Isomers and shape transitionsin the n-rich A~190 region:

Phil WalkerUniversity of Surrey

prolate K isomers vs.oblate collective rotation

the influence of angular momentum

Segre chart with isomers

adapted from Walker and Dracoulis, Nature 399 (1999) 35

K isomers(A ~ 170-190)

Z=72 (Hf)

prolate-oblate shape transition

Robledo et al., J. Phys. G: Nucl. Part. Phys. 36, 115104 (2009).

0

n-rich hafnium ground states

60

γ

30

N = 116critical point

Hilton and Mang

[PRL43 (1979) 1979]

prolate

oblate

HFB calculations

180Hf oblate band?

Tandel et al.,Phys. Rev. Lett. 101(2008) 182503with Gammasphere

three 20+ statespre-Gammaspherehigh-K yrast isomers:d'Alarcao et al.,Phys. Rev. C59(1999) 1227(R)

3600

cranked n-rich hafnium: 3 well-deformed minima

collective prolate

non-collective prolate

182Hf example: Xu, Walker and Wyss, Phys. Rev. C62 (2000) 014301

ћω = 0.2 ћω = 0.3 ћω = 0.4

collective oblate

190Hf TRS 190Hf TRSoblate rotor

ħω = 0 MeV ħω = 0.15 MeV

ħω = 0.3 MeV ħω = 0.45 MeV

prolate

oblate

I=32

Xu et al., unpublished

beyond the critical point

Hf prolate vs oblate182Hf186Hf

prolate

oblate

mqpprolate

[Xu et al., Phys. Rev. C62 (2000) 014301]

prolateoblate

Nilsson single-particle diagram N = 116 (188Hf, 190W, 192Os)

oblate prolate

data for even-even A~190 nuclei

190W

10- ~1ms

192Os

10- 6s

186W16+ >3ms

7- 20μs

190Os

10- 10m

188W

182Hf13+ 40μs

8- 62m

184Hf

8- 48s

184W15 0.2μs

5- 8μs

188Os

7- 14ns

186Os

7- 8ns

Z=76

Z=74

Z=72

N = 110 112 114 116

?

188Hf 186Hf

new data new data

critical point

W-190 gammas

190W

delayed gamma rays from 208Pb fragmentation at 1 GeV per nucleon

~1 ms

a critical point nucleus

isomer energies, potential energy surfaces

190Os114 192Os116 190W116

(calc)

(exp)

0+

10-

1633

2360±25

2015 6s

19201705 10m

1700

~1ms

190W: prolate

10- isomer PES

ground state PES

10-

(keV)

[Walker and Xu, PLB636 (2006) 286]

190W with Gammasphere

Lane et al.,Phys. Rev. C82(2010) 051304

190W with Gammasphere

Lane et al.,Phys. Rev. C82(2010) 051304

10- isomer at 1839 keV

isomer energies, potential energy surfaces

190Os114 192Os116 190W116

(calc)

(exp)

0+

10-

1633

2360±25

2015 6s

19201705 10m

1700

~1ms

190W: prolate

10- isomer PES

ground state PES

10-

(keV)

1839 240µs

[Walker and Xu, PLB636 (2006) 286]

190W with Gammasphere

Lane et al.,Phys. Rev. C82(2010) 051304

That was thehigh-K isomer.What about the oblate rotation?

190W with Gammasphere

Lane et al.,Phys. Rev. C82(2010) 051304

That was thehigh-K isomer.What about the oblate rotation?

(12+) yrast at 2653 keV

190W TRS: prolate to oblate

ħω = 0.216 MeVħω = 0.200 MeV

I = 4prolate

I = 14oblate

rotation alignment of 2 i13/2 neutrons with oblate shape

γ=0o

γ=-60o

[Walker and Xu, PLB636 (2006) 286]

N=116

74W 76Os 78Pt 80Hg0+

2+

(i 13/2)2

12+

2653

207 206

2451

412

2439

329

9 ns 5 ns

?200 ns

194 P

t and

196 H

g: L

evon

et a

l., N

ucl.

Phy

s. A

764

(200

6) 2

4

experimental energies, spins and half-lives

190W Lane et al.

192 O

s: V

alie

nte-

Dob

on e

t al.,

Phy

s. R

ev. C

69 (

2004

) 02

4316

projected shell model(angular momentum basis)

Sun et al., PLB659 (2008) 165

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)