Microsecond isomers in A~110 nuclei

1. Microsecond isomers in A~110 nuclei • Few nuclei have oblate ground states (~86% are prolate in their ground state) Phys Rev C64 (2001) 037301. • Fewer have oblate shapes which compete at ‘high’ angular momentum. • Global shape calculations NuclPhys A617 (1997) 282 suggest such states might exist in the neutron-rich A~110 nuclei but how to study them?? RISING stopped beam physics workshop

2. Location of oblate ground states in A~110. Skalski, Mizutori, Nazarewicz Nucl Phys A617 (1997) 282. RISING stopped beam physics workshop

3. X(5) and tetrahedral shapes Tetrahedral Prolate RISING stopped beam physics workshop

4. Oblate shapes remain at high spin TRS surfaces for 112Zr top: hw = 0.1 MeV bottom: hw = 1.0 MeV (I~36) Xu, Walker et al., Phys Rev C65 (2002) 021303R RISING stopped beam physics workshop

5. Possible experimental handle ? • Configuration-constrained calculations suggest prolate multi-quasiparticle configurations in these nuclei. • Xu, Walker et al., Phys Rev C65 (2002) 021303R • e.g in 114Zr prolate 2 quasi-neutron Jp=Kp=7- state predicted at Eex=2.7 MeV RISING stopped beam physics workshop

6. Location of the multi-qp states RISING stopped beam physics workshop

7. Oblate qp isomers in the N=66 nuclei • N=66 nuclei predicted to have a prolate ground state and oblate multi-qp state at ~ 2.0 MeV. • e.g. 110Ru, Jp=Kp=5-g = 650 state predicted at 1.4 MeV. • Possible decay from the multi-qp state - ILL experiment on Lohengrin RISING stopped beam physics workshop

8. Prolate multi-qp states predicted in the region of oblate high-spin states. In particular heavy A>110, Zirconium nuclei RISING stopped beam physics workshop

9. The particular case of 114Zr Ground state b2 = 0.17, g = 600 Prolate Jp=Kp=7- state predicted at 2.7 MeV Assume E1 transition to Jp=6+ state of gsb For 1 MeV E1, 1 W.u. corresponds to t1/2 of ~ 3 10-16 s 500 keV E1, 1 W.u. corresponds to t1/2 of ~ 2 10-15 s E1’s are typically retarded by 104 and transition has DK=7 => n = 6, hindrance ~ 106. Combining these 2 gives lifetime in the microsecond region. RISING stopped beam physics workshop

10. What is currently known about neutron-rich zirconiums? 110Zr Heaviest identified Projectile -fission 750.A MeV 238U on Be 0.4 nb Bernas et al Phys Letts B415 (1997) 111. RISING stopped beam physics workshop

11. Rate calculation for projectile-fission(calcs. indicate projectile fragmentation not suitable) Assume s = 0.4 nb, 108 particles per spill 9Be target, 2 g/cm2 => 1.3 1023 atoms/cm2 => 5 10-3 Zr per spill 3 spills per minute => ~15 10-3 per minute Fraction in isomeric state =10 % Efficiency of RISING = 10 % Efficiency of FRS =10 % • ~21 10-3 per day. 4,629 days for 100 counts!! RISING stopped beam physics workshop

12. Comparison with something which we know works!! • Zsolt’s experiment on 190W (s estimated = 2500 nb) => need to find a factor of 2500/0.4 =6,250 • Assume FRS efficiency is constant • RISING gives an improvement of a factor of 10 over the set-up used for Zsolt’s experiment. • Need a factor of 625 in beam intensity, i.e need 6.25 1010 particles per spill • Is this realistic? RISING stopped beam physics workshop