Prolate-oblate phase transition in the Hf-Hg mass region

Experimental data in the Hf-Hg mass region indicate the presence of a prolate-oblate phase transition. The transition in which gamma-soft nuclei exhibit a first-order quantum phase transition in their shape is of the type that was recently proposed on very general grounds using Landau theory. The transition is situated close to the O(6) limit of the interacting boson model which is indeed found empirically in this mass region. Our study also hints at explaining why the quadrupole moments in Pt isotopes deviate from the O(6) value and confirms the recently proposed prolate-oblate phase transition with experimental data.