evaporation Residues Produced in the 160+ Mg Reaction
J. J. Kolata, J. D. Hinnefeld, R. J. Thornburg, and R. J. Vojtech,Univ. of Notre Dame; F. W. Prosser, Jr., University of Kansas (D.Kovar, T. Humanic, R. R. Betts, P. Chowdhury, D. J. Henderson, R.Janssens, W. Kuhn, G. Rosner and K. Wolf)
(6) Accelerator Mass Spectroscopy of 44 TiB. Stievano, INFN, Legnaro (D. Frekers, W. Henning, W. Kutschera, K.E. Rehm, R. Smither, and J. Yntema).
(7) 3 7C1 Induced FusionF. W. Prosser, Jr., Univ. of Kansas (W. Freeman, W. Henning, D.Frekers, D. Geesaman, J. P. Schiffer, and B. Zeidman)
(8) Direct Reactions on 208PbM. Paul, Hebrew Univ., Jerusalem (K. E. Rehm, and W. Kutschera)
(9) Detection of High-Rydberg AtomsZ. Vager, Weizmann Institute (D. Gemmell, E. Kanter, and D.Schneider).
195
(10) Accelerator Mass Spectroscopy of 41CaM. Paul, Hebrew Univ.; X. Ma, Institute of Atomic Energy, Peking (W.Kutschera, D. Frekers, K. E. Rehm, R. Smither, and J. Yntema)
(11) Investigation of 186Hg Isotaeric StateP. J. Daly, Z. Grabowski, Y.-H. Chung, J. McNeill, M. 0. Kortelahti,Purdue Univ. (R. Janssens, D. Frekers, P. Chowdhury, and T. L. Khoo)
(12) Shape Change in 155ErG. Bastin, C. Schuck, CNRS, Orsay; F. Beck, CNRS, Strasbourg; M. 0.Kortelahti, Purdue Univ. (R. Janssens, T. L. Khoo, W. Kuhn, and D.Frekers)
(13) Lifetime Measurements on the 15 8Er* SystemH. Emling, GSI, Darmstadt; R. J. Broda, Y-H Chung, P. J. Daly, Z. W.Grabowski, M. 0. Kortelahti, J. McNeill, Purdue Univ. (P. Chowdhury,W. Kuhn, T. L. Khoo, R. Janssens, and G. Rosner)
(14) Inelastic and Single-Nucleon Transfer for 160 on 40CaJ. J. Kolata, R. J. Vojtech, Univ. of Notre Dame (D. Kovar, R. Pardo,K. E. Rehm, G. Rosner, and H. Ikezoe)
(15) Tusion with 40Ca BeamsH. A. Al-Juwair, R. J. Ledoux, M.I.T. (R. R. Betts, and S. Saini)
(16) Fission and Fast Fission for the Systems 19F, 2 4Mg, 28Si and 208PbC.-K. Gelbke, B. Tsang, W. G. Lynch, H. Utsunomiya, Michigan StateUniv.; P. A. Batsden, M. A. McMahan, Lawrence Livermore Laboratory(B. Back and S. Saini)
(17) Very High Spin States in 147GdJ. Borggreen, G. Sletten, Niels Bohr Institute; R. J. Broda, Y.-H.Chung, P. J. Daly, Z. W. Grabowski, M. 0. Kortelahti, and J. McNeill,Purdue Univ. (P. Chowdhury, R. Janssens, T. L. Khoo, D. Frekers, andW. Kuhn)
(18) Isomers in N = 82 NucleiR. J. Broda, Y-H Chung, P. J. Daly, Z. W, Grabowski, M. 0.Kortelahti, and J. McNeill, Purdue Univ. (T. L. Khoo, R. Janssens,and P. Chowdhury)
(19) Two Electron Titanium WavelengthsA. E. Livingston, Univ. of Notre Dame (H. G. Berry, J. Hardis, and W.Ray)
(20) Structure of Hg IsotopesR. J. Broda, Y-H Chung, P. J. Daly, M. 0. Kortelahti, Z. Grabowski,and J. McNeill; (R. Janssens, T. L. Khoo, and D. Frekers)
196
b. Outside Users and Institutional Affiliations
(1) Michigan State UniversityD. A. ArdouinC.-K. GelbkeW. G. LynchB. TsangH. UtsunomiyaZ. Xu
(2) Purdue UniversityR. J. BrodaY.-H. ChungP. J. DalyZ. W. GrabowskiM. O, KortelahtiJ. McNeill
(3) Notre Dame UniversityJ. D. HinnefeldJ. J. KolataA. E. LivingstonR. J. ThornburgR. J. Vojtech
(4) Vanderbilt UniversityM. BarclayD. CacicL. CleemannW. C. MaC. Maguire
(5) Iowa State UniversityR. M. EvansD. A. Lewis
(6) University of KansasF. W. Prosser, Jr.
(7) Lawrence Livermore LaboratoryP. A. BaisdenM. A. McMahan
(8) M.I.T.H. A. Al-JuwairR. J. Ledoux
(9) University of MinnesotaM. A. FinnG. W. GreenleesS. L. Kaufman
(10) Millersville State CollegeP. Cooney
197
(11) U. S. Naval AcademyT. Humanic
(12) CNRS, OrsayG. A. BastinC. Schuck
(13) CNRS, StrasbourgF. Beck
(14) University of CopenhagenJ. BorggreenG. Sletten
S. Bjdrnholm
(15) G.S.I., DarmstadtH. Emling
(16) Hebrew University, JerusalemM. Paul
(17) INFN, Legnaro (Italy)B. Stievano
(18) Weizmann Institute
Z. Vager
(19) Institute of Atomic Energy, Peking, P.R.C.X. Ma
c. Summaries of Major User Programs
Several groups listed in the above tables have embarked on
extensive research programs that are likely to make use of the tandem-linac
accelerator for several years. In order to give some indication of the
extent of these efforts, the following descriptions summarize the research
of five groups that have been most active during the period April 1982 to
March 1983.
i. The Purdue University Group (P. J. Daly, Z. Grabowski, Y. H. Chung,
S. R. Faber, H. Helppi, M. Kortelahti, A. Pakkanen, J. McNeill,
and J. Wilson)
The Purdue University group has an active program on high-spin
nuclear states at the linac. The personnel currently includes two
professors, one visiting scientist from Poland, one post-doc, and three
graduate students. One student whose thesis was largely based on work
198
conducted at the linac has already graduated. A second student, whose work
was entirely based on linac experiments, will soon complete his thesis.
Our program uses in-beam Y-ray techniques and is directed at
several aspects of nuclear structure at high spin. We are testing the
validity at the Z = 64 sub-shell closure through spectroscopic studies of N
= 82 nuclei close to the proton drip line. This past year a 40-us 10+
isomer was discovered in t7Yb82 which, having a half-filled proton h1 1 /2
shell, was predicted to have a long-lived isomer. By studies on N = 87 and
88 Dy isotopes we are also investigating the transition between oblate
aligned-particle and prolate-collective structures as a function of both
spin and neutron number. Evidence for a prolate-to-oblate shape change has
been found in 153,154Dy. Studies in 186Hg have revealed for the first time
decoupled vi1 3/ 2 bands with both prolate and oblate shapes.
The program is conducted in close collaboration with the Y-ray
group at Argonne and details may be found elsewhere in this document.
We have begun a project to construct a superconducting solenoid
lens to be used as a conversion-electron spectrometer. The solenoid has
been delivered by the manufacturer and the magnetic field profile has been
determined to be within specifications. The spectrometer is currently
being assembled at Purdue and, after testing there, will be installed at
Argonne late in 1983. A lens spectrometer, on loan from the University of
North Carolina and Oak Ridge National Laboratory, has been prepared for on-
line use in the interim period.
ii. University of Kansas Collaboration (F. W. Prosser, Jr.)
Heavy-ion reaction mechanisms are being studied by observing the
partition of reaction cross section and its dependence on energy and
neutron excess. Fusion-fission,. fusion-evaporation, and deep inelastic
scattering for 32S projectiles incident on targets of 112,116,120,124Sn
were studied over the energy range 130-247 MeV. In a search for entrance-
channel effects in the formation of compound systems, the even-A Sn
isotopes 112-1 1 4 Sn were bombarded with beams of 58Ni and 64Ni at laboratory
energies that varied from 230 to 322 MeV. In these measurements, the
influence of neutron excess (for both target and projectile) upon the
fusion-evaporation yields was emphasized.
199
In addition, the energy dependence of fusion and incomplete
fusion processes for lighter systems involving 28Si have been studied. In
a search for incomplete momentum transfer (i.e., incomplete fusion),
velocity spectra were measured for individually-resolved evaporation-
residue masses produced in reactions of 28Si projectiles at Elab >, 260 MeV
on targets of 12 C, 24Mg, 2 4Al, 28Si, and 4 0 Ca. Also, in order to
investigate the role of entrance-chanrel effects, evaporation-residue cross
sections were measured for the reactions 28Si + 28Si and 160 + 40Ca, which
form the same compound nucleus 5 6Ni. The 2 8Si + 28Si system displays
significantly smaller cross sections at higher energies than does 160
+ 40Ca. Further investigations of this effect are planned.
iii. MSU and LLL Collaboration (C. K. Gelbke, W. Lynch, M. S. Tsang,
Z-Xu, P. Baisden and M. McMahan)
The properties of fission fragments from the 32S + 20 8Pb reaction
have been studied in detail. These studies include measurements of cross
sections, angular distributions, fragment masses, and folding-angle
distributions at projectile energies of 180-270 MeV. This study shows that
compound-nucleus formation is strongly suppressed for this reaction system
even at the lowest bombarding energies, with a major fraction of the cross
section going to the quasi-fission reaction. In a subsequent experiment,
which is presently being analyzed, we have measured angular distributions
for 19F, 24Mg, 2 8Si + 20 8Pb reactions over a range of beam energies in an
attempt to localize the onset of quasifission, which is known to be absent
in the 160 + 2 08Pb reaction and dominating in the 32S + 2 08Pb reaction.
In the next experiment we plan to measure the neutron emission
from the 32S and 2 0 8 Pb reaction with the aim of determining the ratio of
pre- to post-fission neutrons. It is anticipated that such measurements
will be helpful in determining the time scale of the quasifission reaction,
a quantity which is of central importance for the development of a better
understanding of heavy-ion reaction dynamics involving large mass
transfers.
200
iv. Iowa State and Minnesota Collaboration (D. A. Lewis, R. M. Evans,
G. W. Greenlees, and S. L. Kaufman and M. A. Finn)
This project will 'se on-line laser spectroscopy to study the
optical hyperfine structure of radioactive atoms. The objective is to
extract information on spins, moments, and the variation of charge radii
for ground states and isomers. The species under investigation will be
produced by heavy-ion beams fromthe tandem-linac. The radioactive atoms
recoil from the production target, become thermalized in a helium
atmosphere, and then are transported by a liquid-nitrogen-cooled helium jet
to the laser interaction region. Resonance fluorescence spectroscopy will
be employed to observe the optical transitions. Essentially Doppler-free
linewidths will be obtained by collimating the atoms into an atomic beam as
they emerge from the helium jet. Two cooled photomultiplier tubes will
detect the fluorescent light.
The linac target station for the cryogenic helium jet has been
completed. Tests using the linac beam have been conducted, indicating
copious production of the Ba radionuclides using the 12 2Sn(1 2C,xn)1 3 4-xBa
reactions. The skimmer efficiency for Ba is 2.5%, slightly higher than
that obtained for lighter As, Ge, and Ga isotopes. A large blower pump has
been installed, which should lead to better cooling of the atomic beam upon
emergency from the capillary. The laser beam transport system between the
laser laboratory and the cryogenic helium jet has been installed. Tests to
reduce the background of scattered laser light will begin soon. It is
probable that measurements with a complete system will begin in the summer
of 1983.
v. University of Notre Dame (J. Kolata, J. Hinnefeld and R. Vojtech)
We have participated in studies of the energy dependence of
fusion and incomplete fusion cross sections for reactions induced by 160
and 2 8Si projectiles. Velocity spectra of individually-resolved
evaporation-residue masses produced in 160 + 12C, 2 4 Mg, and 40Ca reactions
at Elab(1 60) < 150 MeV and 2 8Si + 12C, 2 4Mg, 2 7A1, 2 8Si, and 40Ca reactions
at Elab(2 8Si) < 260 MeV were measured by means of time-of-flight
techniques, and the results were compared with theoretical predictions for
201l
complete fusion. Evidence for incomplete momentum transfer (i.e.,
contributions from incomplete fusion) was observed at the higher bombarding
energies for some systems, but not for others. Further investigations of
this projectile-target dependence are planned. As a part of a study of the
energy dependence of reactions induced by a variety of projectiles on 40Ca
and 2 0 8 Pb, the cross sections for elastic and inelastic scattering and for
transfer reactions were measured for the 160 + 4 0Ca system at Elab( 1 6 0)
150 MeV. The angular distributions will be compared to the predictions of
DWBA and CCBA to test the adequacy of the calculations at the higher
bombarding energies.
203
B. OPERATION OF THE DYNAMITRON FACILITY
The Physics Division operates a high-current 4.5-MV Dynamitron
accelerator which has unique capability as a source of ionized beams of
most atoms and many molecules. Among the unusual facilities associated
with the Dynamitron are (1) a beam line capable of providing
"supercollimated" ion beams permitting angular measurements to accuracies
of 0.005 degree, (2) a beam-foil measurement system capable of measuring
lifetimes down to a few tenths of a nanosecond, (3) an experimental system
dedicated to measuring absolute nuclear cross sections at low energy, (4) a
variety of experimental apparatus for weak-interaction studies, (5) a
simultaneous irradiation system by which heavy ions from the Dynamitron and
helium ions from a 2-MV Van de Graaff accelerator are focussed on the same
target, (6) a post-acceleration chopper system giving beam pulses of
variable width from about one nanosecond to the millisecond range at
repetition rates variable up to 8 MHz, (7) a scattering chamber for
electron spectroscopy with electrostatic parallel-plate electron
spectrometers with variable energy resolution (0.1% to a 5%) and the
capability to measure electron energies up to a few keV as a function of
observation angle, and (8) a McPherson electrostatic spherical electron-
spectrometer system capable of measuring electron energies with high
precision and very high efficiency. A PDP-ll/45 computer system is used
for on-line data analysis and for the control of experiments.
1. OPERATIONAL EXPERIENCE
B. J. Zabransay, D. Schneider, R. L. Amrein, and A. E. Ruthenberg
Overall, the Dynamitron continued to perform well during the past
year. The normal operating schedule was twenty-four hours a day, five days
a week. Very little running was done on weekends during calendar year
1982.
During the year the accelerator was staffed a total of 5380
hours. Of this time 4729 hours (88%) were scheduled for experimental
research during which a beam was provided to the experimenters 90% of the
time. Machine preparation time used up 6% of the scheduled research time
204
and machine malfunctions 4%. Scheduled accelerator improvements (including
the upgrading program) and modifications used a total of 651 hours or 12%
of the total available time.
The great versatility of the Dynamitron continued to be exploited
by the research staff. Ion currents on target varied from less than a
nanoampere to about 100 microamperes with ion energies ranging from 0.2 to
4.0 MeV. A wide range of both atomic and molecular ions was delivered on
target. They included 1H+, 1H + 2H+ 1H + 3 He+, 2H2+ 4He+ 4HeH+ 2H3+,
7L + 7L +, 7Li , 12C+ 14N 4 1N++, 28e+ 20Ne++, 4 N +40Ar+Ni N LiNe,2'40Ar++ 40Ar+++
During the year a total of 55 investigators used the Dynamitron
in some phase of their experimental research. Of these, 12 were from the
Physics Division, 10 were from other Argonne research divisions, 21 were
outside users from other research facilities, 9 were members of the
Resident Graduate Student Program, and 3 were undergraduate students
participating in research at the Dynamitron. Of the scheduled time, 89%
went to experiments involving members of the Physics Division, 10% to other
Argonne divisions, and 1% was exclusively assigned to outside users.
However, outside users collaborated in experiments that used 66% of the
total available time. Undergraduate students and participants in the
Resident Graduate Student Program worked on experiments that used 77% of
the time.
The accelerator has been heavily used by several research groups
during 1982. It has been operating with only routine maintenance problems
and relatively free of sparking for voltages up to 4 MV. Sparking above 4
MV is still a problem. The terminal control rods continue to be damaged
even with special modifications. Early in 1983 the accelerator tube will
be reoriented to try to correct this problem. A system to eliminate the
control rods by the use of fiber-optic or infrared light-link control of
stepping motors is being studied. Step-by-step improvements to the various
machine components and configurations will be made as tests of the maximum
energy-holding capability continue.
The fiber-optic light-link system for monitoring electrical
parameters within the high-voltage terminal was damaged again by a series
of sparks when the machine was operating in the 4-MV range. The fiber-
optic bundle was removed to allow operation at higher energies. It will
again be installed after being repaired and after the accelerator tube is
reoriented. The bundle will be repositioned on the column so as to reduce
damage.
205
Two beam lines were changed this year. One was built up to allow
experiments using a McPherson electron spectrometer. A scattering chamber
for electron spectroscopy was added to another beam line. The experimental
area was improved with a large increase in the ambient light and a general
organization of the area. Various vacuum improvements were made to several
of the beam lines.
The development of ion sources to provide ion species of interest
to specific experimental groups has proceeded slowly during the year
because of the decrease in the number of technical staff. A beam of Li+
can now be produced easilyand was used many times during the year. With
only a minor modification, it is hoped that a Be+ beam can be produced from
the same source. A Penning source is being modified to accept cathodes
made of Si in order to produce a Si+ beam. The machining of the Si uses a
special process and is being done by the Dynamitron technical staff.
A Capillaritron ion source is under development. It uses a
nozzle with a 25-micron orifice. When gas flows through the nozzle and it
is biased at 2 to 15 kV, a plasma forms just inside the tip, producing
copious quantities of various ions. Initial tests are encouraging but many
problems, including poor focussing and a high gas load on the accelerator
tube, will have to be overcome.
2. UNIVERSITY USE OF THE DYNAMITRON
B. J. Zabransky
The Argonne Dynamitron continues to be a valuable research
facility for scientists from outside institutions. It is not only the
accelerator itself that attracts outside investigators but also the unique
associated experimental equipment as well as the on-going research program
being conducted at the Dynamitron.
Most visiting scientists chose to collaborate with local
investigators on problems of common interest. A few, however, worked as an
independent group. Some came for a one-time-only experiment, but most are
participants in research programs that have spanned a period of several
years.
During the year twenty-one scientists came from thirteen outside
institutions to use the Dynamitron. They came from eight states and three
foreign countries. They participated in experiments that used 66% of the
time scheduled for research. A list of those institutions from which users
of the Dynamitron came during 1982 is given below. The list includes the
206
name of the institution, the title of the research project, and the names
of the principal investigators. The names of their Argonne collaborators
are enclosed in parentheses.
(1) Arizona State UniversityDevelopment of Capillaritron Ion Source
J. Kelly, (D. S. Gemmell)
(2) University of Freiburg, Berlin, West GermanyElectron Spectroscopy of Fast-Ion CollisionsUsing Simultaneous Laser Excitation
R. Bruch, (D. Schneider, W. St6ffler, V. Pfeufer,B. Zabransky, H. G. Berry, and P. Arcuni)
(3) Fudan University, Shanghai, ChinaInfluence of Rydberg States in Convoy Electron Measurements
Gu Yuan Zhuang, (D. S. 2emmell, E. P. Kanter,D. Schneider, Z. Vager, and B. J. Zabransky)
(4) Marquette UniversityRadiation Damage of Covalent Crystal Structures
L. Cartz, A. Gowda, F. G. Karioris,and T. Ehlert
(5) Northwestern UniversityDirect Capture in the 2 7 Al(p,Y) and
R. E. Segel, E. Zupranska,* G.(A. J. Elwyn, and W. Ray)
1 9 F(p,Y) ReactionsHardie,* M. Wiescher,*
(6) University of Notre DameSpectra of High Spin States in Light Elements
A. E. Livington, (H. G. Berry, J. Hardis, and W. Ray)
(7) Ohio State UniversityDirect Capture in the 2 7 A&(p,Y) and
M. Wiescher, G. Hardie,* R. E.(A. J. Elwyn, and W. Ray)
1 9 F(p, Y) Reactions
Segel,* E. Zupranska,*
(8) University of TexasAutoionization Electron Spectroscopy of Li, He, Ne, and Ar
C. F. Moore, P. Seidel, (D. Schneider, P. Arcuniand W. Stoffler)
(9) University of ToledoMeasurements of Forbidden Transition Rates
P. S. Ramanujam, L. Curtis, (H. G. Berry,J. Hardis, and W. Ray)
(10) Valp raiso UgiversityThe Li(d,p) Li Reaction and Solar Neutrino Capture Rates
D. Koetke, (B. Filippone, A. J. Elwyn, and W. Ray)
*From another outside institution.
207
(11) Weizmann Institute, Rehovot, Israel
Studies of Beam-Foil Excited Rydberg AtomsZ. Vager, (D. S. Gemmell, E. P. Kanter, D. Schneider,and B. J. Zabransky)
(12) Western Michigan Univerity 19Direct Capture in the AI(p,Y) and F(p,Y) Reactions
G. Hardie, R. E. Segel,* M. Wiescher,* E. Zupranska,*A. J. Elwyn, and W. Ray)
(13) Yale UniversityMicrowave Field Ionization of Foil-ExcitedFast Rydberg Atoms
P. Koch, D. Mariani, W. van de Water, (D. S. Gemmell,E. P. Kanter, D. Schneider, and B. J. Zabransky)
The Resident Graduate Student Program is open to students that havefinished their course work and passed their prelims. They come to Argonneand perform their Ph.D. thesis research here. Nine members of this programworked at the Dynamitron during 1982. Altogether they participated inexperiments that used 77% of the time allotted to research. Those who usedthe accelerator are listed below, together with their home university andtheir local thesis advisor.
(1) P. W. Arcuni, University of ChicagoH. G. Berry, advisor
(2) R. Evans, Iowa State UniversityC. N. Davids, advisor
(3) B. Filippone, University of ChicagoC. N. Davids, advisor
(4) M. Finn, University of MinnesotaC. N. Davids, advisor
(5) C. A. Gagliardi, Princeton UniversityG. T. Garvey, advisor
(6) J. Hardis, University of ChicagoH. G. Berry, advisor
(7) A. R. Heath, University of ChicagoG. T. Garvey, advisor
(8) W. Stbffler, Free University of BerlinD. Schneider, advisor
(9) G. Zapalac, University of ChicagoH. G. Berry, advisor
*From another outside institution.
208
In addition, the following undergraduate students have participated inresearch based at th Dv'iamitron.
(1) J. Bales, North Carolina State UniversityD. S. Gemmell, advisor
(2) J. J. Hofmann, East Stroudsburg State CollegeD. Schneider, advisor
(3) J. E. Tkaczyk, Rutgers UniversityE. P. Kanter, advisor
2091,1
VI. DATA ACQUISITION AND ANALYSIS SYSTEMS
A. ON-LINE
The construction of a new accelerator (ATLAS) has provided the
opportunity to examine critically the future needs of the Division with
respect to data acquisition and has led to the conclusion that the present
system based on PDP 11/45's with the operating system DOS could not fulfill
the anticipated needs. Hence, for the moment, the present on-line data-
acquisition systems are being only maintained and no extensive development
effort is planned for them.
B. OFF-LINE
The VAX 11/780 is proving to be very useful for analysis and is
being used for an ever-increasing variety of purposes. To enhance its
capability a 6250 bpi, 125 ips magnetic tape unit was ordered (and as of this
writing, installed); an additional 1.5 Mb of memory was likewise installed
thus bringing the total memory to 5 Mb; and lastly, a floating-point
accelerator has been ordered and received but not yet installed.
C. FUTURE
A project has been initialized to provide for the data-acquisition
systems needs for the future. The project (called DAPHNE, for Data-
Acquisition by Parallel Histogramming and NEtworking) involves parallel
processors to histogram buffers of events before passing them to the main
acquisition computer. The project is now into its planning phase and
feasibility studies are being performed.
2111/1.
AEOMIC AND MOLECULAR PHYSICS RESEARCH
Introduction
The Atomic Physics research in the Physics Division currently consists ofthe following six ongoing- programs:
(1) Photoionization-photoelectron research (J. Berkowitz),
(2) High-resolution laser-rf spectroscopy with atomic and molecular beams(W. J. Childs and L. S. Goodman),
(3) Beam-foil research and collision dynamics of heavy ions (H. G.Berry),
(4) Interactions of fast atomic and molecular ions with solid and gaseous
targets (D. 3. Gemmell and E. P. Kanter),
(5) Theoretical atomic physics (K. T. Cheng),
(6) Electron spectroscopy with fast atomic and molecular-ion beams
(D. Schneider).
Major new opportunities that we see for our work in the near future lie inextension of the rf-laser double resonance work to atomic and molecularions, the use of VUV lasers in studies on the photodissociation ofmolecular ions, and at the Dynamitron, further studies with fast molecular-ion beams and the spectroscopy of few-electron heavy-ion systems.
During FY 1981 and FY 1982 we have been fortunate in having, as a visitingscientist from the Hahn-Meitner Institute (Berlin), Dr. Dieter Schneider, aphysicist who has specialized for several years in accelerator-based atomicphysics and in electron spectroscopy in particular. Beginning February 1,1982, Dr. Schneider joined the permanent staff of the Physics Division.Beginning in FY 1983, Dr. Schneider became the Principal Investigator in anew program of electron spectroscopy based at the Dynamitron. His programintegrates into and complements nicely the other existing programs inAtomic Physics in the Physics Division. Together, the three programs inphysics with fast molecular ions, beam-foil spectroscopy, and electronspectroscopy account for about 75% of the beam time available at theDynamitron.
Already we have seen some fruits from the symbiotic nature of theseprograms. The recent discovery at the Dynamitron of the previouslyunrecognized role of 'ydberg atoms in convoy-electron studies is a goodexample.
During FY 1982, Dr. H. G. Berry was on overseas leave for 9 months. Hespent 6 months at the Laboratoire Aim Cotton, Orsay, France, and 3 monthsat the University of Lund, Sweden.
213
VII. PHOTOIONIZAT ION-PHOTOELECTRON RESEARCH
Introduction
Our photoionization research program is aimed at understanding-the basic processes of interaction of light with molecules, the electronicstructures of molecules and molecular ions, and the reactions of molecularions, both unimolecular and bimolecular. The processes and species westudy are implicated in a wide range of chemical reactions, and are ofspecial importance in outer planetary atmospheres and in interstellarclouds. Our work also provides fruitful tests for theories of electronicstructure, which help in the evaluation of widely applicable models formulti-electron systems. Most of this work is of a fundamental nature, butwe also use the precise methods developed here to determine thermochemicalquantities (heats of formation and ionization potentials) directly relevantin, e.g., reactions with ozone in the stratosphere, possible side reactionsin a magnetohydrodynamic generator and reactions in interstellar clouds.Our experimental studies utilize five pieces of apparatus - twophotoionization mass spectrometers and three photoelectron energy analyzers- each with special features.
(1) A three-meter normal-incidence vacuum-ultravioletmonochromator combined with a quadrupole mass spectrometer. This apparatusis capable of the highest resolution currently achieved in photoionizationstudies. It is also convenient for investigation of wavelength-dependentphotoelectron spectra.
(2) A one-meter normal-incidence VUV monochromator mated with amagnetic-sector mass spectrometer. This apparatus has higher massresolution, is less discriminatory in relative ion-yield measurements, andcan be used to study metastable ions. Higher intensity for weak signalscan also be achieved.
(3) Two cylindrical-mirror photoelectron-energy analyzers, whichaccept a large solid angle of photoelectrons, close to the "magic angle" of54*44'. One has been extensively used for the determination of thephotoelectron spectra of high-temperature species in molecular beams, andthe other has on occasion been mated with the three-meter monochromator forstudies of photoelectron spectra as a function of wavelength.
(4) A hemispherical electron-energy analyzer incorporated in achamber which permits one to rotate the analyzer over a substantialfraction of 4n. This device is intended for angular-distributionmeasurements, and also enables us to study very-high-temperature species.
The experiment involving UV laser photodissociation of molecular
ions has progressed to the point where photofragment signals can be readilydetected, without long searches. In the near future, the magnetic massspectrometer will be dedicated to this work.
One year ago, the interfacing of a multitask minicomputer withour experimental apparatuses was incomplete. Only the photoionization massspectrometric experiment was minicomputer controlled. Now thephotoelectron apparatus and the laser photodissociation experiment are alsocomputer interactive, the latter employing a serial highway and driver.
214
The experiment involving- UV laser photodissociation of molecularions advanced one more stage. A quadrupole mass spectrometer wasincorporated to select the mass of the primary molecular-ion beam. The
problems anticipated with this addition, involving- a quadrupole source andelectronics floating at high voltage, were overcome without greatdifficulty. In the forthcoming year, major challenges are expected when amultichannel array detector is introduced, together with a new laser adRaman shifter.
An important practical achievement was the production of atomicchlorine, and its transportation to the interaction region without rapidrecombination and loss. Similar techniques should enable us to examineother transient species.
Other technical progress included:
(1) The completion of an extensive photoelectron experimental
study on the lanthanide trihalides, using both the He I (584 %) and He II(304 A) incident radiation. The relative binding- energies of 4f-like andligand-like orbitals were clearly revealed in these experiments.
(2) The initiation of photoelectron spectroscopic studies on a
class of Group III metal oxides, including Ga20, In20 and B202 .
(3) The attainment of a photoionization spectrum of atomicchlorine, from ionization threshold at ~ 956 A to ~ 750 A. Autoionizationresonance features converging to P, 1 D2 aad ISo ionic limits were clearlyseen, with good resolution (0.28 0).
(4) UV laser photodissociation studies were made on severalmolecular ions. The experiments measure kinetic energy release in thecenter of mass, both by time-of-flight velocities and by momentumanalysis. Good agreement has now been achieved between these twomethods. These experiments are detailed below.
a. Photoelectron Spectra of the Lanthanide Trihalides and their
Interpretation (B. Rusci6, G. L. Goodman and J. Berkowitz)
The He I photoelectron spectra of gaseous LaCi3 , LaBr3 , LaI3 ,
CeBr3 , CeI3 , NdBr3 , Nd1 3 , Ern3 , LuBr3 and LuI3 have been obtained. They
display apronounced increase in splitting, and hence a progressively
clearer definition of peaks in the valence band as either the halogen or
the lanthanide increases in atomic number. These experimental features,
together with a refined relativistic Xa DVM calculation using the
von Barth-Hedin potential, have enabled us to assign these peaks with
confidence. The He II photoelectron spectra of CeBr3 , NdBr3 and LuI3 were
also obtained. They reveal that the 4f-like ionizations of early
215
9 10 II 12 13IONIZATION ENERGY (eV)
liii III(b) CeBr
"" I'.
D.. -
CD - -
8 9 10 11 12 13IONIZATION ENERGY (eV)
20
1500
V)
z
LU
H? 1000Z0
I-0-JWo 50000
I-
24O
-V00
1111 III
(a) CeBr3
iey0
0 -0
*
0 00 -0
I '1*
9 IC II 12 13IONIZATION ENERGY (eV)
(d) LuI3
" N V ,. _
8 12 14 i16IONIZATION ENERGY (ev)
14 15
Fig.VII-l. The 21.2-eV photoelectron spectrum of an early lanthanide,CeBr in (a) displays the halogen p-like valence band. The 40.8-eVspectrum in (b) reveals an additional peak at lower ionization energy(%9.6 eV), attributable to a 4f-like ionization. The 21.2-eV spectrumof a late lanthanide. LuI3 , is displayed in (c), and shows enhancedsplitting. The 40.8-eV spectrum of LuI3 in (d) has additional peaks dueto 4f-like ionizations, but at much higher energy (4l6.2 and 17.7 eV)than the valence band. Calculated energies are indicated by tick marksat the top of each figure.
n.
(c) LuI 3
0
I *
iOi/
J 0 0- 8
4
H
z
z
z 200
-JW0
OHI
rc
0
Z 6CH
-J00 7
ij hc
216
lanthanide members (e.g. Ce) occur at lower energy than the ligand valence
band, but that those of late members (e.g. Lu) are core-like. The
aforementioned calculations reproduce this behavior quantitatively. They
also help to rationalize a bi-modal behavior in the valence band; the
spectra with the 4f shell less than half-filled are very similar, as are
those with the 4f shellmore than half-filled, but the two groups are
distinctly different. The width of the valence bands, which varies over a
factor 2.5, is correctly reproduced. The calculations have been extended
to include fluorides. Both the calculations and available experimental
comparisons yield a picture in which the lanthanide fluorides display
predominantly ionic bonding (Ln2 .2 +); the bonding takes on successively
more covalent character as one proceeds to chlorides (Ln1.6 +), bromides
(Ln1.3+) and iodides (Lnl.0+). (See Fig. VII-1.)
b. Photoelectron Spectra of Metal Oxide Vapors of Group III(B. Ruscit, G. L. Goodman, and J. Berkowitz)
The metal oxide vapors M2 0 (M = Al, Ga, In, T) have been studied
mass spectrometrically, by electron diffraction and by matrix isolation
infrared spectroscopy. Their structure (bent or linear) is still not
certain. We have obtained He I photoelectron spectra of all the above
species except A1 2 0, and have used Xa DVM calculations to interpret these
spectra. Our results cannot be used to distinguish geometric structures,
but they do shed light on the orbital composition of these species.
In each instance, the band at lowest ionization energy is rather
narrow, and is followed by broader bands. The energy separation between
narrow and broad features decreases as the metal atomic number increases.
This pattern was previous]; observed in the PES of Group III metal
monohalides. The ionic bonding model which was used to interpret those
spectra appears to be applicable here as well. In that model, the narrow
lowest-energy peak was attributed to ionization from a molecular orbital
largely composed of metal s and p orbital. The Xa DVM calculations
support this interpretation for the metal oxides except for T 2 0, where the
calculations indicate that this orbital has acquired a large 0 2p
character. There are additional discrepancies between the experimental PES
217
of T920 and the corresponding- calculations which we are currently trying- to
resolve.
c. Photoelectron Spectrum of B02 (B. Rusci6, L. A. Curtiss,*and J. Berkowitz)
It has been known for some time that the gaseous species B2 02 is
generated when a mixture of boron and B2 03 is heated to ~ 1200 C. We have
examined this species effusing from an oven by VUV photoelectron
spectroscopy, using- the He I resonance line as incident radiation. We have
thus far observed four peaks, with maxima at 13.62, 14.45, 15.33 and 15.85
eV. Hartree-Fock calculations clearly indicate that the most stable
neutral molecular structure is 0-B-B- less 0. The linear structures B-0-B-
0, B-0-0-B and the planar rectangle are stable by 1.8, 9.2 and 12.3 eV,
respectively. Furthermore, the calculated orbital energies of 0-B-B-0 are
the only ones that closely approximate the observed energies.
Vertical ASCF energies calculated with a 4-31 G basis set yield
13.72, 14.63, 16.16 and 16.50 eV for the four lowest energy ionizations,
which correspond to electron ejection from i ,ru, ag. and au orbitals,
respectively.
The structure 0-B-B-0 is isoelectronic with the stable cyanogen
structure NEC-C=N. However, the orbital sequence exhibited in the PES of
C2N2 is clearly different. There, the two sharp peaks characteristic of
ionization from a orbitals occur at energies intermediate between the Wg.
and lru ionizations. In both cases, vibrational excitation is observable in
the bands resulting from it orbital ionizations, which are also the ones
having the largest area. This provides additional confirmation for our
assignments.
*Chemical Engineering'Divisio'.t, ANL.
c. Photoelectron Spectrum of ALF (J. Berkowitz)
In the course of trying- to prepare CaF vapor for photoelectron
spectroscopic study, aluminum metal and CaF2 were combined and heated. For
reasons now well understood, CaF was not generated but instead a highly
218
satisfactory spectrum of the previously unexplored ALF was obtained. Its
spectral pattern fits well with those of other Group III monohalides (TLX,
InX) previously studied in this laboratory.
e. Photoelectron Spectra of BiX3 and BiX (G. Jonkers* and J. Berkowitz)
A combination of single-oven experiments to generate Bi 3 and
BiBr3 vapors, and double-oven experiments in which these vapors were
permitted to react with independently heated bismuth have succeeded in
generating the trihalide and monohalide independently. An unequivocal
interpretation of the results must await the completion of these
experiments.
*Netherlands-U.S. Exchange Fellow, Fulbright Program.
f. Photoionization of Atomic Chlorine (B. Ruscit, J. P. Greene,
and J. Berkowitz)
Chlorine has become a test case for ab initio theories of the
photoionization of open-shell atoms. In order to incorporate
autoionization resonances, a many-body theory (MBT) is required. An
experimental result is essential for testing these theories.
For this experiment, atomic chlorine is generated in a microwave
discharge. Recombination of these atoms is largely prevented by coating
the reactor wall with an appropriate agent. The photoionization experiment
is performed with the use of a three-meter monochromator and quadrupole
mass spectrometer.
The photoionization spectrum displays some resonance features
converging to 3P1, three prominent series (one broad and two narrow)
converging on 1D2 and two series converging on 1S0. Of the two
calculations (R-matrix and diagrammatic MBT) recently published which
attempt to predict the resonant structure, the latter comes much closer to
the experimental observations, both in terms of quantum defects, peak
shapes and absolute intensities. However, a major discrepancy even here is
the appearance of two narrow series converging on 1D2 , where only one is
predicted in the calculation. (See Fig. VII-2.)
219
d' l5d'
7s~8s6d"
ti
1
7s5d 6c 8s
i 7d
9s
' I6
6s
13.5 14.0PI0T0N ENERGY (eV)
h
(a)look-Fig. VII-2. A portion of
the photoionizationspectrum of atomicchlorine obtained in thecurrent experiments isshown in (a); a spectrumof the same regioncalculated by Brown et al.1
using diagrammatic many-body perturbation theory,is shown on a commonenergy scale in (b). Theshapes of the "d" and "s"
series features isreproduced in thecalculation (the "s"members having beentruncated at 60 Mb), butthe "d" series is absentin the calculations.Instead, a dip accompanieseach "s" member.
E. R. Brown, S. L. Carter,and H. P. Kelly, Phys.Rev. A 21, 1237 (1980).
801-
60k-4d155d
40 -
201-
NE0
0
b*1'
iiC I I I
(b)
401-
201-
4d 6s
K)14.5
-
1 L
'I
a
I
T
13.0
220
g. UV-laser Photodissociation of Molecular Ions (R. E. Kutina,A. K. Edwards, and J. Berkowitz)
The study of the interaction of electromagnetic radiation with
molecular ions represents an exciting challenge for the future, both in
terms of spectroscopy and of dynamics. One channel that is convenient for
experimental study occurs when the molecular ion dissociates as a
consequence of the interaction, yielding-a product which is easily
distinguishable from the target. In the present study, the primary ion is
produced by electron impact, mass-selected by a quadrupole mass
spectrometer, and crossed by pulsed exeimer-laser radiation. The fragment
ion is selected by a magnetic mass spectrometer. The precise momentum in
the laboratory frame can be related to kinetic energy release following
photodissocie.tion in the center of mass frame. A time-of-flight velocity
measurement provides equivalent information. An important feature of the
current experiments is the use of a UV laser (hv = 6.4 eV), whic i provides
sufficient energy to dissociate most molecular ions, whereas earlier
studies were largely limited to hV~ 2-3 eV and a correspondingly small set
of molecular ions.
We have examined the photodissociation of H2, HD+, D , D20+, OD+
ND3 and ND2 , all of which should have exothermic channels with hV - 6.4
eV. In this brief report, we can only summarize several striking
conclusions. Neither of the anticipated products (ND+ and D+) from ND2 is
observed. By contrast, both ND2 and ND+ fragments are detected from ND3 ,
although the latter process is endothermic for cold ND4. The dissociation
processes of OD+ to 0+ + D or D+ + 0 are almost isoergic, if all products
are in their ground states. We observe only 0+. It is not clear at this
time which upper state is responsible for the dissociation. Clearly, our
preliminary results are demonstrating that details of the potential energy
curves well beyond simple energetics will be necessary to interpret these
observations.
221
VIII. HIGH-RESOLUTION LASER-rf SPECTROSCOPY WITH ATOMIC AND MOLECULAR BEAMS
Introduction
The atomic-beam laser-rf double-resonance technique, devised in
1975-1976, provides a way for making extremely precise measurements of energysplittings in atomic or molecular systems. It has been used extensively since
then for the systematic investigation of the hyperfine structure (hfs) ofmetastable states of neutral atoms, and much of the key work has been done atArgonne. Except for a single feasibility study, however, no effort had been
made to use the powerful new technique for the study of challenging molecularstructure problems. In 1979 we selected the alkaline-earth monohalide
radicals for a comprehensive study with this method and in the 3 years since
then great progress has been made. The vibrational, rotational, and isotopic
dependence of many of the spin-rotational and hfs "constants" have beenmeasured to high precision for the calcium monohalide series, clearly
displaying a systematic, monotonic dependence on halide atomic number. For anumber of the parameters measured, no previous information was available for
any molecule of the class. New methods were devised to extend themeasurements to excited states, and the work has stimulated theoretical abinitio calculations to understand these "single-electron-outside-closed-
shells" molecular radicals. In the coming year, a major effort will be made
to undertake measurements of the electric dipole moments of these molecules.Such information, because of the very direct nature of its dependence on theelectronic wave functions, should be particularly valuable for a theoretical
understanding of the electronic states.
a. Hyperfine Structure of the Excited A 2n State of CaF
(W. J. Childs, David R. Cok, and L. S. Goodman)
The hfs spiittings of the A 2n excited state of CaF were found in
our early publications (1979-1980) to be too small to be measured with the
techniques then available. Our shift in 1981-1982 to digital data acquisition
and installation of a much more stable interferometer system for incremental
frequency measurement made observations of such small splittings (1--4 MHz) in
excited states possible, though still difficult. Measurements were carried
out both for the 2n3/2 and 2n1/ 2 states, and a definite J dependence was
observed. In addition, observations over a wide range of values of the
rotational quantum number N show a clear N-dependence. The theoretical
analysis is not yet complete.
Figure VIII-1 shows laser fluorescence spectra for the A211 / 2
X2E1/2 (at left) and A213/2 - X2E1/2 (at right) transitions in CaF. The
slight difference in the splitting of the P component shows that the A-state
hfs is J-dependent.
INCREMENTAL LASER
300 150 0
V2 j
I a
0 0 0
LASER WAVELENGTH(AT X6061.80)
FREQUENCY (MHz)
450 300 IOI
u
zuJzLU(9ZLU
LU
0:D-JLl.
Fig. VIII-l. Laser-induced fluorescence associated with the A 111/2 ++ X E1 /2 (left) and
A2 13/2 ++ X21/ 2 (right) transitions in CaF. The extremely small size of the hyperfine structure in
the excited A-state follows from the fact that the two spectra are nearly the same. A slight
difference in the splitting of the P transition gives evidence that they are not identical, however.
0
0~* V2v2
0o 2() 212
LASR AVLEGT
AT X635.50
223
b. The Hyperfine Structure of Alkaline-Earth Monohalide Radicals:New Methods and New Results, 1980-1982 (W. J. Childs)
A review paper summarizing- the present sta-: of our knowledge of the
spin-rotation and hyperfine interactions in the alkaline-earth monohalide
radicals was written and accepted for publication in Comments on Atomic and
Molecular Physics during the year. All work, from the first free-molecule
observations in 1980 up to the present is covered, and the enormous imprint of
the laser-rf double-resonance technique is made clear. The large body of
precise observations presented show systematic trends with respect to the
vibrational and rotational states and with respect to the halide atom (Z) or
isotope (A) chosen. New theoretical ag initi. work, stimulated by this body
of experimental results, is now underway jointly at Argornne and Northwestern
University.
c. New Line Classifications in Ho I Based on High-Precision hfsMeasurements of Low Levels (W. J. Childs, David R. Cok, andL. S. Goodman)
The hyperfine structure of all four members of the 4f'1 6s2 4I ground
term of Ho I was measured to high precision as a first step in a series of
several experiments to improve our understanding- of the 4f shell. The program
was stimulated by the new capability of carrying out multi-configuration
relativistic ab initio calculations in the rare-earth region. The possibility
of achieving a significantly better understanding of the different
contributions of relativity and configuration interaction to the hfs is now
real, and is of very special interest in the rare earth region because of the
collapse of the 4f shell near Z - 56. The Ho work also succeeded in
identifying- several very strong- previously unclassified "mystery" lines in the
Ho I optical spectrum. In addition, the study confirmed the finding- of other
recent work that the value of <r-3>4f associated with the electric-quadrupole
hfs is significantly smaller for configurations with a 4f11 core than fo'.
those with a 4f10 core. The origin of the effect is not yet understood, but
may be evidence of different Sternheimer shielding- for the two cases. A paper
on this work has been published in J. Opt. Soc. Amer. 73, 151 (1983).
224
'I. Modification of Apparatus for Electric-Dipole MomentMeasurement through the Stark Effect (L. S. Goodman)
Considerable effort has gone into preliminary design work for the
molecular Stark-effect-rf region to be introduced between the two laser-
molecular beam interaction regions of the double-resonance apparatus. An
extremely homogeneous d.c. electric field in which rf or microwave transitions
can be induced (1 MHz to 20 GHz) is required, and it must be thoroughly
shielded from the earth's magnetic field to prevent complications due to the
Zeeman effect. A satisfactory design concept has now been achieved and is
ready for detailing.
225
IX. BEAM-FOIL RESEARCH AND COLLISION DYNAMICS OF HEAVY IONS
Introduction
Our program consists of investigations of the structure anddynamics of atomic ions principally using photon detection techniques. The
experiments involve fast ion beams produced at either the Tandem-Linac
accelerator (30--500-MeV ion energy) or the Argonne Dynamitron accelerator
(0.5--4.5-MeV ion energy) or a low energy "test-bench" facility (0.02--0.12-
MeV ion energy). Laser excitation of the fast beams is anticipated in
future experiments to study atomic structure principally of low ionization
stages.
In 1982, the principal investigator, H. G. Berry, was in Europe
until the end of July; part of the time was spent at the Aim& Cotton
Laboratory, Orsay, France, learning laser techniques, and part of the time
at the University of Lund doing beam-foil spectroscopy with a small Tandem
accelerator.
The program at Argonne continued with a graduate student, JonHardis,* assisted by Professors A. E. Livingstont and L. J. Curtis* duringtheir frequent visits to Argonne. This work involved two atomic structureproblems in neon, plus a continuation of our study of electron channelplategeometries for More efficient data collection.
We have started our program of studies on the interactions of fastion beams with lasers. An argon-ion pump laser and a CW ring dye laser with
frequency-doubling capability have just been delivered. Initial experiments
on collinear laser-fast ion beam resonant excitation are under construction.
*Thesib student, University of Chicago, Chicago, IL.tUnivrsity of Notre Dame, Notre Dame, IN.*University of Toledo, Toledo, OH.
a. Lamb Shifts and Fine Structures of n = 2 in Helium-like Ions(H. G. Berry and J. E. Hardis*)
Following our successful calculations and experiments in silicon,
sulfur and chlorine of the ls2s3Sl - ls2p3P0,2 transition wavelengths, we
have continued this work in several directions:
(i) We are preparing a precision measurement in helium-like
titanium of the same transition. An initial run is scheduled at the Argonne
Tandem-Linac in early 1983. (See Fig. IX-1.)
(ii) A precision measurement in helium-like neon has been
completed at the Argonne Dynamitron. This experiment involved the use of an
*Thesis student, University of Chicago, Chicago, Illinois.
226
48 9+ 216 MeV
300
250
200
400
WAVELENGTH (A)
Fig. IX-i. Preliminary spectrum of 216-MeV titanium. The two-electronTi XXI transition is noted.
Ti xxi 3S1 P 2
389.6 A
(00c0II II
C c
-C0 x_II x x
(0 c 0-II x
c -x IIx cx
x- x
(I)
zD0
150
0
C
II I(IC
X X
00
ii
100
50
0300 500 600
. . . . . . . . . . . . . . . . . . . .
227
8 MeV Ne2 + beam from the Dynamitron. The work should clarify some
discrepancies in recent measurements from other laboratories on these
transitions 1s2s3S1 - 1s2p3 P0, 2 and give a useful test of our two-electron
Lamb-shift calculations. The data are being analyzed.
(iii) We have improved our calculations of the total energies of
the two states 1s2s 3S and ls2p 3P for ions of low Z (Z < 10). We find
significant discrepancies in some previously published results. A
theoretical group at Oxford, England, (Grany et al.) have verified our
earlier calculations for these energies at higher Z.
b. Precision Wavel ngth Measurements in Helium (H. G. Berry,P. Juncar,* H. T. Duong-,* and R. Damaschini*)
In an experiment at Orsay, France, we have used saturated
absorption spectroscopy and a sigmameter to obtain the absolute wavelengths
of the 2p 3P0,1 ,2- 3d 3D1,2,3 transitions near 587.6 rn in 4 He I. Our
precision is about 8 parts in 109. By comparing- with recent two-photon
measurements of direct excitation from the 2s 3S1 level, we obtain values
for the wavelengths of the 2s 3S1 - 2p 3P0,1,2 transitions. Precise
calculations for these transitions are compared with experiment. In
particular, we have analyzed the QED and relativistic corrections.
*Laboratory of Aim& Cotton, Orsay, France.
c. Position-Sensitive Detector for UV Spectroscopy (J. E. Hardis*and H. G. Berry)
We continue to investigate designs of one-dimensional position-
sensitive detectors for the exit focus of our UV spectrometer. A
microchannel plate (MCP) serves as a front-end photon detector and signal
amplifier. Techniques for imaging the output electron signal of the MCP are
under study. Nonlinearities and drift in carbon-resistive-anode readouts
*Thesis student, University of Chicago, Chicago, IL.
228
limit theprecision of the effective spectral dispersion curve obtained.
Conductive wedges appear to hold promise, and computer modeling- is
underway. Application of digital VLSI technology and multi-anode techniques
are also under review.
d. High-spin States in Neon (J. E. Hardis,* A. E. Livingston,tL. J. Curtis,* and H. G. Berry)
Past experiments in this laboratory have identified the quartet
(1s2s2p 4 PO - 1s2p2 4 P) and quintet (1s2s2p2 5 P - 1s2p3 5S) transitions in
carbon, nitrogen, and oxygen. Higher beam energie- at the Dynamitron,
needed to excite the same doubly-excited states in heavier elements, were
not available. We have now a good source (2--3 uiA) of doubly-charged neon
for the Dynamitron accelerator. This effectively doubles the terminal
voltage for that projectile. The quartet spectral lines have been located,
and measurements of their wavelengths and lifetimes have been completed.
The quintet states have been identified and measurements of their
wavelengths and lifetimes are in progress.
*Thesis student, University of Chicago, Chicago, IL.
tUniversity of Notre Dame, Notre Dame, IN.
*University of Toledo, Toledo, OH.
e. Multicharged Ions.at the Dynamitron (J. E. Hardis,* R. Amrein,W. Ray and H. G. Berry)
In addition to upgrading the Dynamitron terminal voltage, we have
attempted to increase the energy of certain beams by producing multicharged
ions directly at the ion source. Tests with a Penning ion source have thus
far been disappointing. However, by careful adjustment of gas pressures and
mixtures (e.g., of Ne and H2), an rf ion source has given reasonable
quantities of well-focussed beams of Ne2+ and Arn+ with n - 2, 3, and 5.
Other rare gas ions should also be feasible. Addition of a crossed-field
analyzer at the source is expected to purify the higher charged beams.
*Thesis student, University of Chicago, Chicago, Illinois.
229
f. Measurement of the Transition Probability of Singlet-TripletIntercombination Lines in Neon (L. J. Curtis*, J. E. Hardist,R. L. Brooks and A. E. Livingston*)
Using the same doubly-charged neon beam mentioned above, we have
measured the lifetimes of the neon 1s 2 2s3p 3P 0 , 1 , 2 states. The J - 1 state
has only about half the lifetime of the other two, and this difference is
attributed to the extra decay channel to the 1s22s2 IS state, accessible to
it alone. The smaller value for J = 1 is due to a J-allowed decay channel
to 2s2 10, and implies a transition probability of 4.3(6) x 108 sec-1 for
this intercombination line. These measurements extend similar measurement
of lighter elements done previously at lower energies (at Lund, Sweden).
This purely relativistic phenomenon is more pronounced in neon than in the
lighter elements.
*University of Toledo, Toledo, OH.
tThesis student, University of Chicago, Chicago, IL.
*University of Notre Dame, Notre Dame, IN.
g. Optical Measurements of Molecular-Ion Fragmentation (H. G. Berry,
L. Engstr5m,* S. Huldt,* and I. Martinson*)
In an experiment in Lund, Sweden, we observed the break-up of fast
CN+ ions in thin carbon foils. CH- was accelerated in a 3-MV Pelletron
Tandem accelerator and charge-exchanged to CN+ at the center gas stripper to
produce, typically, 100 nA of 5-MeV CN+ ions on target. Light yields from
several transitions in high ionization stages of C and N were observed to
vary as a function of carbon foil thickness. For very thin foils the
neighboring fragment ion is close enough to influence and enhance the
excited state production in these ions. The work is continuing both at
Argonne and at Lund. (See Fig. IX-2.)
*University of Lund, Sweden.
230
10
5 10 15 20 25 30f" 50FOIL THICKNESS (/p.g* cm 2 )
Fig. IX-2. Carbon-foil thickness dependence of carbon-ion and nitrogen-ion light yields for 5-MeV incident CN+ molecular ions.
0. C] Y385, 2p P - 3d D
XX N 628A 3s2S-4p2PXx
xx x x x x
x
I II I I I
CI[ 459, A2s2p3P-2s3d3D
0 S
I I I2 I
NIM 765A 2s S-2s2p Px
-xxx x x x X
SNIY 927A 2s2p 3P-2p2 3P
0 0
8
12
10
8
16
12
w
z
- 8
w 12
10
812
10
231
X. INTERACTIONS OF FAST ATOMIC AND MOLECULAR IONSWITH SOLID AND GASEOUS TARGETS
Introduction
Tightly collimated beams of molecular ions with energies variable inthe range 0.5--4.5 MeV are directed onto thin (''100 A) foil or gaseoustargets. The distributions in energy and angle are measured with highresolution (~0.005* and ~300 eV) for the resultant collisionally-induceddissociation fragments. The major aim of the work is a general study of theinteractions of fast ions with matter, but with emphasis on those aspectsunique to the use of molecular-ion projectiles. In addition, we are able tostudy of the structures of the incident molecular ions. These two differentaspects of the work are mutually interdependent. In order to derive structureinformation about a given molecular ion, one needs to know details about theway the dissociation fragments collectively interact with the target in whichthe dissociation occurs. Similarly, a knowledge of the structure of theincident molecular clusters is important in understanding the physics of theirinteractions with the target. We have therefore begun our work with carefulstudies involving beams of the simplest and relatively well understooddiatomic molecular ions (H2+, HeH+, etc.). Even with these, several new andinteresting- phenomena have been encountered (e.g., the interactions betweenthe molecular constituents and the polarization oscillations that they inducein a solid target,, the marked differences in dissociations induced in gases ascompared with those in foils, the anomalously high transmission of somemolecular ions through foils, and striking electron capture phenomena whencompared to atomic ions). As our understanding of these phenomena develops,we plan to go on to studies involving ever more complex projectile ions.
In the course of developing techniques for determining thestereochemical structures of molecular projectiles by coincident detection ofdissociation fragments, preliminary data have shown us the important problemswhich need to be addressed in order to obtain precise structuralinformation. Most prominently, these problems include the need for a moredetailed understanding of the physical processes involved in the interactionsof these fast molecular ions with solid targets and the formation of finalelectronic states. This year we concentrated our efforts on studying theformation of high Rydberg atoms when fast ions exit solids. These atoms werefound to emerge with high probability when fast molecular-ion beams dissociatein foils. Our work was aimed at understanding the processes which lead to theformation of these atoms. Also this year, we demonstrated that K-vacancyequilibration lengths for fast ions traversing solids are much longer thanpreviously anticipated. This was an important confirmation of our model forthe observed charge-state dependence of angular multiple-scattering widths forsuch ions.
Some of the highlights in 1982 included:
232
a. Contribution of Field-Ionized Rydberg Atoms to Convoy ElectronSpectra (D. S. Gemmell, Y.-Z. Gu, E. P. Kanter, D. Schneider,Z. Vager, and B. J. Zabransky)
A prominent feature observed in the energy spectrum of electrons
emitted in the forward direction from thin foils and gas targets under
bombardment by fast ions is a sharp cusp-shaped peak occurring at an energy
where the electron velocity matches the velocity of the emerging projectile
ions. For fast light ions, these "cusp" electrons were believed to originate
from the capture of target electrons into projectile-centered continuum
states. Intense experimental and theoretical efforts have been directed
towards understanding the measured cusps in terms of various theories of this
so-called electron-capture-to-the-continuum (ECC) model, as well as a
competing "wake-riding" model. To date, none of these various theoretical
treatments has had any success in explaining the full range of experimental
data now available from cusp-electron measurements. In pursuing our efforts
to explain some puzzling features of molecular-ion dissociation experiments
which had suggested the production of large numbers of high Rydberg atoms in
fast beams, we have also tried to determine the extent to which the presence
of significant numbers of such atoms could be affecting observations of cusp
electrons.
If electron capture can occur into continuum states lying just above
the ionization threshold of the projectile, there seems to be no a_ priori
reason why capture into bound states lying just below the ionization threshold
cannot also occur with comparable probability. The fate of Rydberg atoms
emerging from a target can be expected to depend sensitively, and in ways
difficult to predict, upon details of the experimental apparatus. Rydberg
atoms have long radiative lifetimes, but they can be ionized in quite modest
electric fields. Certainly the electric fields used in most electron
specrometers suffice to ionize a large fraction of Rydberg atoms entering the
spectrometer. Because it is customary in measurements of cusp electrons to
pass the projectiles emerging from the target through a spectrometer, it is
likely that field-ionizing Rydberg atoms will contribute electrons, traveling
with the beam velocity, to the secondary electron spectrum.
233
In our initial experiments, we incorporated a deflecting field
intermediate between the target and electron spectrometer. By jointly
sweeping the voltages on the deflecting plates, and the electron spectrometer,
we found that although electrons emerging from the target were eliminated as
anticipated by the deflecting field, there existed a sizable contribution of
beam-velocity electrons which originated after the deflecting field. Further
measurements with a +60 volt bias on the foil target shifted the cusp
electrons to lower energy and allowed a separation of the target "cusp" from
the field-ionizing Rydberg contribution.
We have further studied the systematics of this phenomenon with
various ion beams (both atomic and molecular), targets, beam energies, and
experimental geometries. Quite recently, we extended these measurements to
include highly energetic heavy-ion beams. Using the Argonne Tandem-Linac
heavy-ion accelerator, we studied the field ionization of high Rydberg- (n >
300) sulphur ions produced by beam-foil excitation of a 125-MeV sulphur
beam. That experiment conclusively demonstrated a very high yield of such
atoms as had been suspected from previous studies of the delayed x-ray
emission of these fast heavy ions.
These measurements, demonstrating- the large yield of Rydberg atoms
formed in excited fast ion beams, have far-reaching consequences in several
areas of atomic collision physics. Most importantly, many measurements of
charge-state yields and charge-changing cross sections must be reinvestigated
in the light of this discovery.
b. Microwave Field Ionization of Fast Rydberg Atoms (P. Arcuni,*D. S. Gemmell, E. P. Kanter, P. M. Koch,t D. R. Mariani,tD. Schneider, W. van de Water,t and B. J. Zabransky)
In an attempt to determine the quantum-state populations for beam-
foil excited high Rydberg atoms, we have collaborated with a group from Yale
University in studying the microwave ionization of such atoms. WOE used a
*Thesis student, University of Chicago, Chicago, Illinois.
tYale University, New Haven, Connecticut.
234
750-keV H++80 volts target bias
Fig. X-1. A joint distribution of 00 electrons showing energy spectra forvarious levels of microwave power (watts). The lower-energy peak,unaffected by microwave power, is caused by convoy electrons. Thehigher-energy peak, which grows with power, is produced by field-Lo&ization of Rydberg atoms in the microwave cavity. At lower power,there is an additional contribution from atoms ionizing in thespectrometer field (170 v/cm).
235
9.91-GHz microwave cavity to ionize Rydberg atoms after production in a thin
carbon foil, but before entering the electron spectrometer field used to
energy-analyze the resulting electrons. Because of its high frequency, the
variable microwave electric field had only a negligible effect on the energy
spectrum of electrons originating prior to the cavity. By applying a bias
voltage to the foil target, we were able to separate clearly those electrons
produced at the target from those created in the cavity. An additional
contribution was observed from field ionization in the spectrometer field when
the microwave field was reduced below the magnitude of that field. (See
Fig. X-1.)
This experimental geometry separates the ionizing field from the
analyzing field, allowing us to vary the former to much higher values than we
had been able to achieve before. With a microwave power of 18.4 watts, we
achieved a maximum electric field of about 2.8 kV/cm which would ionize
hydrogen atoms as low as n = 24. Analysis of the data so far seems to
indicate that the n population is consistent with a simple OBK-type last-layer
capture process. It is hoped that a better understanding of the microwave
ionization process will yield more detailed information about the distribution
of kinetic energy of the electrons that we observe.
c. Coherent Stark States in Foil-Excited Fast Rydberg Atoms(D. S. Gemmell, E. P. Kanter, D. Schneider, and Z. Vager)
In a further effort to determine the quantum-state population of
foil-excited fast Rydberg atoms, we studied the field ionization of these
atoms in a variety of field geometries. One finding is that transverse
electric fields are more effective in ionizing such atoms than are
longitudinal fields. This is a strong indication of high alignment in the
excitation and suggests an electron density in these states which is oblate
with respect to the bean direction. A very surprising finding was the
observation of oscillations in the ionization yield when a longitudinal
electric field, starting at the target, is varied in magnitude. (See Fig. X-
2.) These oscillations are regularly spaced, with a period that varies with
the beam energy. We have demonstrated that these observations imply coherent
excitation of a few Stark levels near the unshifted center of the Stark
236
FIELD PERIOD (V/cm)
8 2 10 5 2800C-f -.
6 0.75-MeV H+ (a) (d) 0.75-MeV4 F 0.8 V/cm 0.8- H .
2000 -0.4
-20Ot
8000-6 1.5-MeV H+ (b) 2. - I.5-MeV ~4 AF= t 1.2V/cm 1.6- H
200 1.2
0.8400 VVV10.4-
8006 3.0-MeV H+ (C)_ 16- (f) 3-MeV
AF= 3.OV/cm 12 H -
8--2 4-40-
-80 -40 0 40 80 0 0.2 0.4 0.6 ..LONGITUDINAL FIELD (V/cm) FIELD FREQUENCY (V/cm)
Fig. X-2. A comparison of differential yield curves as a function oflongitudinal field for three different proton bombarding energies,(a) 0.75 MeV, (b) 1.5 MeV, and (c) 3 MeV, in the region between 100 V/cm.The square-wave fields, AF, are shown in each. The Fourier powerspectrum for each energy is shown in (d), (e), and (f), respectively.The Fourier spectra are computed from the full range of data measuredfor each energy.
237
manifold. The observed modulations are extremely sensitive to the amplitudes
of the coherently excited states. This phenomenon offers a new and
potentially powerful technique for studying excitation mechanisms that produce
high Rydberg- states of fast projectiles as they exit solids.
d. Equilibration Lengths of K-Vacancy Production in Solids(E. P. Kanter, D. Schneider, and B. J. Zabransky)
Measurements on the angular distributions of fast ions traversing
foils have shown a pronounced dependence of the multiple-scattering widths
upon the charge state of the emerging- ions. We have successfully explained
these results in terms of the large scattering angles achieved by those ions
that bear K vacancies. A quantitative model has been developed which
demonstrates how the "memory" of K-vacancy producing collisions gives rise to
large multiple-scattering widths in spite of apparent charge-state
equilibration. The K-shell capture and loss cross sections are an important
input to this model. Because these cross sections are largely unknown, we
have conducted a series of experiments to determine the K-shell charge-
exchange equilibration lengths for fast ions in foils. By measuring the yield
of KLL Auger electrons from 0.4- and 2.7-MeV W+ ions exiting solid carbon
targets, we have demonstrated that indeed the K-equilibration lengths are
longer than had been previously assumed, confirming our model of the multiple-
scattering- data.
e. Analysis of Molecular-Ion Stopping Power Measurements(D. S. Gemmell, E. Johnson,* E. P. Kanter, and M. F. Steuer)
Following the discovery in 1974 of the influence of cluster effects
upon the slowing- down of ions in solids, there have been several experimental
and theoretical investigations of this phenomenon. In general, the cluster
stopping powers for light projectiles such as H2+ are fairly well described on
the basis of wake models derived from Lindhard's dielectric function. The
situation for heavy clusters, however, appears to be more complex.
*Graduate student, Oxford University, England.
238
We have measured the stopping power ratio of N+ fragments from equal
velocity beams of N+ and N2 +. In contrast with the earlier work on light
ions, we were able to select molecular N+ fragment pairs that were
"longitudinally" aligned to the beam direction upon exiting the foil. This
orientational selectivity greatly simplifies the analysis.
Surprisingly, the results show that, contrary to the light ion data,
the stopping power of heavy molecular clusters is diminished relative to of
the corresponding monatomic projectiles. This implies that most of the
induced negative polarization charge must lie between the separating fragment
ions.
An intense effuzc to explain these data has yielded only limited
success. We have learned that it is vital to use a non linear wake model for
such heavy diatomic ions. To avoid the complexities of a proper quantum-
mechanical treatment we have employed a semiclassical calculation of free-
electron scattering- by two screened ionic cores to compute the stopping forces
as the ions traverse the solid. This method has had success in describing our
highest energy (3-MeV) stopping data, however, several problems limit the
applicability of this approach.
239
XI. THEORETICAL ATOMIC PHYSICS
Introduction
Our studies on the effects of relativity and electron correlationsin atomic processes consist of five major parts, three of which involve casestudies of atomic processes in the discrete, autoionization and continuumspectra, and two of which deal with the development of new techniques foratomic calculations.
(1) Rydberg Series Interactions in Ar, Kr and Xe Isc electronicSequences. Recent experiments on the absorption spectrum of Ba in theBeutler-Fano resonance region have opened up possibilities for studying-systematic trends of autoionization and Rydberg- series interactions alongisoelectronic sequences. In particular, the observed Ba++ spectrum is verydifferent from that of neutral Xe, showing- rapid changes in resonance profileswith increasing- nuclear charge. Theoretical spectra for Xe-like ions havebeen obtained with relativistic random-phase approximation (RRPA)calculations, and they are in very good agreement with experiment.Eigenchannel analysis of these spectra has revealed important information onthe influence of increasing nuclear charge on Rydberg- series interactions, andon the intimate relationship between electron correlation, term dependence andautoionization. A model is proposed to explain the system trend of resonanceprofiles in terms of the competition between atomic central potentials andelectron correlation effects along isoelectronic sequences. We shall makesimilar studies of the theoretical spectra for Ar- and Kr-like ions in theresonance region. Since the central potentials of these ions are differentfrom those of Xe-like ions, these studies can provide further tests of theproposed model.
The spectrum of Ba++ in the region of 5p+ns, nd discrete excitationsis also available experimentally. There are large variations in theintensities of absorption lines along Rydberg- series, reflecting strongchannel interaction effects. We shall employ the RRPA to provide ab initiodata for an eigenchannel analysis of the discrete spectrum of Ba+. Thisshould give important insights into the effect of Rydberg- series interactionson the observed line intensities.
(2) 4f Orbital Collapse for Pd-Like Ions. Because of thecompetition between the atomic central potential and the centrifugal barrier,the effective potential of f orbitals consists of an inner and an outer wellseparated by a potential barrier. For low Z ions, the 4f orbital resides inthe outer well and stays away from the atomic core. For Z > 58, it suddenlycollapses into the core region when the inner well is deep enough to support abound state. This sudden decrease in energy and size of the 4f orbital leadsto the filling of the 4f shell and the formation of the rare earths, and has aprofound influence on the spectra of these elements. Our recent study on theabsorption spectra of Xe-like ions in the region of 4d+nf, Cf excitationsshowed that orbital collapse is basically a shape resonance effect arisingfrom the interaction between the eigenstates of the inner well with those ofthe outer well. In particular, the observed Ba+ spectrum cqn be explained interms of the partial collapse of the 4f orbital in the 4d+f P channel. Weshall carry out further tests of our model of orbital collapse by studying- the
240
absorption spectra of Pd-like ions with a combination of the relativisticrandom-phase approximation and the term-dependent Hartree-Fock techniques. Asneutral Pd (Z=46) is further away from the region where orbital col p e takesplace, and as Pd has a rather simple ground-state configuration (rd S), weshould be able to make detailed studies of the spectra of Pd-like ions and togain better understanding of the collapse phenomenon along isoelectronicsequences.
(3) Hyperfine Structures of Rare Earth Elements. Importantinformation on the dynamics of many-electron correlation effects andrelativity can be obtained from atomic hyperfine structure studies.Traditionally, diagrammatic many-body perturbation theories are used toaccount for electron correlations and Dirac-Fock techniques are used to studyrelativistic effects on hyperfine structures. We shall attempt to study thecombined effect of electron correlations and relativity from amulticonfiguration Dirac-Fock (MCDF) point of view.
Our initial goal is to provide ab initio radial matrix elementswhich can be compared with experimental measurements. We shall study thehyperfine structures of rare earth element such as Ho Z = 7) and Er (Z =68) with ground state configurations of 4f 6s2 and 4f 2 6s , respectively.The chemical properties of the rare earths are determined mainly by the 4forbital which is known to go through a sudden decrease in energy and size (theso called "collapse" of the 4f orbital) at the beginning of this group ofelements. Atomic hyperfine structures of these elements can provide importantinformation on the properties of the collapsed 4f orbitals.
(4) Relativistic Phase Amplitude Method. The phase amplitudemethod describes the asymptotic behavior of continuum wave functions in termsof a relationship between the phase and the amplitude functions. Theamplitude function is in turn determined by a nonlinear equation derived fromthe Schridinger equation. This method is an important technique indetermining phase shifts and normalization factors of continuum wavefunctions, and in computing relevant matrix elements. It is also closelyrelated to many-body techniques such as the R-matrix theory and the closed-coupling method in atomic scattering calculations. We shall generalize thismethod to include four-component relativistic continuum wave functions. Thisis a first step towards a relativistic distorted wave Born approximationcalculation, which is useful, for example, for electron-impact-excitationcalculations involving highly stripped ions, and for inner-shell Augertransition studies.
(5) Multiconfiguration Relativistic Random-Phase Approximation.Starting from the time-dependent variational principle and amulticonfiguration Dirac-Fock ground state, we have obtained a set ofgeneralized RRPA equations which reduce to the usual RRPA equations when thereis only one configuration in the ground state. We are applying this newtechnique to low-energy photoionization studies, and eventually toautoionization studies in conjunction with the multichannel quantum defecttechnique. Our initial goal is to study the photoionization spectrum of Ba,where the usual RRPA technique is not quite capable of explaining the observedspectrum.
241
a. Transitions Between Quartet States of Three-Electron Ions(K. T. Cheng and H. G. Berry)
Transitions between the qua:tet states of (ls2snt) for nt = 4d, 4f,
5f and 5g are studied using a multiconfiguration Dirac-Fock (MCDF)
technique. These are satellite lines of the strong (ls2s2p)4P - (ls2s)4 P
transitions and are observed in the beam-foil spectrum of C3+. We found that
the coupling of the outer nL electrons with the (ls2s)3S and the (1s2p)3P
cores is weak, and that there are large deviations from the LS-coupling scheme
even for light ions such as C3+.
b. Influence of Increasing Nuclear Charge on the Rydberg Spectra ofXe, Cs' and Ba" (W. T. Hill III,* K. T. Cheng, W. R. Johnson,tT. B. Lucatorto,* T. J. Mcllrath,* and J. Sugar*)
The spectra of Xe, Cs+ and Ba++ in the region of Beutler-Fano
autoionization resonances are studied with a combined theoretical-experimental
effort. Theoretical resonance profiles are obtained from a relativistic
random-phase appv-ximation (RRPA) calculation. Systematic trends in the
resonance profiles are analyzed with the Multichannel Quantum Defect Theory
(MQDT). Our study demonstrates the intimate connection between electron-
electron correlation, term dependence and autoionization and underscore the
power of MQDT in analyzing complex spectra.
*National Bureau of Standards, Washington, DC.
tUniversity of Notre Dame, Notre Dame, Indiana.
*University of Maryland, College Park, Maryland.
c. Collapse of the 4f Orbital for Xe-Like Ions (K. T. Cheng andC. Froese Fischer*)
The effect of 4f orbital collapse on the spectra of Xe-like ions in
the region of 4d+nf, Ef excitations is studied using a term-dependent Hartree-
*Vanderbilt University, Nashville, Tennessee.
242
Fock technique. We found that the collapse phenomenon is basically a shape
resonance effect and that it is strongly term dependent. Also, the spectra of
Xe-like ions are determined mainly by the collapse of the 4f orbital in the
4d+f 1P channel. In particular, partial collapse of the 4f orbital is
responsible for the appearance of strong resonance lines in the observed Ba++
spectrum, thereby resolving the controversy regarding the interpretation of
this spectrum.
d. Photoionization of the Inner 4d Shells for Xe-Like Ions(K. T. Cheng and W. R. Johnson*)
Photoionization of the inner 4d shells for Xe, Cs+, Ba++ and La3+ is
studied using the relativistic random-phase approximation. Total cross
sections, partial cross-section branching ratios and angular distribution
asymmetry parameters are calculated, and their systematic trends along the
isoelectronic sequence are studied. Important dynamic effects of electron
correlations are obtained from an eigenchannel analysis. We, found that there
are shape resonances in the effective potential for f electrons, and that the
collapse of the 4f orbital along the isoelectronic sequence is closely related
to changes in f orbitals in passing through these resonances.
*University of Notre Dame, Notre Dame, Indiana.
e. Energy Level Scheme and Transition Probabilities of C R-Like Ions(K.-N. Huang,* Y.-K. Kim,* K. T. Cheng and J. P. Desclauxt)
The multiconfiguration Dirac-Fock technique is used to calculate
thirty-one low-lying levels of Ce-like ions. Breit interaction and Lamb shift
contributions are calculated perturbatively as corrections to the Dirac-
Fock energies. Probabilities for the El, Ml and E2 transitions connecting
excited levels with the ground levels are presented. These data are useful in
astrophysics and in controlled fusion research.
*Radiological and Environmental Research Division, ANL.
tCentre d'Etudes Nucleaires de Grenoble, Grenoble, France.
243
XII. ELECTRON SPECTROSCOPY WITH FAST ATOMIC AND MOLECULAR-ION BEAMS
Introduction
The study of inner-shell ionization phenomena arising in energetic
ion-atom collisions has been a field of experimental and theoretical interest
for many years. The experimental techniques of high-resolution electron andx-ray spectroscopy coupled with the availability of intense well-collimated,highly-monoenergetic beams of a great variety of atomic and molecular ionic
species at MeV energies, have opened many new avenues of research into inner-shell ionization phenomena. Although most of the early experiments were
performed under single-collision conditions (dilute gas targets), it has
recently been demonstrated that a wealth of valuable additional information
can be obtained when solid targets (thin foils) are employed. For studies
involving low-Z atoms (Z < 20), the spectroscopy of Auger electrons isespecially favored because of the low fluorescence yields.
The emission of Auger electrons following the dissociation of gas-and foil-excited fast (MeV) molecular-ion beams is investigated by measuring
single-electron spectra with high resolution. The spectra from ionic
fragments produced using molecular-ion beams are compared with spectra
produced using monatomic ion beams of the same velocity.
High-resolution Auger electron spectroscopy on target and projectile
species permits the study of excitation and transition probabilities fordifferent projectiles. In the case of He, for example, autoionizing stateshave been shown to interfere with continuum states. The interference pattern,
observed from the shapes of the lines observed in the electron spectrum,depends strongly on the electron observation angle and on the projectile
velocity, and charge state. From angle-dependent high-resolution measurements
it is possible to deduce the phase shift between the transition amplitudes forthe resonant (autoionization) and non-resonant (direct ionization)processes. If, in addition to the ion-beam excitation, a laser is used forselective excitation or for the "pumping" of excited states in the projectileor target atom, it should permit spectroscopy oa "exotic" states that can onlybe produced in violent ion-atom collisions. The advent of intense tunablelaser light sources has now made such experiments possible, e.g., the laser
could prepopulate specific outer-shell target states which subsequentlyinteract with a fast ion beam, producing inner-shell vacancies. This two-step
excitation process may enhance the creation of those short-lived autoionizingand Auger states that are not efficiently former in ion-atom collisionprocesses without lasers.
a. Investigation of Rydberg States Formed in Foil-Excited Fast Ion Beams(D. S. Gemmell, E. P. Kanter, D. Schneider, Z. Vager, and B. J. Zabransky)
We have extended our investigation of the formation of bound states
with high principal quantum numbers (Rydberg states) in a variety of fast,
foil-excited ion beams. Different field arrangements including microwave
244
fields have been applied to study the effect of field ionization of these
states. The yields of electrons produced via field ionization in the analyzer
were measured for a variety of atomic and molecular-ion beams. In the case of
125-MeV s14+ we have measured the absolute yield (for n z, 250) to be
~10-5/projectile. This value is consistent with recent findings of a group in
Munich who studied delayed K x-ray emission.
From our measurements it is clear that the neglect of the influence
of field-ionized Rydberg atoms in previous studies of convoy electrons may
have led to conflicting results when experiment and theory have been
compared. We also found that the contribution of electrons due to capture
into Rydberg states increases if molecular ions are used rather than atomic.
The higher probability for forming Rydberg states in the molecular case might
also account for unusual effects seen in the energy and angular distribution
of fragment ions following the dissociation of fast molecular ions in foil
targets.
The initial work has been followed by experiments in which the
ionizing field and the analyzing field are separate and can be varied
independently. For this purpose a microwave field was applied to the beam
prior to its entrance into the spectrometer. The microwave cavity was
designed so that the electrons emitted from the target could pass through the
high-frequency field with minimal disturbance. A large increase in the yield
of electrons due to field ionization was observed with increasing microwave
power. This demonstrated very impressively the high probability for forming
Rydberg states in fast ion beams penetrating foil targets. The maximum power
that could be applied to the cavity was 8 W corresponding to a maximum
longitudinal field of 2.4 kV/cm. This field is capable of ionizing hydrogenic
Rydberg states down to about n n 21.
To test the effect of field ionization in further detail, a
longitudinal electrostatic field was applied. The stripping field was
followed by a weak transverse field which enabled us to deflect target
electrons out of the spectrometer viewing region. Field ionization of the ion
beam could then be performed before the beam entered the analyzer field. By
using a digital lock-in technique (a small oscillating field was superimposed
on the longitudinal field) the differences in the ionization rates in the
245
spectrometer field were monitored. It was possible to resolve some
oscillatory structure in the yield curves. A transverse magnetic field also
allowed comparison of the dependence of the field ionization rate on the
direction of the field. It was found that transverse fields are much more
effective in field ionization than are the longitudinal fields. This is a
strong indication of high alignment in the excitation, suggesting an oblate
electron density in these Rydberg states with respect to the beam direction.
b. Inner-Shell Vacancy Fractions in Foil-Excited Ion Beams(P. J. Cooney, E. P. Kanter, D. Schneider, and B. J. Zabransky)
K-shell fractions for 2.7- and 0.4-MeV nitrogen ions exiting thin
carbon foils were measured as a function of foil thickness. The vacancy
fractions per projectile ion were deduced from measuring the yields of K-Auger
electrons emitted by the foil-excited nitrogen ions. It was found that the
vacancy fractions for these ions reach equilibrium only for foils thicker than
~'20 pg/cm2. The variation of the vacancy fractions in foils with thicknesses
below 20 hg/cm2 is a strong function of the projectile energy (Fig. XII-1). A
similar experiment was performed at the Argonne tandem accelerator with 45-MeV
F5+ ions. The results were found to be consistent with those for the nitrogen
case. Vacancy production cross sections derived from experiments with such
thin targets should be reconsidered in light of this finding.
c. Laser-Stimulated Ar L-Shell Excitation in Slow Ion-Atom Collisions
We have studied Ar L-shell excitation in slow heavy ion-atom
collisions for a large variety of collision systems. These studies have
confirmed that inner-shell vacancy production in systems where the ion
velocity is smaller than that of the relevant inner-shell orbital velocities
can be understood as electron promotion via coupliings between different
molecular orbitals (MO's) formed during the collision process. We plan to
perform experiments where we investigate the influence of L-shell vacancies in
systems like N + Ar or Ar + Ar due to additional photon excitation and/or
ionization of the quasimolecule formed in slow heavy ion-atom collisions.
246
' I I ' I
_ 1.6 IT: * MMWel_ .6 - ...-- - - - - - - - - 1 -
0 I
z 'I-
o I.4
- -j--0.4 MeV
z -- X-- 2.7MeVI 1.2
1.0 I ' I0 20 40 60 80 100
TARGET THICKNESS (pg/cm2)
Fig. XIl-1. K-vacancy fractions for nitrogen projectiles leaving carbonfoils as a function of foil thickness. Data is shown for 0.4- and2.7-MeV emergent ions. The solid and dashed curves result from fitsto the experimental data with a functional form
YK(x) = a /v(1--x/o).
247
d. Simultaneous Laser- and Ion-Beam Excitation of a Na Vapor Target
We plan to investigate the L-shell autoiontzation spectra of Na and
Na+ and the Na K-shell Auger-electron spectrum with simultaneous laser- and
ion-beam excitation. One goal of this study is to investigate whether
simultaneous laser/ion beam excitation can improve spectroscopic accuracy and
resolution. In the experiment a laser is used to excite the Na vapor from the
ground state to the Na*(ep) 2 P 3 / 2 state. Then a He+ beam at MeV energies will
be used for the L-shell excitation of the Na. Depending on whether the laser
is in or out, the probability for the excitation (and deexcitation), of the
Na L-shell should be different and detectable from the corresponding line
intensity. The sodium K-shell Auger-spectrum will also be measured as a
function of projectile energy and species to study multiple ionization.
e. Further Investigations of the Formation of Rydberg States in FastIon Beams
The experimental results on the formation of Rydberg states in fast
ion beams have opened many new questions. We intend to explore the mechanisms
leading to the formation of these states as fast ions exit solids. The
spectroscopy of these sta -s will be pursued using specific field arrangements
and microwave and/or laser spectroscopy techniques.
f. Study of Li-and He-Autoionization as a Function of Projectile Velocityand Charge State
The helium autoionization spectrum will be studied as a function of
Li-projectile charge state, the electron observation angle and the projectile
velocity. The goal is to examine the interference between a resonant process
(autoionization) and nonresonant process (direct ionization) both leading to
the same final (ionic) state. This interference can be studied from an
analysis of the asymetric line profiles. By applying theoretical model
calculations we expect to obtain the phase shift between the two relevant
transition amplitudes and the ratio of the amplitudes. The study will
therefore provide a test of the theoretical descriptions.
248
The investigation of the Li-autoionization spectrum following the
excitation of MeV Li-ions in various targets should give insight into the
formation of the excited states of Li in such collisions. In particular the
formation of Li- is of interest since it is a candidate for further
investigation involving laser-spectroscopy.
g. Auger-Electron Production Following Ion Collisions in Solids
The investigation of Auger-electron production following light- and
heavy-ion bombardment of solids will be continued. Reliable absolute yield
measurements will be the first goal of these studies. It should be possible
to deduce escape lengths for selected Auger-electrons. The latter will
involve measurements under channeling conditions to control the emission depth
of the electrons.
249/)b5-
PUBLICATIONS FROM 1 APRIL 1982 THROUGH 31 MARCH 1983,AND STAFF-MEMBERS OF THE PHYSICS DIVISION
251
PUBLICATIONS FROM 1 APRIL 1982 THROUGH 31 MARCH 1983
The list of "journal articles and book chapters," is classified bytopic; the arrangement is approximately that followed in the Table ofContents of this Annual Review. The "reports at meetings" includeabstracts, summaries, and full texts in volumes of proceedings; they arelisted chronologically.
A. JOURNAL ARTICLES AND BOOK CHAPTERS
Isospin Effects in Pion Single-Charge-Exchange ReactionsD. Ashery, D. F. Geesaman, R. J. Holt, H. E. Jackson, J. R.Specht, K. E. Stephenson, R. E. Segel (Northwestern), P.Zupranski (Northwestern), H. W. Baer (LANL), J. D. Bowman(LANL), M. D. Cooper (LANL), M. Leitch (LANL), A. Erel (TelAviv. U.), R. Chefetz (Tel Aviv U.), J. Comuzzi (MIT), R. P.Redwine (MIT), and D. R. Tieger (Boston U.)
Phys. Rev. Lett. 50, 482, (1983)
Isospin Splitting of the Giant Dipole Resonance in 60NiT. J. Bowles, R. J. Holt, H. E. Jackson, R. D. McKeown, A. M.Nathan (U. Illinois), and J. R. Specht
Phys. Rev. Lett. 48, 986 (1982)
Erratum: Isovector Radiavie Decays and Second-Class Currents in Mass 8Nuclei [Phys. Rev. C 18, 1447 (1978)]
T. J. Bowles and G. T. GarveyPhys. Rev. C 26, 2336 (1982)
Measurement of the 7 Be(p,Y)8B Reaction Cross Section at Low EnergiesB. W. Filippone, A. J. Elwyn, C. N. Davids, and D. D. Koetke(Valparaiso U.)
Phys. Rev. Lett. 50, 412 (1983)
Demgstration of the Need for Meson Exchange Currents in the Beta Decayof N(O)
C. A. Gagliardi, G. T. Garvey, J. R. Wrobel, and S. J. Freedman(Stanford U.)
Phys. Rev. Lett. 48, 914 (1982)
Erratum: Beta-Alpha Angular Correlations in Mass 8 [Phys. Rev. C 22, 738(1980)]
R. D. McKeown, G. T. Garvey, and C. A. GagliardiPhys. Rev. C 26, 2336 (1982)
Observation of the (i~, nrn) and (i+,,ir+p) Reactions at 165 MeVE. Piasetsky (Tel Aviv U.), A. Altman (Tel Aviv U.), J.Lichtenstadt (Tel Aviv U.), A. I. Yavin (Tel Aviv U.), D.Ashery, W. Bertl (ETH, Zurich), L. Felawka (ETH, Zurich), H. K.Walter (ETH, Zurich), F. W. Schlepotz (U. Zurich), R. J. Powers(U. Zurich), R. G. Winter (U. Zurich and C. of Wm. and Mary),and J. v. d. Pluym (Vrije U., Amsterdam)
Phys. Lett. 114B, 414 (1982)
252
Pion-Induced Nucleon Knockout Reactions on 160 and 180E. Piasetzky (Tel Aviv U.), A. Altman (Tel Aviv U.), J.Lichtenstadt (Tel Aviv U.), A. I. Yavin (Tel Aviv U.), D.Ashery, W. Bertl (ETH, Zurich), L. Felawka (ETH, Zurich), H. K.Walter (ETH, Zurich), F. W. Schlepitz (U. Zurich), R. J. Powers(U. Zurich), R. G. Winter (U. Zurich and C. of Wi. and Mary),and J. v. d. Pluym (Vrije U., Amsterdam)
Phys. Rev. C 26, 2702 (1982)
Study of the 3 9 ,41K(d, 3He) 38 ,40 Ar Reactions at 22.8 MeVC. M. Bhat (Bangalore U., India), M. Raja Rao (Bangalore U.),N. G. Puttaswamy (Bangalore U.), and J. L. Yntema
Nucl. Phys. A394, 109 (1983)
7Li(d,p)8Li Reaction Cross Section Near 0.78 MeVA. J. Elwyn, R. E. Holland, C. N. Davids, and W. Ray, Jr.
Phys. Rev. C 25, 2168 (1982)
Absolute Cross Section for 7Li(d,p)8Li and Solar Neutrino Capture RatesB. W. Filippone, A. J. Elwyn, W. Ray, Jr., and D. D. Koetke(Valparaiso U., Indiana)
Phys. Rev. C 25, 2174 (1982)
y Decay of States in 4 7 CrG. Hardie (Western Mich. U., Kalamazoo, MI), S. A. Gronemeyer,L. Meyer-Schitzmeister, and A. J. Elwyn
Phys. Rev. C 26, 456 (1982)
180Tag,m Production Cross Sections from the 1 80Hf(p,n) ReactionEric B. Norman, Timothy R. Renner, and Patrick J. Grant (U.Washington, Seattle, WA)
Phys. Rev. C 26, 435 (1982)
Prompt Compound Nuclear K x Rays in Fusion Reactions Induced by a HeavyProjectile
H. Ernst, W. Henning, C. N. Davids, W. S. Freeman, T. J.Humanic, M. Paul, S. J. Sanders, F. W. Prosser, Jr. (U.Kansas), and R. A. Racca (U. Kansas)
Phys. Lett 119B, 307 (1982)
Search for Transient Electric Field Gradients Acting on Fast-Moving Ionsin Solids
H. Ernst, W. Henning, T. J. Humanic, T. L. Knoo, Steven C.Pieper, and J. P. Schiffer
Phys. Rev. C 26, 2039 (1982)
Reactions to Resolved States and to Non-fusion Channels for 160 + 4 8 Caat Elab = 158.2 MeV
T. J. Humanic, H. Ernst, W. Henning, and B. ZeidmanPhys. Rev. C 26, 993 (1982)
253
Nuclear Radiation
Dennis G. KovarMcGraw-Hill Encyclopedia of Science and Technology, 5thedition, ed. by S. P. Parker (McGraw-Hill, NY, 1982), pp.320-321
Nuclear Reaction
Dennis G. Kovar
McGraw-Hill Encyclopedia of Science and Technology, 5thedition, ed. by S. P. Parker (McGraw-Hill, NY, 1982), pp.322-326
Inelastic Scattering and One-Neutron-Transfer Reactions of 180 + 40CaK. E. Rehm, W. Henning, J. R. Erskine, and D. G. Kovar
Phys. Rev. C 26_, 1010 (1982)
Inelastic Scattering of 1 60 from 40,42,44,48CaK. E. Rehm, W. Henning, J. R. Erskine, D. G. Kovar, M. H.Macfarlane, S. C. Pieper, and M. Rhoades-Brown
Phys. Rev. C 25, 1915 (1982)
Strong Popy at n of Excited 0+ States in Even Zr Isotopes Observedwith the ( C, 0) Reaction
Wolfgang Mayer (Technische Universitg't Munchen, Garching, W.
Germany), D. Pereira (TUM, Germany), K. E. Rehm (TUM, Germany),H. J. Scheerer (TUM, Germany), H.J. K6rner (TUM, Germany), G.Korschinek (TUM, Germany), Waltraud Mayer (TUM, Germany), P.
Sperr (TUM, Germany), Steven C. Pieper, and R. D. LawsonPhys. Rev. C 26, 500 (1982)
High Spin States in 9 4Ru and 95Rh
A. Amusa (PHY/U. Ife) and R. D. LawsonZ. Phys. A 307, 333 (1982)
Relativistic Quantum Mechanics of Particles with Direct InteractionsF. Coester and W. N. Polyzou (MIT)
Phys. Rev. D 26, 1348 (1982)
Coherence, Mixing, and Interference Phenomena in Radiative J DecaysIsaac Cohen (Weizmann Inst., Israel), Nathan Isgur (U.Toronto), and Harry J. Lipkin
Phys. Rev. Lett. 48, 1074 (1982)
Isospin Dependence of Pion Absorption on 3 HeT.-S. H. Lee and K. Ohta (MIT, Cambridge)
Phys. Rev. Lett. 49, 1079 (1982)
Microscopic Study of the A-Nucleus Potential from a Many-BodyHamiltonian for Tr, N and A
T.-S. H. Lee and K. Ohta (MIT, Cambridge)Phys. Rev. C 25 3043 (1982)
254
Angular Momentum Paradoxes with Solenoids and MonopolesHarry J. Lipkin and Murray Peshkin
Phys. Lett. 118B, 385 (1982)
Isotope Targets Prepared by Vapor DepositionG. E. Thomas
Nucl. Instrum. Methods 200, 27 (1982)
High Intensity Inverted Sputter SourceJ. L. Yntema and P. J. Billquist
Nucl. Instrum. Methods 199, 637 (1982)
Yrast (h 11/2)n Excitations in Proton-Rich N=82 NucleiH. Helppi (Purdue U.), Y. H. Chung (Purdue U.), P. J. Daly(Purdue U.), S. .R. Faber (Purude U.), A. Pakkanen (Purdue U.),I. Ahmad (CHM), P.Chowdhury, Z. W. Grabowski, T. L. Khoo, R. D.Lawson, and J. Blomqvist (Res. Inst. Phys., Stockholm)
Phys. Lett. 115B, 11 (1982)
Transitigfrom Collective to Aligned-Particle Configurations at HighSpin in Dy
A. Pakkanen (Purdue U.), Y. H. Chung (Purdue U.), P. J. Daly(Purdue U.), S. R. Faber (Purdue U.), H. Helppi (Purdue U.), J.Wilson (Purdue U.), P. Chowdhury, T. L. Khoo, I. Ahmad (CHM),J. Borggreen, Z. W. Grabowski, and D. C. Radford (Yale U.)
Phys. Rev. Lett. 48, 1530 (1982)
Search for Structure in the Fusion of 160 + 2 4MgR. A. Racca (U. of Kansas), F. W. Prosser (U. of Kansas), C. N.Davids, and D. G. Kovar
Phys. Rev. C 26, 2022 (1982)
Photoionization Mass Spectrometry of NH2OH: Heats of Formation of HNO+and NOH+
R. E. Kutina, G. L. Goodman and J. BerkowitzJ. Chem. Phys. 77, 1664-1676 (15 Aug. 1982)
Photoionization Mass Spegtrometr of CH3SH, CD34 H and CH3SD: Heats ofFormation of CH3S (CH2SH ), CH2S , CH2S and HCS
R. E. Kutina, A. K. Edwards, G. L. Goodman and J. BerkowitzJ. Chem. Phys. 77, 5508-5526 (1 Dec. 1982)
Hyperfine Structure of the X 2E Ground State of Ca35C1 and Ca 3 7 C1 byMolecular-Beam Laser-rf Double Resonance
W. J. Childs, David R. Cok, and L. S. GoodmanJ. Chem. Phys. 76, 3993-3998 (15 April 1982)
Hyperfine Structure of the A 2r State of Ca 3 5 C1W. J. Childs, David R. Cok, and L. S. Goodman
J. Opt. Soc. Am. 72, 717-719 (June 1982)
255
Vibrational, Rotational, and Isotopic Dependence of CaBr X 2E Spin-Rotational and hfs Parameters
W. J. Childs, David R. Cok, and L. S. GoodmanJ. Mol. Spectrosc. 95, 153-156 (1982)
New Line Classifications in Ho I Based on High-Precision Hyperfine-Structure Measurement of Low Levels
W. J. Childs, David R. Cok, and L. S. GoodmanJ. Opt. Soc. Am. 73, 151 (1983)
Doubly Excited States in Some Light AtomsH. Gordon Berry, Robert L. Brooks, Jonathan E. Hardis,and W. J. Ray
Nucl. Instrum. Methods 202, 73-77 (1982)
Comparisons Between Theory and Experiment in Two Electron SystemsH. G. Berry, R. DeSerir. and R. L. Brooks
Nucl. Instrum. and Methods 202, 95-101 (1982)
Beam-Foil SpectroscopyH. G. Berry and M. Hass (Weizman Inst., Rehovot, Israel)
Ann. Rev. Nucl. Part. Sci. 32, 1-34 (1982)
Hyperfine Structures of the nd 1 D(n = 3--8) States of 3He IRobert L. Brooks, Vincent F. Streif and H. Gordon Berry
Nucl. Instrum. Methods 202, 113-117 (1982)
Alignment and Orientation of the 3p 3 P He I Term After Tilted-FoilExcitation
R. L. Brooks, H. G. Berry and E. H. Pinnington (Univ. ofAlberta, Edmonton, Alberta, Canada)
Phys. Rev. A 25, 2545-2549 (1982)
Measurement of the Transition Probability of the 2s2 1S0 -2 s3 p 3P4Intercombination Line in Ne VII
J. E. Hardis, L. J. Curtis, P. S. Ramunujam, A. E. Livingston,and R. L. Brooks
Phys. Rev. A27, 257--261 (January 1983)
Spectroscopie et Mesures de Vies Moyennes de Niveaux de Nickel HautementIonise
C. Jacques (Universite Laval, Quebec, Canada), M. Druetta(Universite de Lyon, Villeurbanne, France), H. G. Berry and E.J. Knystautas (Universite Laval, Quebec, Canada)
Nucl. Instrum. Methods 202, 45-47 (1982)
Energies of Some Triplet Levels in 4He IP. Juncar (Lab. Aime Cotton, France), H. G. Berry, R.Damaschini (Lab. Aime Cotton), and H. T. Duong (Lab. AimeCotton)
J.Phys. B: At. Mol. Phys. 16, 381 (1983)
256
Collisional Effects in the Passage of Fast Molecular Ions Through ThinFoils
Donald S. GemmellNucl. Instrum. Methods 194, 255 (1982)
Ion-Source Dependence of the Distributions of Internuclear Separationsin 2-MeV HeH+ Beams
Elliot P. Kanter, Donald S. Gemmell, Itzhak Plesser, and ZeevVager
Nucl. Instrum. Methods 194, 307 (1982)
Diminished Stopping Power for Fast Nitrogen and Oxygen Diclusters inCarbon
Malcolm F. Steuer, Donald S. Gemmell, Elliot P. Kanter, EdwardA. Johnson, and Bruce J. Zabransky
Nucl. Instrum. Methods 194, 277 (1982)
Influence of Increasing Nuclear Charge on the Rydberg Spectra of Xe, Cs+and Ban: Correlation Term Dependence, and Autoionization
W. T. Hill III (NBS), K. T. Cheng, W. R. Johnson (U. of NotreDame), T. B. Lucatorto (NBS), T. J. Mcllrath (U. Maryland), andJ. Sugar (NBS)
Phys. Rev. Lett. 49, 1631 (1982).
Correlation and Relativistic Effects in Spin-Orbit SplittingsK.-N. Huang (RER), Y.-K. Kim (RER), K. T. Cheng, and J. P.Desclaux (Grenoble)
Phys. Rev. Lett 48, 1245 (1982).
Target--Thickness Dependence of K-Shell Vacancy Fractons in Foil-ExcitedIon Beams
D. Schneider, E. P. Kanter, and B. J. ZabranskyPhys. Rev. A 26, 3700-3701 (1982)
257
B. PUBLISHED REPORTS AT MEETINGS
Proceedings of the International School of Physics "Enrico Fermi", Varenna,Italy, 23 June-5 July 1980.
Brueckner-Bethe Calculations of Nuclear MatterB. D. Day
Course LXXIX ed. by A. Molinari (North-Holland,Amsterdam, 1981), pp. 1-71
Proceedings of the Netherlands Physical Society 1980 International SummerSchool on Nuclear Structure, Dronten, The Netherlands, 12-23 August 1980.
Nuclear Structure and Heavy-Ion ReactionsJohn P. Schiffer
Ed. by K. Abrahams, K. Allaart, and A. E. L. Dieperink(Plenum, NY, 1981), pp. 127-163
Proceedings of the Ninth World Conference of the International Nuclear
Target Development Society, Gatlinburg, Tennessee, 13-16 October 1980
Isotope Targets Prepared by Vapor DepositionG. E. Thomas
Ed. by E. H. Kobisk and H. L. Adair (North-Holland,1982), pp. 27-31 [Reprinted from Nucl. Instrum. Methods200, 27 (1982)]
Proceedings of the Sixth International Conference on Fast Ion BeamSpectroscopy, Laval, Quebec, Canada, 17-20 August 1981
Doubly Excited States in Some Light AtomsH. Gordon Berry, Robert L. Brooks, Jonathan E. Hardis,and W. J. Ray
Ed. by E. J. Knystautas and R. Drouin (North-Holland,1982) +Nucl. Instrum. Methods 202, 73 (1982)
Comparisons Between Theory and Experiment in Two Electron SystemsH. G. Berry, R. DeSerio, and R. L. Brooks
Ed. by E. J. Kynstautas and R. Drouin (North-Holland,
1982) +Nucl. Instrum. Methods 202, 95-101 (1982)
Hyperfine Structures of the nd 1 D(n = 3--8) States of 3 He IRobert L. Brooks, Vincent F. Streif, and H. Gordon Berry
Ed. by E. J. Kynstautas and R. Drouin (North-Holland,1982)+Nucl. Instrum. Methods 202, 113 (1982)
Spectroscopie et Mesures de Vies Moyennes de Niveaux de NickelHautement Ionise
C. Jacques (U. of Laval, Quebec), M. Druetta (U. of Lyon,France), H. G. Berry, and E. J. Knystautas (U. Laval)
Ed. by E. J. Kynstautas and R. Drouin (North-Holland,1982)+Nucl. Instrum. Methods 202, 45 (1982)
258
Proceedings of the 1981 Annual Meeting of the Optical Society of America,Kissimmee, Florida, 26-30 October 1981
Photoionization of Atoms and MoleculesJ. Berkowitz
J. Opt. Soc. Am. 71, 1579 (1981)
Proceedings of the U.S.-Japan Seminar on Charged-Particle PenetrationPhenomena, Honolulu, Hawaii, 25-29 January 1982
"Interactions of Fast Molecular Ions Traversing Thin Foils" - "TheContribution from Field-Ionized Rydberg Atoms in Measurements onConvoy Electrons"
Donald S. GemmellNational Technical Information Service, Springfield,Virginia, 1983), CONF-820131, pp. 222-255
Proceedings of the Conference on Lasers in Nuclear Physics, Oak Ridge,Tennessee, 21-23 April 1982
On-Line Laser Spectroscopy with a Cooled He-Jet Transport SystemDavid Lewis (Iowa State U.), Rollin Evans (Iowa State), CaryDavids, Miles Finn (U. Minnesota), George Greenlees(Minneosta), and Stanley Kaufman (Minnesota)
Ed. by C. E. Bemis, Jr. and H. K. Carter (HarwoodAcademic Publishers, NY, 1982), pp. 189-196
APS Meeting, Washington, D.C., 26-29 April 1982
Elastic Scattering and Reactions of 40Ca + 4 0 CXaR. R. Betts (CHM Div., ANL), I. Ahmad (CHM), B. B. Back(CHM), B. G. Glagola (CHM), W. Henning, S. Saini (CHM), andJ. L. Yntema
Bull. Am. Phys. Soc. 27, 474 (1982)
usionil 28n 2Seep-InelasticReaction Cross Sections for
H. Ernst, C. N. Davids, W. S. Freeman, W. Henning, T.Humanic, F. W. Prosser (U. Kansas), and R. Racca (Kansas)
Bull. Am. Phys. Soc. 27, 475 (1982)
Measurement of the Beta Decay.of 16N(0-, 120 keV): The Need for
Meson Exchange Currents and the Value of gC. A. Gagliardi, G. T. Garvey, S. J. freedman (Stanford), andJ. R. Wrobel
Bull. Am. Phys. Soc. 27, 492 (1982)
Fundamental Aspects of Nuclear Beta DecayG. T. Garvey
Bull. Am. Phys. Soc. 27, 463 (1982)
259
APS, Washington, D.C., 26-29 April 1982 (contd.)
Search for Transient Electric Field Gradients Acting on Fast-Moving Ions in Solids
T. J. Humanic, H. Ernst, W. Henning, T. L. Khoo, Steven C.Pieper, and J. P. Schiffer
Bull. Am. Phys. Soc. 27, 520 (1982)
T0F Mea urements of Evaporation Residues Produced in 160 + 12C and60 + 2 Mg at 4 S 9.4 MeV/A
T. Humanic, D. G. Kovar, R. Betts (CHM Div., ANL), P.Chowdhury, D. Henderson, R. V. F. Janssens, W. Khn, and K.Wolf (CHM)
Bull. Am. Phys. Soc. 27, 478 (1982)
A gular9 omentum Dependence of Neutron Spectra in the 250-MeVNi + Zr Reaction
W. Kuhn, I. Ahmad (CHM Div., ANL), P. Chowdhury, R. V. F.Janssens, T. L. Khoo, F. Haas (Mich. State U.), J. Kasagi(MSU), and R. M. Ronningen (MSU)
Bull. Am. Phys. Soc. 27, 475 (1982)
Energy Dependence of 2 4Mg + 2 4Mg Elastic Scattering and ReactionsS. Saini (CHM Div., ANL), R. R. Betts (CHM), I. Ahmad (CHM),B. B. Back (CHM), G. B. Glagola (CHM), J. L. Yntema, R. W.Zurmuhle (U. Penn.), and F. Haas (Mich. State U.)
Bull. Am. Phys. Soc. 27, 480 (1982)
Measurement of the 2 H(Y,n) 1 H Relative Cross Section at EY S 19 MeVK. Stephenson, R. E. Holland, R. J. Holt, H. E. Jackson, R.D. McKeown, and J. R. Specht
Bull. Am. Phys. Soc. 27, 570 (1982)
High Intensity Inverted Sputter SourceJ. L. Yntema and P. J. Billquist
Bull. Am. Phys. Soc. 27, 521 (1982)
30th Annual Conference on Mass Spectrometry and Allied Topics, Honolulu,Hawaii, 6-11 June 1982
Photoionization Mass Spectrometry of CH3SH, CD3SH and CH SD:Heats of Formation of CH3S(CH2 SH), CH2S , CH2S and HCS
R. E. Kutina, A. K. Edwards, G. L. Goodman, and J. BerkowitzProc. ed. by F. W. Lampe (American Soc. for MassSpectrometry, 1982), Abstracts, pp. 617-618
Phojoionization Mass Spectrometry of NH20H: Heats of Formation ofHNO and NOH
R. E. Kutina, G. L. Goodman, and J. BerkowitzProc. ed. by F. W. Lampe (American Soc. for Mass
Spectrometry, 1982), Abstracts, pp. 504-505
260
30th Annual Conference on Mass Spectrometry and Allied Topics, Honolulu,Hawaii, 6-11 June 1982 (contd.)
Photoelectron Spectra of Gas Phase Lanthanide TrihalidesB. M. Ruscic, G. L. Goodman, and J. Berkowitz
Proc. ed. by F. W. Lampe (American Soc. for MassSpectrometry, 1982), Abstracts, pp. 700-701
Proceedings of the 1982 INS International Symposium on Dynamics of NuclearCollective Motion--High Spin States and Transitional Nuclei, Tokyo, Japan,6-10 July 1982
Shell Structure at High Spin and the Influence on Nuclear ShapesT. L. Khoo, P. Chowdhury, I. Ahmad (CHM Div., ANL), J.Borggreen, H. Emling, D. Frekers, R. V. F. Janssens, A.Pakkanen (Purdue U.), Y. H. Chung (Purdue), P. J. Daly(Purdue), S. R. Faber (Purdue), Z. Grabowski (Purdue), H.Helppi (Purdue), M. Kortelahti (Purdue), and J. Wilson(Purdue)
Ed. by K. Ogawa and K. Tanabe (Inst. for Nucl. Study, U.of Tokyo, Japan, Sept. 1982), pp. 256-274
International Conference on X-Ray and Atomic Inner-Shell Physics, Eugene,Oregon, 23-27 August 1982
The Effect of Inner-Shell Vacancies on Multiple ScatteringDistributions of Heavy-Ion Beams Traversing Solids
E. P. KanterEd. by B. Crasemann (U. of Oregon, 1982) Program andAbstracts, Vol. 1, pp. 132-133
Equilibration Lengths for K-Shell Charge-Exchange Processes forFast Ions Traversing Foils - Evidence from Multiple-ScatteringDistributions and Auger-Yield Measurements
Elliot P. Kanter, Dieter Schneider, and Donald S. GemmellEd. by B. Crasemann (American Inst. of Physics, NY,1982) pp. 735-744+ Program and Abstracts (U. of Oregon, 1982), Vol 1, p.169
Auger-Electron Spectroscopy on Foil and Gas Excited Fast-Atomicand Molecular-Ion Beams
D. Schneider, E. P. Kanter, D. S. Gemmell, and B. J.
ZabranskyEd. by B. Crasemann (U. of Oregon, 1982)Program and Abstracts, Vol. 2, pp. 186-187
SNEAP '82 (Symposium of Northeastern Accelerator Personnel, Seattle,Washington, 6-8 Oct. 1982)
1982 SNEAP Tandem-Linac Accelerator ReportP. Den Hartog, R. Pardo, F. Munson, and C. Heath
Ed. by W. G. Weitkamp (Univ. of Washington, 1982), pp.166-168
261
SNEAP '82 (Symposium of Northeastern Accelerator Personnel, Seattle,Washington, 6-8 Oct. 1982) (contd.)
A Terminal Lens for an FN TandemP.K. Den Hartog, F. H. Munson, and C. E. Heath
Ed. by W. G. Weitkamp (Univ. of Washington, 1982), pp.84-91
Ion Source Development at ArgonneP.J. Billquist and J. L. Yntema
Ed.by W. G. Weitkamp (Univ. of Washington, 1982), pp.261-267
American Physical Society, Division of Nuclear Physics, Amherst,Massachusetts, 14-16 October 1982
Fusion of 6 4Ni Beams Incident on the Even Sn IsotopesW. S. Freeman, D. F. Geesaman, W. Henning, W. Kuhn, J. P.Schiffer, B. Zeidman, and F. W. Prosser (U. Kansas)
Bull. Am. Phys. Soc. 27, 707b (1982)
Measurement of the Ti Half-Life Via Tandem Accelerator MassSpectrometry
D. Frekers, W. Henning, W. Kutschera, K. E. Rehm, R. K.Smither, J. L. Yntema, and B. Stievano (INFN, Legnaro, Italy)
Bull. Am. Phys. Soc. 27, 712 (1982)
Fragmentation of High-Spin Particle-Hole States in 26MgD. F. Geesaman, B. Zeidman, C. Olmer (Indiana U.), A. D.Bacher (Ind. U.), G. T. Emery (Ind. U.), C. W. Glover (Ind.U.), H. Nann (Ind. U.), W. P. Jones (Ind. U.), S. Y. van derWerf (KVI, Groningen), R. E. Segel (Northwestern U.), and R.A. Lindgren (U. Mass., Amherst)
Bull. Am. Phys. Soc. 27, 697 (1982)
Electroproduction of HypernucleiT.-S. H. Lee and J. P. Schiffer
Bull. Am. Phys. Soc. 27, 719 (1982)
Mea grements of Transverse Electron Scattering Cross Sectionsin Mg
R. A. Lindgren (U. Mass., Amherst), M. A. Plum (U. Mass.), R.L. Huffman (U. Mass.), R. S. Hicks (U. Mass.), X. K. Maruyama(NBS, Wash., D.C.), A. D. Bacher (Ind. U.), C. Olmer (Ind.U.), D. F. Geesaman, and B. H. Wildenthal (Mich. State U.)
Bull. Am. Phys.Soc. 27, 697 (1982)
American Physical Society, New York, New York, 24-27 January 1983
Nuclear Physics with Several-GeV ElectronsGerald Garvey
Bull. Am. Phys. Soc. 28, 50 (1983)
262
American Physical Society, New York, New York, 24-27 January 1983 (contd.)
High Spin State in NucleiT. L. Khoo
Bull. An. Phys . Soc. 28, 50 (1983)
263f26+i
C. ANL PHYSICS DIVISION REPORTS
GeV C. W. Electron Microtron Design Reported. by H. E. Jackson
Argonne National Laboratory Topical ReportANL-82-22 (May 1982)
A National CW GeV Electron Microtron Laboratoryed. by H. E. Jackson
Argonne National Laboratory Topical ReportANL-82-83 (December 1982)
265
STAFF MEMBERS OF THE PHYSICS DIVISION
Listed below are the permanent staff of the Physics Division for the yearending 31 March 1983. The program heading indicates only the individual'scurrent primary activity.
EXPERIMENTAL NUCLEAR PHYSICS AND ACCELERATOR PHYSICS
Scientific Staff
Lowell M. Bollinger, Ph.D., Cornell University, 1951
tEugene P. Colton, Ph.D., University of California, Los Angeles, 1968
*Edwin A. Crosbie, Ph.D., University of Pittsburgh, 1952
Cary N. Davids, Ph.D., California Institute of Technology, 1967
Alexander J. Elwyn, Ph.D., Washington University, 1956
I Melvin S. Freedman, Ph.D., University of Chicago, 1942
Stuart J. Freedman, Ph.D., University of California, 1972
Gerald T. Garvey, Ph.D., Yale University, 1962
Donald F. Geesaman, Ph.D., State University of New York,
Stony Brook, 1976
**Walter F. Henning, Ph.D., Technical University, Munich, 1968
ttRobert E. Holland, Ph.D., University of Iowa, 1950
Roy J. Holt, Ph.D., Yale University, 1972
$*Harold E. Jackson, Jr., Ph.D., Cornell University, 1959
*In charge of tandem-superconducting linac operations and the ATLAS project.
tAccelerator research group. Joined the Physics Division October 1, 1982.
No longer at Argonne as of November 1982. Present address: Los Alamos
National Laboratory, Los Alamos, New Mexico.
Accelerator research group. Joined the Physics Division October 1, 1982.
In charge of Dynamitron accelerator operations. No longer at Argonne
as of November 1982. Present address: Fermi National Accelerator
Laboratory, Batavia, Illinois.
IIRetired - research participant.
Joint appointment with the University of Chicago.
Temporarily assigned to Technical University of Munich, Germany
(September 1982--September 1983).
ttRetired - research participant.
**In charge of Design Project for the GeV Electron Microtron.
266
Robert V. Janssens, Ph.D., Universite Catholique de Louvain,
Belgium, 1978
Tat K. Khoe, Ph.D., Technische Hogeschool Delft, Netherlands, 1960
Teng Lek Khoo, Ph.D., McMaster University, 1972
Dennis G. Kovar, Ph.D., Yale University, 1971
Victor E. Krohn, Ph.D., Case Western Reserve University, 1952
Robert L. Kustom, Ph.D., University of Wisconsin, 1969
Walter Kutschera, Ph.D., University of Graz, Austria, 1965
tAlexander Langsdorf, Jr., Ph.D., Massachusetts Institute of Technology,
1937
Richard C. Pardo, Ph.D., University of Texas, 1976
Karl Ernst Rehm, Ph.D., Technical University, Munich, 1973
tG. Roy Ringo, Ph.D., University of Chicago, 1940
*John P. Schiffer, Ph.D., Yale University, 1954
Kenneth W. Shepard, Ph.D., Stanford University, 1970
Lester C. Welch, Ph.D., University of Southern California, 1970
Jan L. Yntema, Ph.D., Free University of Amsterdam, 1952
Benjamin Zeidman, Ph.D., Washington University, 1957
THEORETICAL NUCLEAR PHYSICS
IlArnold F. Bodmer, Ph.D., Manchester University, 1953
Fritz Coester, Ph.D., University of Zurich, 1944
Benjamin Day, Ph.D., Cornell University, 1963
Dieter Kurath, Ph.D., University of Chicago, 1951
Robert D. Lawson, Ph.D., Stanford University, 1953
*Accelerator Research Group. Joined the Physics Division
October 1, 1982.
tRetired - research participant.
*Associate Director of the Physics Division; Director through
September 1982. Joint appointment with the University of Chicago.
Joined the Physics Division December 13, 1982.
IIJoint appointment with the University of Illinois, Chicago Circle Campus.
267
Tsung-Shung Harry Lee, Ph.D., University of Pittsburgh, 1973
*James E. Monahan, Ph.D., St. Louis University, 1951
tMurray Peshkin, Ph.D., Cornell University, 1951
Steven C. Pieper, Ph.D., University of Illinois, 1970
ATOMIC AND MOLECULAR PHYSICS
Joseph Berkowitz, Ph.D., Harvard University, 1955
H. Gordon Berry, Ph.D., University of Wisconsin, 1967
Kwok-tsang Cheng, Ph.D., University of Notre Dame, 1977
William J. Childs, Ph.D., University of Michigan, 1956
Donald S. Gemmell, Ph.D., Australian National University, 1960
Leonard S. Goodman, Ph.D., University of Chicago, 1952
Elliot P. Kanter, Ph.D., Rutgers University, 1977
I Gilbert J. Perlow, Ph.D., University of Chicago, 1940
Dieter Schneider, Ph.D., Free University of Berlin, 1945
SURFACE SCIENCE--FUSION POWER
"Manfred S. Kaminsky, Ph.D., University of Marburg, 1957
ADMINISTRATIVE STAFF
F. Paul Mooring, Ph.D., University of Wisconsin, 1951
ttJames R. Specht, A.A.S., DeVry Technical Institute, 1964
qOn disability status due to illness.
Deputy Director of the Physics Division.
Temporarily assigned to Laboratoire Aims Cotton, C.N.R.S., Orsay,
France (November 1981--April 1982).
Director of the Physics Division; Associate Director through
September 1982.
IIJoint appointment as Editor of Applied Physics Letters.
Transferred to ANL Materials Science and Technology Division, October 1982.
**Assistant Director of the Physics Division. Retired February 1983.
ttAssistant Director of the Physics Division since March 1, 1983.
268
TEMPORARY APPOINTMENTS
Postdoctoral AppointeesPartha Chowdhury (from State University of New York, Stony Brook,
New York): Gamma-ray spectroscopic studies of high angularmomentum properties in nuclei. (November 1979--January 1983)
David R. Cok (from Harvard University, Cambridge, Massachusetts):
RF and laser spectroscopy of molecular and ionic beams. (September1980--August 1982)
*Bradley W. Filippene (from University of Chicago, Chicago, Illinois):
Nuclear astrophysics research. (December 1982--January 1983)
tCarl A. Gagli di (from Princeon University, Princeton, New Jersey):Study of C beta decay: N(O ) s-decay experiment; design ofneutrino oscillation experiment instrumentation. (June 1982--
August 1982)
William S. Freeman (from State University of New York, Stony Brook,New York): Experimental heavy-ion and charged-particle nuclearphysics. (December 1980-- )
Thomas J. Humanic (from University of Pittsburgh, Pittsburgh,Pennsylvania): Experimental nuclear physics: heavy-ion reactions(transfer, fusion, incomplete fusion, etc.) using Argonne Tandem-Linac. (Argonne 1980--July 1982)
William E. Kleppinger (from Stanford University, Stanford, California):Theory of electromagnetic and weak interactions in nuclearphysics. (November 1982--- )
Wolfgang Kuhn (from Max-Planck-Institut fur Kernphysik, Heidelberg,Germany): Heavy-ion nuclear physics. (May 1981--November 1982)
*Raymond E. Kutina (from University of Toronto, Toronto, Canada):
Photoionization of free radicals. (March 1980--February 1983)
Alan Minchinton (from Flinders University, Adelaide, Australia):Collisional effects in the passage of fast molecular ions through
thin foils and gases. (December 1982-- )
*Formerly Resident Student Associate (Thesis), July 1979 through
December 1982. Ph.D., University of Chicago, 1983.
tFormerly Resident Student Associate (Thesis), July 1977 through
May 1982. Ph.D., Princeton University, 1982.
*No longer at Argonne as of February 28, 1983.
269
James J. Napolitano (from Stanford University, Stanford, California):Experimental studies of weak interactions and associated topics.(May 1982-- )
Ronald S. Pandolfi (from University of California, Los Angeles,California): UV-laser photofragmentation of molecular ions.(December 1982-- )
John A. Parmentola (from Massachusetts Institute of Technology,Cambridge,
Massachusetts): Theoretical research on chiral bag models in thestrong coupling approximation and high-energy proton nucleusscattering. (August 1980-- September 1982)
Volker H. Pfeufer (University of Hannover, Germany): RF laserspectroscopy on atoms, molecules, and ions. (July 1982-- )
Branko M. Ruscic (from Rudjer Boskovic Institute, Zagreb, Yugoslavia):Photoionization and photoelectron spectroscopy. (September 1981--
)
Lawrence P. Somerville (from Lawrence Livermore Laboratory, Livermore,California): Accelerator-based atomic physics: beam-foilspectroscopy; fast laser-ion beam interactions. (January 1983--
)
George S. Stephans (from University of Pennsylvania, Philadelphia,Pennsylvania): Nuclear physics using heavy-ion beams from the ANLlinac. (November 1982-- )
Kenneth E. Stephenson (from University of Wisconsin, Madison,Wisconsin):
Experimental photonuclear and intermediate energy nuclearphysics. (September 1979--July 1982)
Ernst Ungricht (from Eidgenossische Technische Hochschule, Zurich):Medium-energy pion scattering. (November 1982-- )
Robert B. Wiringa (from Los Alamos National Laboratory, Los Alamos,New Mexico): NN interaction, three-body forces, many-body theoryfor light nuclei, nuclear matter and neutron stars. (January 1981-
- )
Long-Term Visitors (at Argonne more than 4 months)
Daniel Ashery (Tel Aviv University, Ramat Aviv, Israel): Experimentalstudies of intermediate energy nuclear physics. (August 1980--October 1982)
270
*Dieter Frekers (University of Munster, Munster, West Germany):
Experimental heavy-ion and charged-particle nuclear physics.(December 1981-- )
tHiroshi Ikezoe (Japan Atomic Energy Research Institute, Tokai-Mura,Japan): Study of the nuclear reaction mechanism induced by the
energetic heavy-ion beams. (October 1982-- )
Hiroshi Kudo (University of Tsukuba, Japan): Accelerator-based atomic
physics. (December 1982-- )
David C. Radford (from Yale University, New Haven, Connecticut):Research on high spin states and heavy-ion reactions. (February1983-- )
$GuntherU. H. Rosner (Max-Planck-InsLitut fur Kernphysik, Heidelberg,Germany): Heavy-ion physics; reaction mechanisms; fusion and
heavy-ion reactions; charged-particle observation; Y-raydeexcitation. (June 1982-- )
tSuehiro Takeuchi (Japan Atomic Energy Research Institute, Tokai-Mura,Japan): Investigation of superconducting linac technology.
(October 1982-- )
Resident Graduate Students
Philip W. Arcuni (University of Chicago, Chicago, Illinois): Electronspectroscopy of ion-atom collisions. (October 1981-- )
Jordan B. Camp (University of Chicago, Chicago, Illinois): Weakinteractions. (October 1982-- )
Rollin M. Evans (Iowa State University, Ames, Iowa): On-line laserspectroscopy of radioactive atoms using the superconductinglinac. (March 1981-- )
Bradley W. Filippone (University of Chicago, Chicago, Illinois):Nuclear astrophysics research. (June 1979--December 1982)
Miles A. Finn (University of Minnesota, Minneapolis, Minnesota):On-line laser spectroscopy of radioactive atoms using thesuperconducting linac. (April 1981-- )
*Deutsche Forschungsgemeinschaft Fellowship.
tU.S.--Japan Collaboration for Nuclear Physics.
$Alexandervon Humboldt Foundation Fellow.
Postdoctoral appointee from December 1982 through January 1983.
271
Carl A. Gagliardi (Pknceton University, Princeton, New Jersey):C beta decay; N(O) -decay experiment; design of neutrino
oscillation experiment instrumentation. (July 1977--May 1982)
Jonathan E. Hardis (University of Chicago, Chicago, Illinois):Ion-ion and ion-atom collisions. (October 1979-- )
Alexandra R. Heath (University of Chicago, Chicago, Illinois): Weakinteractions in nuclear physics. (January 1979-- )
Michael A. Kroupa (University of Chicago, Chicago, Illinois): Searchfor magnetic monopoles using a plastic scintillator array.(July 1982-- )
Wolfram Stoffler (Freie Universitgt, Berlin, Germany): Electronspectroscopy with laser and fast ion-beam interaction.(July 1982-- )
Short-Term Visitors (at Argonne less than 4 months)
A. Faculty
Ademola Amusa (University of Ife, Ile-Ife, Nigeria,2efrica):Shell-model calculations in some nuclei (e.g., 0). (September1982--November 1982)
Reinhard Bruch (Universitst Freiburg, Freiburg, Germany): Electronspectroscopy. (July 1982--October 1982)
Wu Chieh Cheng (Paine College, Augusta, Georgia): High resolutionspectroscopy of ions using lasers (June 1982--August 1982)
Patrick J. Cooney (Millersville State College, Millersville,Pennsylvania): Studies of the interaction of fast-moving ions with
matter. (May 1982--July 1982)
Alan K.Edwards (University of Georgia, Athens, Georgia): UV-laserphoto-fragmentation of molecular ions. (June 1982--August 1982)
Hans Emling (Gesellschaft fur Schwerionenforschung, Darmstadt,Germany): Y spectroscopy of high spin states. (April 1982--June1982)
Geert Jonkers (Free University, Amsterdam, The Netherlands):Photoelectron spectroscopy of short-lived high-temperature species,
especially development of double oven techniques. (May 1982--September 1982)
*Postdoctoral appointee from June 1982 through August 1982.
272
John C. Kelly (University of New South Wales, Australia): Developmentof ion optics for atomic physics and Dynamitron applications.(June 1982--September 1982)
Michael J. King (Michigan State University, East Lansing, Michigan):Relativistic effects in fermionic states--a consistent treatment;connection between the relativistic constraint approach and the
quasipotential method. (July 1982--September 1982)
Stephen Landowne (University of Munich, Munich, Germany):Semimicroscopic and coupled-channel calculations of heavy-ionreactions. (April 1982)
David A. Lewis (Iowa State University, Ames, Iowa): On-line laserspectroscopy of radioactive atoms using the superconducting linac.
*Harry J. Lipkin (Weizmann Institute of Science, Rehovot, Israel):
Angularmomentum in electromagnetic fields of solenoids andmonopoles; applications of the constituent quark model to hadron
spectroscopy. (June 1982--November 1982)
A. Eugene Livingston (University of Notre Dame, Notre Dame, Indiana):Beam-foil spectroscopy of highly-ionized atoms. (August 1982)
Xiuzeng Ma (Institute of Atomic Energy, Beijing, China):Ultrasensitivemass spectrometry. (January 1983--February 1983)
Michael Paul (Hebrew University, Jerusalem, Israel): Accelerator-massspectrometry. (January 1983--September 1982)
P. R. Ramanujam (University of Toledo, Toledo, Ohio): High resolutionspectroscopy of ions using lasers. (August 1982--September 1982)
Ralph E. Segel (Northwestern University, Evanston, Illinois): Nuclearphysics research. (August 1982--September 1982)
Malcolm F. Steuer (University of Gerogia, Athens, Gerogia): Analysisof N2+ molecular ions' stopping power in carbon foils.(June 1982--August 1982)
Zeev Vager (Weizmann Institute of Science, Rehovot, Israel):Population of Rydberg states by swift ions after carbon targets.
(July 1982--October 1982)
*Joint appointment with Argonne High Energy Physics Division and with
Fermi National Accelerator Laboratory, Batavia, Illinois.
273
J. Dirk Walecka (Stanford University, Stanford, California):Scattering of energetic electrons by nuclei. (October 1982--January 1983)
B. Graduate Students
Edward A. Johnson (Oxford University, Oxford, England): Analysis ofmolecular-ion stopping power data and the development of a heavy-ion wake. (June 1982--July 1982)
Robert M. Panoff (Washington University, St. Louis, Missouri): Ground-state energetics of spin-aligned deuterium. (May 1982--August1982)
C. Undergraduate Students
James W. Bales (North Carolina State University, Raleigh, NorthCarolina).
(June 1982--August 1982)
Todd A. Drumm (Westminster College, New Wilmington, Pennsylvania).(January 1983-- )
Dana S. Fine (Stanford University, Stanford, California). (June 1982--August 1982)
James J. Hofmann (East Stroudsburg State College, East Stroudsburg,Pennsylvania) (January 1982--July 1982)
Arnold Kravitz (University of Hartford, West Hartford, Connecticut).(June 1982--August 1982)
John E. Tkaczyk (Rutgers State University, New Brunswick, New Jersey).(June 1982--August 1982)
David B. Young (Hope College, Holland, Michigan). (January 1983-- )
*Argonne Fellow.
274
TECHNICAL AND ENGINEERING STAFF
Ralph Benaroya
Peter J. Billquist
John M. Bogaty
*Patric K. Den Hartog
William F. Evans
John P. Greene
tJoseph E. Kulaga
Bruce G. Nardi
Robert W. Nielsen
Walter Ray, Jr.
James R. Specht
George E. Thomas, Jr.
James N. Worthington
Jerome R. Wrobel
UBruce J. Zabransky
Gary P. Zinkann
* In charge of Tandem accelerator operations.
tNo longer in the Physics Division as of May 1982. Now in the Chemical
Technology Division.
Assistant Division Director as of March 1, 1983.
In charge of Dynamitron accelerator operations.
275
Distribution for ANL-83-25
Internal:
R. AveryE. S. BeckjordL. BurrisD. W. CisselP. M. DehmerM. Derrick
R. E. DieboldD. R. FergusonM. S. Freedman
A. Friedman
B. R. T. FrostT. L. GilbertP. F. GustafsonE. HubermanM. Inokuti
J. H. KittelK. L. KliewerC. E. KlotzA. B. Krisciunas (12)L. G. LeSageR. A. Lewis
P. MessinaE. G. PewittJ. J. Roberts
J. RundoJ. E. SchofieldR. W. SpringerE. P. SteinbergD. Streets
C. E. TillJ. UnikS. WexlerR. S. Zeno
A. AmusaP. W. Arcuni
R. BenaroyaJ. BerkowitzH. G. Berry
A. R. BodmerL. M. BollingerJ. B. CampK.-T. ChengW. J. ChildsF. Coester
E. A. CrosbieC. N. DavidsB. DayP. K. Den HartogDynamit ronS. J. FreedmanW. S. Freeman
D. FrekersG. T. GarveyD. F. GeesamanD. S. GemmellL. S. GoodmanJ. E. HardisA. HeathW. HenningR. J. HoltH. IkezoeH. E. JacksonR. V. JanssensM. S. KaminskyE. P. KanterT. K. KhoeT. L. KhooW. E. KleppingerD. G. KovarV. E. KrohnM. A. KroupaH. KudoD. KurathR. L. Kustom
W. Kutschera
R. D. Lawson
T.-S. H. LeeA. MinchintonJ. E. MonahanJ. J. NapolitanoU. NielsenR. S. PandolfiR. C. PardoG. J. PerlowM. Peshkin (65)V. PfeuferS. C. PieperD. C. RadfordW. H. RauckhorstK. E. RehmG. R. RingoG. RosnerB. M. RuscicJ. P. SchifferK. W. ShepardR. K. SmitherL. P. SomervilleJ. R. SpechtG. S. StephansW. StofflerS. TakeuchiK. J. ThayerG. E. ThomasE. UngrichtL. WelchR. B. WiringaJ. N. WorthingtonJ. L. YntemaB. ZabranskyB. ZeidmanANL Patent Dept.
ANL Contract FileANL LibrariesTIS Files (6)
External:
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276
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277
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278
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279
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280
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282
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The NetherlandsR. H. Siemssen, U. Groningen, The NetherlandsG. van Middelkoop, Vrije Universiteit, Amsterdam, The NetherlandsA. Vermeer, U. Utrecht, The NetherlandsA. Poletti, U. Auckland, New ZealandJ. F. Williams, Queens U., Belfast, Northern IrelandPakistan Inst. of Nuclear Science and Technology, Rawalpindi, PakistanQuaid e=Azam U., Dept. of Physics, Islamabad, PakistanQ. 0. Navarro, Philippine Atomic Research Center, Quezon City,
Philippine IslandsJ. Kuzminski, Inst. of Physics, Katowice, PolandW. Zych, Inst. of Nuclear Research, Warsaw, PolandF. da Silva, Lab. de Fisica e Engenharia Nucleares, Sacavem, PortugalInstitute for Physics and Nuclear Eng., Bucharest, Romania
Timisoara, U. of, Library, RomaniaD. Branford, U. Edinburgh, ScotlandD. H. Pringle, Nuclear Enterprises Ltd., Edinburgh, ScotlandE. Barnard, Atomic Energy Board, Pretoria, South AfricaF. D. Brooks, U. Cape Town, South AfrcaW. R. McMurray, Southern Universities Nuclear Inst., Faure, South AfricaD. W. Mingay, Atomic Energy Board, Pretoria, South AfricaD. Reitmann, National Accelerator Center, Faure, South AfricaJ. P. F. Sellschop, U. of the Witwatersrand, South Africa0. Almen, Chalmers U. of Technology, Gothenburg, SwedenI. Bergstrom, Nobelinstitut for Fysik, Stockholm, SwedenM. Braun, Research Inst. of Physics, Stockholm, SwedenN. Ryde, Chalmers U. of Technology, Gothenburg, SwedenTandem Accelerator Lab., Uppsala, SwedenJ. Rafelski, CERN, Geneva, SwitzerlandS. Ketudat, Chulalongkorn U., Bangkok, ThailandDiyarbakir U., D. U. Fen Fakultesi, TurkeyA. Saplakoglu, Ankara Nuclear Research and Training Center, Ankara, TurkeyA. J. Kalnay, IVIC, Physics Section, Caracas, Venezuelavenezuela, Universidad Central de, Physics Dept., Caracas, Venezuela