1. Properties of neutron-rich hafnium high-spin isomers: P-325
P.M. Walker1,2, P.H. Regan1, Z. Podolyak1, M.W. Reed1, R.T. Wood1,
M. Kowalska2, K.T. Flanagan3, J. Billowes3, B. Cheal3, D.H. Forest4,
G. Tungate4, G. Neyens5, M.L. Bissell5, U. Köster6, Y. Litvinov7,
C. Kozhuharov7, B. Blank8, P. Delahaye9, G.D. Dracoulis10
1 University of Surrey, UK
2 CERN, Geneva, Switzerland
3 University of Manchester, UK
4 University of Birmingham, UK
5 University of Leuven, Belgium
6 ILL, Grenoble, France
7 GSI, Darmstadt, Germany
8 CENBG, Bordeaux, France
9 GANIL, Caen, France
10ANU, Canberra, Australia

2. physics motivation Upper part of shell (N=82-126, Z=50-82).
Reinforcing proton and neutron effects.
Prolate-to-oblate phase transition (I=0).
Prolate “deformation-aligned” high-K states vs. oblate rotation-aligned (I=10-20).
Access gained through isomer decays.
Isomer half-lives reflect underlying physics (e.g. level-density effect on K mixing).

3. prolate-oblate shape transition
n-rich hafnium ground states
HFB + SLy4 60 γ 30
Here calculated ground-state shapes are shown (part of a much wider range of calculated shapes). The delicate balance in 188Hf between prolate and oblate shapes is evident. It is important also to consider the effects of angular momentum – see later slide.
Robledo et al., J. Phys. G: Nucl. Part. Phys. 36, (2009).

4. Nilsson single-particle diagram N = 116 Fermi level (188Hf)
Here we illustrate the prolate (high-K) and oblate (low-K) Fermi levels for neutrons. The situation is similar for protons, though in a different shell. The proton and neutron shells are each 2/3 filled.
prolate
oblate

5. Nilsson single-particle diagram N = 116 Fermi level (188Hf)
and similarly for protons
Here we illustrate the prolate (high-K) and oblate (low-K) Fermi levels for neutrons. The situation is similar for protons, though in a different shell. The proton and neutron shells are each 2/3 filled.
prolate
oblate

6. prolate-oblate shape transition
182Hf
186Hf
oblate rotation
prolate rotation
prolate K states
configuration constrained TRS calculations
Xu, Walker and Wyss, Phys. Rev. C62 (2000)

7. Nuclear chart with isomers
Z=72 (Hf)
A~190
[Walker and Dracoulis, Nature 399 (1999) 35, updated]

8. hafnium (Z=72) 4-quasiparticle isomers
178Hf Hf
expt.
calc.
predictions
Walker and Dracoulis, Nature 399 (1999) 35; Hyp. Int. 135 (2001) 83

9. hafnium (Z=72) 4-quasiparticle isomers
178Hf Hf
expt.
calc. X
(15)
12m
Reed et al. 2010
184Hf
predictions
Walker and Dracoulis, Nature 399 (1999) 35; Hyp. Int. 135 (2001) 83

10. isomers in the storage ring at GSI
10-second snapshots
197Au fragmentation
A = 184, q = 72+
0e 1e
m g Ta
bare Hf
2.5 MeV
time (minutes) 10
2.5 MeV
A = 184, q = 72+ 20
frequency
Reed et al., Phys. Rev. Lett. 105 (2010)

11. 197Au fragmentation at GSI
beam
We used a 197Au beam, and found new, long-lived isomers in 186Ta, 187Ta, 183Hf, 184Hf and (tentatively) in 186Hf.
new
isomers
T1/2 >10 s
Reed et al., Phys. Rev. Lett. 105 (2010)

12. W and Ir spallation at ISOLDE
this proposal
target nuclides
isomers
to study

13. IS-537 experiment => isomer half-lives β decays γ decays
184Hf shifts
183Hf shifts
setting up shifts
Total beam time: 9 shifts
ISOLDE tape transport
ion beam
=> isomer half-lives
β decays
γ decays Ge Ge
β-γ-γ coincidences

14. 184Hf isomer data decay Eγ-spec EESR T1/2(exp) ground state (0+) β 4 h
isomer 1 (8-) γ+β (1)a 1264(10) 48 s
isomer 2 (15+) β (10) 12 min
a Krumbholz et al., Z. Phys. A351 (1995) 11
keV
keV
new data
Reed et al.
PRL105 (2010)
172501
Hf 4-quasiparticle isomers
new calculations
Liu et al.
Phys. Rev. C83
(2011)