Bulg. J. Phys. vol.44 no.4 (2017), pp. 427-433

Shape Effects in E2 Transition Rates from Z ≈ 76 High-Spin Isomers

P.M. Walker
Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom
Abstract. It is well known that high-K isomers have strongly hindered electromagnetic decay rates. However, the situation is more subtle in shape-transition regions, where there are competing high-spin isomers associated with shape changes. Nevertheless, a previous analysis of E2 decay rates from isomers in N ≈ 76 (A ≈ 130) nuclides enabled a degree of separation to be made between high-K prolate states and low-K oblate states. The analysis exploited the dependence of E2 reduced hindrance factors, fν, on the product of the valence nucleon numbers, NpNn. The present work investigates the application of these ideas to data for neutron-rich Z ≈ 76 (A ≈ 180) nuclides. Despite few such isomer data being available, it is found that the reduced hindrance factors can be used to help in distinguishing between three different $E2$-transition types. In particular, the decays from high-K prolate isomers to the ground-state band are more hindered than the corresponding decays from low-K oblate isomers. Other decays from low-K oblate isomers have collective E2 transition rates. These features may be helpful in future studies of nuclides in the neutron-rich Z ≈ 76 region.

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