30 March 2004 RISING stopped beam physics workshop University of Brighton

 

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 Nucl Phys A617 (1997) 282 suggest such states might exist in the neutron-rich A~110 nuclei but how to study them??

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

Location of oblate ground states in A~110.

Skalski, Mizutori, Nazarewicz Nucl Phys A617 (1997) 282.

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

X(5) and tetrahedral shapes

Tetrahedral

Prolate

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

Oblate shapes remain at high spin

TRS surfaces for 112Zr

top: h0.1 MeV

bottom: h1.0 MeV (I~36)

Xu, Walker et al., Phys Rev C65 (2002) 021303R

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

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 J=K=7- state predicted at Eex=2.7 MeV

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

Location of the multi-qp states

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

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, J=K=5- = 650 state predicted at 1.4 MeV.

•Possible decay from the multi-qp state - ILL experiment on Lohengrin

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

Prolate multi-qp states predicted in the region of oblate high-spin states.

In particular heavy A>110, Zirconium nuclei

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

The particular case of 114Zr

Ground state 2 = 0.17, = 600

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 t1/2 of ~ 3 10-16 s500 keV E1, 1 W.u. corresponds to t1/2 of ~ 2 10-15 s

E1’s are typically retarded by 104 and transition has K=7 => = 6, hindrance ~ 106. Combining these 2 gives lifetime in the microsecond region.

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

What is currently known about neutron-rich zirconiums?

110Zr Heaviest identifiedProjectile -fission750.A MeV 238U on Be0.4 nb Bernas et al Phys Letts B415 (1997) 111.

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

Rate calculation for projectile-fission(calcs. indicate projectile fragmentation not suitable)

Assume = 0.4 nb, 108 particles per spill9Be 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!!

30 March 2004 RISING stopped beam physics workshop University of Brighton

 

Comparison with something which we know works!!

• Zsolt’s experiment on 190W ( 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 10over 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?