Recent Nuclear Structure and Reaction Dynamics Studies Using Mutlinucleon Transfer Reactions

Paddy Regan

Dept. of Physics

University of Surrey,UK

E-mail: p.regan@surrey.ac.uk

Laser Physics Letters 1 (2004) 317-324

Outline of Talk

• Thin target multinucleon transfer reactions:– 100Mo+136Xe : alignments, E-GOS plots and some reaction

mechanism info.– 198Pt+136Xe: 136Ba I=10+seniority isomers, effective charges and

some reaction mechanisms– 184W K-isomers and –4p transfer

• Future Aims/ Plans.– 170Dy (ish)– N=50 (ish)

Main physics interest in neutron-rich nuclei is based on the EVOLUTION OF SHELL STRUCTURE and the appearance of

‘large gaps in the nuclear single-particle spectrum’.

Reasons to study neutron-rich nuclei

1) Evolution of collective modes (vibrations, rotations, superdef ?) from spherical states by altering (N,Z,I, Ex).

2) Identification of specific nucleonic orbitals, e.g. via isomeric decays, g-factors, B(E2:I->I-2), effective charges, shell model descriptions, seniority schemes, deformed (Nilsson) schemes etc.

3) Identifying new nuclear ‘exotica’, e.g., the unexpected, beta-decaying high-spin states, new symmetries (e.g., 32), neutron ‘skins’, new shell closures, shape changes etc.

2)12( LModified from Introductory Nuclear Physics, Hodgson, Gadioli and Gadioli Erba, Oxford Press (2000) p509

Aim? To perform high-spin physics in stable and neutron rich nuclei. Problem: Fusion makes proton-rich nuclei.Solutions? (a)fragmentation (b) binary collisions/multi-nucleon transfer

See eg. Broda et al. Phys. Rev Lett. 74 (1995) p868Juutinen et al. Phys. Lett. 386B (1996) p80Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23Krolas et al. Acta. Phys. Pol. B27 (1996) p493Asztalos et al. Phys. Rev. C60 (1999) 044307

CCMMAX

MAX

TB

TLF

VER

L

LAA

L

2

2

31

2

1

1

7

2

:limit Rolling

-1

cos-1

by calculated then is correctionDoppler The

coscoscoscossinsinsinsin)cos(

where

)cos(r.r

by given is angleray -fragment/ the

k )cos( , j )sin()sin( ,i )cos()sin(

k, and j i, rsunit vectoCartesian For

2

2,1'

2121212112

122121

1,2

1,2

EE

rr

rzryrx

z

x

y

Simon et al., Nucl. Inst. Meth. A452, 205 (2000)

BLF

TLF

beam tlftlf

blfblf

Ge

TOF ~5-10 ns.ns-s isomers can de-excite in bestopped by CHICO position detector. Delayeds can still be viewedby GAMMASPHERE.

Rochester Group

100Mo + 136Xe @ 700 MeV GAMMASPHERE + CHICOPHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Can see clearly to spins of 20ħ using thin-target technique.

Can we use the data from the CHICO+Gammasphere expt. to understand the ‘DIC’ reaction mechanism ? A wide range of spins & nuclei are observed.

Crossing and alignments well reproduced by CSM, although AHVs

24

24

2 :Rotor

0 : Vibrator

)2(

242

),1(2

:Rotor

,2

:Vibrator

22

22

J

J

J

n

JR

JR

J

JJER

JEJJE

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nE

PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502

E-GOS plot appears to indicate that Vibrator-Rotator phase change is a feature of near stable (green) A~100 nuclei.

BUT….what is the microscopic basis ?

‘Rotational alignment’ can be a crossing between quasi-vibrational GSB & deformed rotational sequence.(stiffening of potential by population of high-j, equatorial (h11/2) orbitals).

PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502

50

82

[550]1/2-

1h11/2

1g9/2

[541]3/2-

What about odd-A nuclei….are the h11/2 bands ‘rotational’ ?

See PHR, Yamamoto, Beausang, Zamfir, Casten, Zhang et al., AIP Conf. Proc. 656 (2002) p422

‘Weak Coupling’

E/(I-j) E-GOS extension for odd-A

Suggests 11/2- band is anharmonic, -soft rotor?

BUT seems to work ok for +ve parity bandsvib ->rotor following(h11/2)2 crossing.

case. 0 even)-(even for the toreduces which

22

2

24 by, simplified becan This

24

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jI

jRER

RKIRjI

jjIE

jIRjI

jE

jI

jI

I

I

I

EIR

jGOSE

j

jII

Carl Wheldon (HMI-Berlin) has suggested extension of E-GOS by ‘renormalising’ the rotational energies at the bandhead.

If the band-head spin of a sequence is given by j then substituting Ij in place of I, one obtains,

seems to work ok, h11/2 bands now look like rotors,

Even-Even yrast sequences and odd-A +ve parity only show rotational behaviour after (h11/2 )2 crossing….

R.Broda et al., Phys. Rev. C49 (1994)

0

10

20

30

40

50

%>Ecoul

Ltlf (roll)

v/c graz tlf

Linear(%>Ecoul)

0

10

20

30

40

50

60

620 648 677 705 733 761 790E_beam (MeV)

blf_graz

tlf_graz

lmax/10

Kinematics and angular mom. input calcs (assumes ‘rolling mode’) for 136Xe beam on 100Mo target.

Estimate ~ 25hbar in TLFfor ~25% above Coul. barrier. For Eb(136Xe)~750 MeV, in labblf~30o and tlf~50o.

100Mo +136Xe (beam) DIC calcs.

+2p

-2n

+2n

Fold distributions highlight different reaction mechanisms

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Wilczynski (‘Q-value loss) Plot A.D.Yamamoto, Surrey PhD thesis (2004)

Emission angle of TLFs can give information/selection on reaction mechanism (and maybe spins input ?)

TLFs

BLFs

elastics

PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

Gating on anglegives a dramatic channel selection in terms of population.

Relative Intensitiesof 6+->4+ yrast transitions in TLFs (relative to 100Mo) for 136Xe beam on 100Mo target at GAMMASPHERE+ CHICO.

198Pt +136Xe, 850 MeV

J.J. Valiente-Dobon, PHR,C.Wheldon et al., Phys. Rev.C69 (2004) 024316

67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

59585756555453525150

757473

76

8483828180797877

N/Z compound

nano and microsecond isomerson gated 198Pt+136Xe withGAMMASPHERE+CHICODIC 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124

J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313136Xe+198Pt reaction beam-like fragment isomers.

131I

133I

128Te

130Te 136Xe

132Xe

138Ba

137La

136Xe+198Pt Target-like fragment isomers

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313

184W

185Re

191Os

192Os

195Os

192Pt

198Pt

193Au

PHR, Valiente-Dobon, Wheldon et al., Laser Phys Letts. 1 (2004) 317

Can see 184-194Os in binary partner channels. i.e.in 2p transfer, up to 14 neutrons evaporated. ( 4n -> 194Os is heaviest known).

198Pt, 2+

136Xe, 2+

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313

138Ce 125Sb

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) 024313

Identification of new ‘seniority’ isomer in 136Ba, N=80 isotone.

J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) 024316

T1/2=91(2) ns

N=80 isotonic chain, 10+ isomers, (h11/2)-2I=10+

Q. Why does Ex(10+) increase while E(2+) decreases ? 91(2) ns

Structure of 8+ final state changes from 134Xe -> 136Ba ?See Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) 024313

Isomer decayalso depends on structureof final state

N=80, (h11/2)-210+ isomers

Energy of N=80 I=10+ isomers correlates with energy increaseof 11/2- singleneutron in N=81 isotones.

Increase in 10+ energy, plusexpansion of proton valencespace means8+ yrast state now (mostly)NOT (h11/2)-2

for Z>54

N=81

N=80

Ex, I=11/2 -

Ex, I=10

Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) 024313

Pair Truncated Shell Model

Calculations (by Yoshinaga,Higashiyama et al. Saitama)predict yrast 8+ in 136Ba no longer mostly (h11/2)-2

but rather, (d5/2)2(g7/2)2

0.000

0.963

2.760

g7/2

d5/2

h11/2 Protons, max. seniority 2spin = 6 ħ (from (g7/2)2.

Seniority 4 states though can have up to7/2 + 5/2 + 5/2 +3/2 = 10 ħ

Expect neutron ‘seniority scheme’for (h11/2)-2 ‘j2’ mutlipletconfiguration at N=80 (e.g. 130Sn).

132Te, 134Xe have proton excitationsdue to g7/2, d5/2 at 0+,2+,4+,6+ but not competing 8ħ and 10ħ states.

Extra collectivity for higher-Z pushes down 0+ and 2+.

Proton s.p. energiesused in 136Ba SM calcs

Search for long (>100ms) K-isomers in neutron-rich(ish) A~180 nuclei.

low-K high-K mid-K j

K

:rule sel. -K

Walker and Dracoulis Nature 399 (1999) p35

(Stable beam) fusion limit makes high-K in neutronrich hard to synthesise

also a good number for K-isomers.

170Dy, double mid-shell, ‘purest’ K-isomer ? (see PHR, Oi, Walker, Stevenson and Rath, Phys. Rev. C65 (2002) 037302)

Max at 170Dy

K=6+state favoured

,

1

21

exp

21

WT

Tf

Best K-isomer?Doubly-mid-shell nucleus, 170DyN=104, Z=66 (Np.Nn=352=Maximum!).Appears to be a correlation betweenf values and NpNn for K=6+ isomers in A~180 region.(see PHR, Oi, Walker, Stevenson & Rath, Phys. Rev. C65 (2002) 037302)

Extrapolation suggestsisomer in 170Dy lives forhours….could be beta-decay candidate.

172Hf, 174Yb, 174Hf, 176Hf, 178Hf, 178W K=6+ isomers

170Dy ?

N=104 isotones, K=6+ energy

Try at PRISMA in 2005

International ConferenceOn NUclear STructure, Astrophysics & Reactions University of Surrey, Guildford, UK5-8 January 2005Payment deadline last Friday (1st October)

http://www.ph.surrey.ac.uk/cnrp/nustar05