Shape evolution in neutron-rich Rh isotopes: First measurement of negative-parity isomers in 117,119Rh

Abstract

The β -delayed γ -ray spectroscopy of neutron-rich 117,119Rh isotopes has been investigated at the Radioactive Isotope Beam Factory of RIKEN. The 1/2− isomers in 117,119Rh have been identified for the first time. The systematics of energy differences between the 9/2+ and 1/2− states have been extended up to N=74, which shows a tendency to first increase with the neutron number N , then reach a maximum at N ≈ 68, and subsequently decrease. Self-consistent triaxial relativistic Hartree-Bogoliubov (TRHB) calculations highlight the crucial role of triaxial deformation, particularly in the positive-parity states, in driving the observed evolution of energy differences. A shape transition from axially symmetric to triaxial and back to axially symmetric deformation is suggested along the Rh isotopic chain. These findings provide new insights into the structure of neutron-rich nuclei in the A ∼ 110 region and motivate further studies of exotic isotopes in this region to explore the interplay between triaxiality and shell evolution.