New Isomers from Fast Fragmentation Reactions

Dr. Paddy Regan

Dept. of Physics

University of Surrey,

Guildford, GU2 7XH, UK

p.regan@surrey.ac.uk

primary beamPb @ 1GeV/u

Production target

Central focus, S2Final focus, S4

E(Z2)cu

eB

Q

A

FTO

catcher

degraderdegrader

dipole, B

scintscint

MW=x,y

scint(veto)

Use FRS (or LISE3) to ID exotic nuclei. Transport some in isomeric states (TOF~ x00ns).Stop and correlate isomeric decays with nuclei id.

eg. R. Grzywacz et al. Phys. Rev. C55 (1997) p1126 -> LISE C.Chandler et al. Phys. Rev. C61 (2000) 044309 ->LISE M. Pfutzner et al. Phys. Lett. B444 (1998) p32 -> FRS

Chandler et al. Phys. Rev. C61 (2000) 044309

67Ge

69Se

76Rb

Heaviest odd-odd,N=Z gammas, isobaric analog states ? 86Tc, C. Chandler et al. Phys. Rev. C61 (2000) 044309

8+ isomer in 78Zn, real evidence of 78Ni shell closure.J.M.Daugas et al. Phys. Lett.

B476 (2000) p213

136Sb

135Te

Use FRS to select projectile fission products (forward boosted ones). Note transmission a few %.

T1/2=565(50) ns state in 136Sb (Z=51, N=85)

M. Mineva et al. Eur. Phys. J. A11 (2001) p9-13

Gamma-gamma analysis on 200Pt isomer (21 ns!), Caamano et al. Nucl. Phys. A682 (2001) p223c; Acta Phys. Pol. B32 (2001) p763

33 ns isomer in 195Os (last stable 192Os), useful test of structure in prolate/oblate shape coexistence region. 194Os Wheldon et al. Phys. Rev. C63 (2001) 011304(R)

First id of ‘doubly mid-shell’ nucleus, 170Dy (N=104, Z=66). K=6+ isomers predicted for well deformed N=104 nuclei. TRS calcs (F.Xu) predict a very ‘stiff’, highly deformed prolate nucleus. Could be the best K-isomer?

Data from M.Caamano et al.

C. Schlegel et al.Physica Scripta T88 (2000) p72

High spins (>35/2) populated

Proton drip line isomer physicsfrom 208Pb fragmentation.N=74 chain of K=8- isomers.Next in chain would be 140Dy, proton decay daughter of (deformed) 141Tb.

Isomers orginally seen in fusion-evap (ANU data)A.M.Bruce et al. Phys.Rev. C50 (1994) p480and C55 (1997) p620

2

3/22

22

2

)1(exp

ratio,isomer predicts model off-cut sharp

1

3

3

210178.0

, 2

)1(exp

2

12

fJ jth

p

ppf

ffjj

JJdJPR

A

AAAA

JJJP

m

M. de Jong et al. Nucl. Phys. A613 (1997) p435

M. Pfutzner et al. Phys. Rev. C & Acta. Phys. Pol. (submitted)

iitot

i

fii

qq

effimp

tot

b

ttG

TOFTOF

FGbN

NR

1

expexp

11

expF

, )1(

0

2

2

22

1

11

Isomeric Ratio Calculations

M. Pfutzner et al. Acta. Phys. Pol. & Phys. Rev. C, (submitted)

M. Pfutzner et al. submitted to Phys Rev. C

Prompt flash knocks out a large portion of the detectors….effectively reduces the gamma efficiency by upto 80%! Need digital electronics and time stamping

The problem

Single ion selected by the fragment separator

time

coun

ts

0

plastic

Ge detector

trigger,time start

prompt isomer decay room background

thick Al stopper

Energy 100 MeV/uR 60 mg/cm2 Al

Probability to detect prompt radiation is large.

In a standard set-up only the first gamma is recorded.

DGF detection scheme

A1 A2 A3 A4

Ionization chamberL2

R4R2

L4Plastic scintillators

FRSsecond stage

Energy loss, DE

Beam

Position x2 - TAC(L2-R2) -

Position x4 - TAC(L4-R4) -

TAC(L2-L4) - TAC(R2-R4) -

TOF -

Gate logic

P a r t i c l e i d e n t i f i c a t i o n

DGF 1, 2

Clover detectors

Gamma energy, EG

Gate logic

D e c a y s p e c t r o s c o p y

DGF 3, 4, 5

Beam macrostructure

time [s]

Storing datain memory buffers

Readout

time [s]

microstructure

100 s

Gate

Ions

Gammas

M.Pfutzner,M.Hellstrom et al.

Pfutzner, Hellstrom, Mineva et al.

Other ways to get around the gamma-flash problem?

Segmented germanium detectors and digital electronicsfor each individual segment.

EURYSIS 6 x 6 germanium, Surrey/Liverpool/Darebury UK Gamma-Ray Tracking Project.

g-factors from fragmentation isomers

Basic idea, put isomer in B-field. Perturbation of gamma-ray angular distribution depends on induced Torque.

Rate of precession gives Larmor frequency, which gives g-factor.

‘Wiggles’ in count ratio between different angles from 13/2+ isomer, T1/2= 354(2)ns in 69Cu.

Neyens, Georgiev et al. RNB5 conference, in press,. Nucl. Phys. A

BaF2 ‘fast timing’ data from H. Mach et al. Contribution to ENAM 2001

Allows an ordering of the gammas under isomer from their (~ps) lifetimes.

J. Garces Narro et al. Phys Rev. C63 (2001) 044307

Implant fragments into Si strip detector…if N=Z, stop beam for 1second and wait…..

BIL gatedAll

T=1 ground states in heavy odd-odd N=Z

Summary and Forward Look• New nuclear structure

– along N=Z line (86Tc, Chandler et al.)

– around 78Ni (78Zn, Daugas et al.)

– from fission fragments (136Sb, Mineva, Hellstroem et al.)

– ‘terra incognita’ 190W, 195Os, 200,201,202Pt…170Dy? (Podolyak, Caamano et al.)

• Reaction information

– Isomeric ratios give estimate of spin input, imply useful tool for high-spin physics (Pfutzner et al).

• Developments in Techniques

– Digital electronics for gamma-flash (eg. 136Sb)

– Gamma-tracking with segmented detectors (Pearson, Dobon et al.)

– Fast timing to order gamma-rays in cascade (BaF2 Mach et a.)

– g-factors using TPAD method (Neyens, Georgiev et al.)

– Active stoppers for electron conversion (72,74Kr etc. Becker et al.) and beta, alpha, proton decays tags (GREAT).

• All in the RISING project@GSI.