Recent Nuclear Structure and Reaction Dynamics Studies Using Mutlinucleon Transfer Reactions Paddy Regan Dept. of Physics University of Surrey,UK E-mail:

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Recent Nuclear Structure and Reaction Dynamics Studies Using Mutlinucleon Transfer Reactions Paddy Regan Dept. of Physics University of Surrey,UK

Laser Physics Letters 1 (2004)

Outline of Talk Thin target multinucleon transfer reactions: – 100 Mo+ 136 Xe : alignments, E-GOS plots and some reaction mechanism info. – 198 Pt+ 136 Xe: 136 Ba I  =10 + seniority isomers, effective charges and some reaction mechanisms – 184 W K-isomers and –4p transfer Future Aims/ Plans. – 170 Dy (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 , E x ). 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.

Modified 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) p868 Juutinen et al. Phys. Lett. 386B (1996) p80 Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23 Krolas et al. Acta. Phys. Pol. B27 (1996) p493 Asztalos et al. Phys. Rev. C60 (1999)

z x y    

Simon et al., Nucl. Inst. Meth. A452, 205 (2000) BLF TLF beam  tlf  tlf  blf  blf Ge TOF ~5-10 ns. ns-  s isomers can de-excite in be stopped by CHICO position detector. Delayed  s can still be viewed by GAMMASPHERE. Rochester Group

100 Mo MeV GAMMASPHERE + CHICO PHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329

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

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

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 (h 11/2 ) orbitals). PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003)

50 82 [550]1/2 - 1h 11/2 1g 9/2 [541]3/2 -

What about odd-A nuclei….are the h 11/2 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 bands vib ->rotor following ( h 11/2 ) 2 crossing.

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 I  j in place of I, one obtains,

 seems to work ok, h 11/2 bands now look like rotors, Even-Even yrast sequences and odd-A +ve parity only show rotational behaviour after ( h 11/2 ) 2 crossing….

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

Kinematics and angular mom. input calcs (assumes ‘rolling mode’) for 136 Xe beam on 100 Mo target. Estimate ~ 25hbar in TLF for ~25% above Coul. barrier. For E b ( 136 Xe)~750 MeV, in lab  blf ~30 o and  tlf ~50 o. 100 Mo Xe (beam) DIC calcs.

+2p -2n +2n Fold distributions highlight different reaction mechanisms PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003)

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)

Gating on angle gives a dramatic channel selection in terms of population. Relative Intensities of 6 + ->4 + yrast transitions in TLFs (relative to 100 Mo) for 136 Xe beam on 100 Mo target at GAMMASPHERE + CHICO.

198 Pt Xe, 850 MeV J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004)

N/Z compound nano and microsecond isomers on gated 198 Pt+ 136 Xe with GAMMASPHERE+CHICO DIC J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004)

J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) Xe+ 198 Pt reaction beam-like fragment isomers. 131 I 133 I 128 Te 130 Te 136 Xe 132 Xe 138 Ba 137 La

136 Xe+ 198 Pt Target-like fragment isomers J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004) W 185 Re 191 Os 192 Os 195 Os 192 Pt 198 Pt 193 Au

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

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

198 Pt, Xe, 2 + J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004)

138 Ce 125 Sb J.J.Valiente-Dobon, PHR, C.Wheldon et al., PRC69 (2004)

Identification of new ‘seniority’ isomer in 136 Ba, N=80 isotone. J.J. Valiente-Dobon, PHR, C.Wheldon et al., Phys. Rev. C69 (2004) T 1/2 =91(2) ns

N=80 isotonic chain, 10 + isomers, ( h 11/2 ) -2 I=10 + Q. Why does E x (10 + ) increase while E(2 + ) decreases ? 91(2) ns

Structure of 8 + final state changes from 134 Xe -> 136 Ba ? See Valiente-Dobon, PHR, Wheldon et al., PRC69 (2004) Isomer decay also depends on structure of final state N=80, ( h 11/2 ) isomers

Energy of N=80 I  =10 + isomers correlates with energy increase of 11/2 - single neutron in N=81 isotones. Increase in 10 + energy, plus expansion of proton valence space means 8 + yrast state now (mostly) NOT ( h 11/2 ) -2 for Z>54 N=81 N=80 E x, I  =11/2 - E x, I  =10

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

Pair Truncated Shell Model Calculations (by Yoshinaga, Higashiyama et al. Saitama) predict yrast 8 + in 136 Ba no longer mostly ( h 11/2 ) -2 but rather, (  d 5/2 ) 2 (  g 7/2 ) 2

g 7/2 d 5/2 h 11/2 Protons, max. seniority 2 spin = 6 ħ (from (  g 7/2 ) 2. Seniority 4 states though can have up to 7/2 + 5/2 + 5/2 +3/2 = 10 ħ Expect neutron ‘seniority scheme’ for ( h 11/2 ) -2 ‘j 2 ’ mutliplet configuration at N=80 (e.g. 130 Sn). 132 Te, 134 Xe have proton excitations due to g 7/2, d 5/2 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. energies used in 136 Ba SM calcs

Search for long (>100ms) K-isomers in neutron-rich(ish) A~180 nuclei. low-K high-K mid-K j K Walker and Dracoulis Nature 399 (1999) p35 (Stable beam) fusion limit makes high-K in neutron rich hard to synthesise  also a good number for K-isomers.

170 Dy, double mid-shell, ‘purest’ K-isomer ? (see PHR, Oi, Walker, Stevenson and Rath, Phys. Rev. C65 (2002) ) Max at 170 Dy K  =6 + state favoured

Best K-isomer? Doubly-mid-shell nucleus, 170 Dy N=104, Z=66 (N p.N n =352=Maximum!). Appears to be a correlation between f values and N p N n for K=6 + isomers in A~180 region. (see PHR, Oi, Walker, Stevenson & Rath, Phys. Rev. C65 (2002) ) Extrapolation suggests isomer in 170 Dy lives for hours….could be beta-decay candidate. 172 Hf, 174 Yb, 174 Hf, 176 Hf, 178 Hf, 178 W K=6 + isomers 170 Dy ? N=104 isotones, K=6 + energy Try at PRISMA in 2005

International Conference On NUclear STructure, Astrophysics & Reactions University of Surrey, Guildford, UK 5-8 January 2005 Payment deadline last Friday (1 st October)