Shape coexistence and the role of axial asymmetry in 72Ge

Abstract The quadrupole collectivity of low-lying states and the anomalous behavior of the 0 2 + and 2 3 + levels in 72 Ge are investigated via projectile multi-step Coulomb excitation with GRETINA and CHICO-2. A total of forty six E 2 and M 1 matrix elements connecting fourteen low-lying levels were determined using the least-squares search code, gosia . Evidence for triaxiality and shape coexistence, based on the model-independent shape invariants deduced from the Kumar–Cline sum rule, is presented. These are interpreted using a simple two-state mixing model as well as multi-state mixing calculations carried out within the framework of the triaxial rotor model. The results represent a significant milestone towards the understanding of the unusual structure of this nucleus.