Deformation crossing near the first-order shape-phase transition in 152-156Gd

Quantitative evidence of the spherical-to-deformed shape phase transition near N=90 is given using the model-independent quadrupole shape invariant q2, which provides a measure of the β deformation of a given nucleus. This shape invariant is obtained using experimental B(E2) values for the ground state band and first excited 0+ band of Gd isotopes around N=90, and is compared to calculations within the interacting boson model. Near the shape phase transition, the ground and excited 0+ band deformations are observed to cross