Shape coexistence in 94Zr from a model-independent analysis

Abstract

Low-lying states of 94Zr were investigated via low-energy multi-step Coulomb excitation. From the measured γ-ray yields, 16 reduced E2 transition probabilities between low-spin states were determined, together with the spectroscopic quadrupole moments of the 2+1,2 states. Based on this information, for the first time in the Zr isotopic chain, the shapes of the 0+1,2 states including their deformation softness were inferred in a model-independent way using the quadrupole sum rules approach. The ground state of 94Zr possesses a rather diffuse shape associated with a spherical configuration, while the 0+2 state is triaxial tending towards oblate and more strongly deformed. The observed features of shape coexistence in 94Zr are consistent with both Monte-Carlo shell-model predictions and IBM-CM calculations, and provide model-independent constraints on the shape character assigned in the IBM-CM to the intruder configuration in 92–96Zr.