Spherical-oblate shape coexistence in $^{94}$Zr from a model-independent analysis
nucl-ex
/ Authors
N. Marchini, M. Rocchini, M. Zielinska, A. Nannini, D. T. Doherty, N. Gavrielov, P. E. Garrett, K. Hadynska-Klek, A. Goasduff, D. Testov
and 26 more authors
S. D. Bakes, D. Bazzacco, G. Benzoni, T. Berry, D. Brugnara, F. Camera, W. N. Catford, M. Chiari, F. Galtarossa, N. Gelli, A. Gottardo, A. Gozzelino, A. Illana, J. Keatings, D. Mengoni, L. Morrison, D. R. Napoli, M. Ottanelli, P. Ottanelli, G. Pasqualato, F. Recchia, S. Riccetto, M. Scheck, M. Siciliano
/ Abstract
Low-lying states of $^{94}$Zr were investigated via low-energy multi-step Coulomb excitation. From the measured $γ$-ray yields, 13 reduced 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 oblate and more strongly deformed. The observed features of shape coexistence in $^{94}$Zr are in agreement with Monte-Carlo shell-model predictions, and the present results are vital to refine the IBM-CM description of the Zr isotopes around $A\approx 100$ in terms of an intertwined quantum phase transition.