University of Brighton 30 March 2004RISING stopped beam physics workshop Microsecond isomers in A~110 nuclei Few nuclei have oblate ground states (~86% are prolate in their ground state) Phys Rev C64 (2001) Fewer have oblate shapes which compete at ‘high’ angular momentum. Global shape calculations Nucl Phys A617 (1997) 282 suggest such states might exist in the neutron-rich A~110 nuclei but how to study them??

University of Brighton 30 March 2004RISING stopped beam physics workshop Location of oblate ground states in A~110. Skalski, Mizutori, Nazarewicz Nucl Phys A617 (1997) 282.

University of Brighton 30 March 2004RISING stopped beam physics workshop X(5) and tetrahedral shapes Tetrahedral Prolate

University of Brighton 30 March 2004RISING stopped beam physics workshop Oblate shapes remain at high spin TRS surfaces for 112 Zr top: h  0.1 MeV bottom: h  1.0 MeV (I~36) Xu, Walker et al., Phys Rev C65 (2002) R

University of Brighton 30 March 2004RISING stopped beam physics workshop Possible experimental handle ? Configuration-constrained calculations suggest prolate multi-quasiparticle configurations in these nuclei. Xu, Walker et al., Phys Rev C65 (2002) R e.g in 114 Zr prolate 2 quasi- neutron J  =K  =7 - state predicted at E ex =2.7 MeV

University of Brighton 30 March 2004RISING stopped beam physics workshop Location of the multi-qp states

University of Brighton 30 March 2004RISING stopped beam physics workshop 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. 110 Ru, J  =K  =5 -  = 65 0 state predicted at 1.4 MeV. Possible decay from the multi-qp state - ILL experiment on Lohengrin

University of Brighton 30 March 2004RISING stopped beam physics workshop Prolate multi-qp states predicted in the region of oblate high-spin states. In particular heavy A>110, Zirconium nuclei

University of Brighton 30 March 2004RISING stopped beam physics workshop The particular case of 114 Zr Ground state  2 = 0.17,  = 60 0 Prolate J  =K  =7 - state predicted at 2.7 MeV Assume E1 transition to J  =6 + state of gsb For 1 MeV E1, 1 W.u. corresponds to t 1/2 of ~ s 500 keV E1, 1 W.u. corresponds to t 1/2 of ~ s E1’s are typically retarded by 10 4 and transition has  K=7 => = 6, hindrance ~ Combining these 2 gives lifetime in the microsecond region.

University of Brighton 30 March 2004RISING stopped beam physics workshop What is currently known about neutron-rich zirconiums? 110 Zr Heaviest identified Projectile -fission 750.A MeV 238 U on Be 0.4 nb Bernas et al Phys Letts B415 (1997) 111.

University of Brighton 30 March 2004RISING stopped beam physics workshop Rate calculation for projectile-fission (calcs. indicate projectile fragmentation not suitable) Assume  = 0.4 nb, 10 8 particles per spill 9 Be target, 2 g/cm 2 => atoms/cm 2 => Zr per spill 3 spills per minute => ~ per minute Fraction in isomeric state =10 % Efficiency of RISING = 10 % Efficiency of FRS =10 %  ~ per day. 4,629 days for 100 counts!!

University of Brighton 30 March 2004RISING stopped beam physics workshop Comparison with something which we know works!! Zsolt’s experiment on 190 W (  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 particles per spill Is this realistic?