Isomers and oblate collectivity at high spin in neutron-rich Pt isotopes

Abstract

Isomers and high-spin structures with rotation-aligned oblate configurations have been studied in several Pt isotopes. The 12 + states in the even Pt isotopes from 192–198 Pt are found to be metastable, and have ( i 13/2 ) 2 neutron character. The progression of E 2 transition probabilities from the 12 + to 10 + states across the Pt isotopic chain implies reduction in collectivity, followed by an abrupt decrease at N =120 ( 198 Pt). This behavior is quite distinct from the gradual decrease of B ( E 2) values near the respective ground states. A large contribution from aligned angular momentum, to the rotational sequences built on the 12 + states, is visible. This is due to the relatively small crossing frequencies for nucleons in low-Ω orbitals at oblate deformation in comparison to higher values for prolate shapes. As a result, oblate rotation is found to be increasingly favored for higher neutron numbers.