Shape Coexistence in ${}^{94}$Zr from a Model-Independent Analysis

Abstract

Low-lying states of ${}^{94}$Zr were investigated via low-energy multi-step Coulomb excitation. From the measured ${\hat{I}}^3$-ray yields, \textcolor{black}{16} reduced \textcolor{black}{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 ${}^{94}$Zr possesses a rather diffuse shape associated with a spherical configuration, while the $0_2^{+}$ state is \textcolor{black}{triaxial tending towards} oblate and more strongly deformed. {\color{black}The observed features of shape coexistence in ${}^{94}$Zr 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 ${}^{92\text{–}96}$Zr.}

9 pages, 5 figures