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Isomers and shape transitions in the n-rich A~190 region:
the influence of angular momentum Phil Walker University of Surrey prolate K isomers vs. oblate collective rotation
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Segre chart with isomers
Z=72 (Hf) K isomers (A ~ ) This proposal is to study K isomers in deformed nuclei, extending the known A~180 region into the n-rich domain. We focus on hafnium isotopes, for which the Z=72 Fermi level is very favourably placed amongst high-K orbitals. adapted from Walker and Dracoulis, Nature 399 (1999) 35
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prolate-oblate shape transition
n-rich hafnium ground states critical point N = 116 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 next slide. Robledo et al., J. Phys. G: Nucl. Part. Phys. 36, (2009).
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[PRL43 (1979) 1979] Hilton and Mang oblate prolate HFB calculations
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180Hf oblate band? three 20+ states pre-Gammasphere
high-K yrast isomers: d'Alarcao et al., Phys. Rev. C59 (1999) 1227(R) three 20+ states Tandel et al., Phys. Rev. Lett. 101 (2008) with Gammasphere 3600
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cranked n-rich hafnium: 3 well-deformed minima
collective prolate ћω = 0.2 ћω = 0.3 ћω = 0.4 collective oblate non-collective prolate This cranking calculation shows an important role for angular momentum (approx 5, 15 and 25 units, going left to right). The well-deformed oblate shape is stabilised by reinforcing neutron and proton rotation alignments (low K), competing with prolate high-K isomers. We plan to study the high-K isomers in the ESR. 182Hf example: Xu, Walker and Wyss, Phys. Rev. C62 (2000)
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190Hf TRS 190Hf TRS oblate rotor prolate oblate I=32 ħω = 0 MeV
beyond the critical point oblate ħω = 0.3 MeV ħω = 0.45 MeV I=32 Xu et al., unpublished
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Hf prolate vs oblate 182Hf 186Hf oblate prolate oblate prolate mqp
[Xu et al., Phys. Rev. C62 (2000) ]
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Nilsson single-particle diagram N = 116 (188Hf, 190W, 192Os)
prolate oblate
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data for even-even A~190 nuclei
186Os ns 188Os ns 190Os m 192Os s Z=76 Z=74 Z=72 184W μs μs 186W 16+ >3ms μs 188W 190W 10- ~1ms ? 182Hf μs m 184Hf s 186Hf 188Hf new data new data critical point
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W-190 gammas 190W ~1 ms a critical point nucleus
delayed gamma rays from 208Pb fragmentation at 1 GeV per nucleon ~1 ms 190W a critical point nucleus
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isomer energies, potential energy surfaces
190W: prolate (keV) 2360±25 (exp) ground state PES ~1ms 2015 6s 1920 m 10- 10- (calc) 1700 1633 10- isomer PES 0+ 190Os Os W116 [Walker and Xu, PLB636 (2006) 286]
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190W with Gammasphere Lane et al., Phys. Rev. C82 (2010)
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190W with Gammasphere Lane et al., Phys. Rev. C82 (2010) 051304
10- isomer at 1839 keV
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isomer energies, potential energy surfaces
190W: prolate (keV) 2360±25 (exp) ground state PES ~1ms 2015 6s µs 1920 m 10- 10- (calc) 1700 1633 10- isomer PES 0+ 190Os Os W116 [Walker and Xu, PLB636 (2006) 286]
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190W with Gammasphere That was the high-K isomer. What about the
Lane et al., Phys. Rev. C82 (2010) That was the high-K isomer. What about the oblate rotation?
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190W with Gammasphere That was the high-K isomer. What about the
(12+) yrast at 2653 keV Lane et al., Phys. Rev. C82 (2010) That was the high-K isomer. What about the oblate rotation?
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190W TRS: prolate to oblate
rotation alignment of 2 i13/2 neutrons with oblate shape ħω = MeV ħω = MeV γ=0o I = 4 prolate I = 14 oblate γ=-60o [Walker and Xu, PLB636 (2006) 286]
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N=116 experimental energies, spins and half-lives 2653 (i 13/2)2 12+ ?
2451 2439 9 ns 190W Lane et al. 5 ns 194Pt and 196Hg: Levon et al., Nucl. Phys. A764 (2006) 24 192Os: Valiente-Dobon et al., Phys. Rev. C69 (2004) 412 329 2+ 207 206 0+ 74W Os Pt Hg
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projected shell model (angular momentum basis)
Sun et al., PLB659 (2008) 165
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summary oblate-prolate competition in N = 116 188Hf – 190W – 192Os
N = 116 seems to be the critical-point neutron number focus on angular momentum effects 10- prolate K isomers 12+ isomers: bandheads of collective oblate bands?? giant backbending candidates: cf. Hilton and Mang 1979 oblate rotation becomes yrast over a wide spin range more data needed!! (188Hf, 190W and/or 192Os)
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