1. Shape-coexistence enhanced by multi-quasiparticle excitations in A~190 mass region石跃
北京大学
导师：许甫荣教授

2. Outline
Introduction
The model
Calculation and discussion
Conclusion

3. Shape-coexistence in Pb isotopes with N~104
introduction
Shape-coexistence in Pb isotopes with N~104
prolate
oblate
prolate
oblate
G. D. Dracoulis et al.
Phys. Rev. C 67(2003)051301(R)
J. Pakarinen et al.
Phys. Rev. C 72(2005)011304(R)
186Pb
188Pb

4. Realistic calculation show soft and shallow PES
introduction
Realistic calculation show soft and shallow PES
R. Bengtsson, W. Nazarewicz, ZPA 334 (1989) 269

5. Shape mixing is especially pronounced for
light Po isotopes
introduction
It is the mixing
that complicates the shape idetification
of low spin band structures in light Po isotopes.
190Po
190Po
F. R. May et al., PLB 68 (1976) 113
Energy difference between
Neighbouring Countors is 100 keV!!

6. Two or three level mixing analysis
introduction
Two or three level mixing analysis

7. introduction 188Pb M. Bender et al. Phys. Rev. C 69(2004)064303
V. Hellemans et al.
Phys. Rev. C 77(2008)064324

8. introduction
Two mechanisms to stabilize different subminima in potential-energy surface
Collective rotation
Broken-pair excitation
The minima with larger deformations
are progressively favoured with increasing
angular momentum (large MOI).
possible K isomerism!!

9. Possibilities of K isomerism
introduction
Possibilities of K isomerism
The formation of high-K states can enhance the stability of different subminima through increasing the potential barriers between them.
The filling of strongly deformed-driving orbitals of the unpaired nucleons can polarize the soft nucleus to a larger deformation.
The above two ingredients, combined with a low Ex of high-K state, provide good conditions for the formation of K isomers.
Decays from isomeric states give valuable structure information.
Isomerism is a key feature in giving access to observables required for shape measurements.
motivation

10. Oblate shape motivation Oblate shape is very rare.
introduction
Oblate shape
Oblate shape is very rare.
The rareness of oblate deformation compared to prolate shape may be related to the detailed form of mean-field.
The study of oblate deformed K-isomers give insights into oblate single-particle levels.
motivation

11. 3.Adiabatic blocking: PLB435(1998)257.
model
1.Single particle energy: Woods-Saxon potential with universal parameter.
2.Paring interaction: Lipken-Nogami treatment of paring with its strength determined by average pairing gap method.
3.Adiabatic blocking: PLB435(1998)257.

12. Systematic calculations has been performed at
both oblate and prolate deformations
a) For oblate deformation
Pb, Po isotopes with N=104~114.
b) On prolate side
N=102,104 isotones with Z=74~82.

14. calculation

15. calculation

16. calculation
prolate

17. Shape transition!! Pb,Po isotopes discussion
M. Ionescu-Bujor, et al. PLB 650 (2007) 141

18. discussion
While almost all the ground states of the calculated nuclei have relatively small deformations except for light polonium isotopes with N≦112, nearly all the calculated high-K states have large axially deformed shapes (see Tables I and II), indicating significant shape polarizations of the broken pairs of nucleons.
Further, we found that the orbital blockings can stabilize the minimum of the configuration-constrained PES for these nuclei.

19. Support from experiment in neighbouring odd A nuclei.
discussion
Support from experiment in neighbouring odd A nuclei.
N. Fotiades et al.
PRC 56(1997)723;
A. N. Andreyev et al.
PRL 89 (1999)1819;

20. summary
summary
Systematic configuration-constrained PES calculations have been performed to study the shape-coexistence of two-qp isomeric states in neutron-deficient Hg, Pb, and Po isotopes.
Calculations are in good agreement with available experimental data.
An abundance of high-K states are predicted to exist at both prolate and oblate deformations.
The high-K states are relatively rigid and well-deformed compared to the respective g.s.s, hence providing favourable conditions for the formation of high-K isomers.

21. 谢谢