Beta-decay study of the shape coexistence in ⁹⁸Zr

Anomalies in the systematics of nuclear properties challenge our understanding of the underlying nuclear structure. One such anomaly emerges in the Zr isotopic chain as a dramatic ground-state shape change, abruptly shifting from spherical into a deformed one at N=60. This research focuses on ⁹⁸Zr which lies on the interface between spherical and deformed phases. While past research provided an over-all understanding of ⁹⁸Zr's nuclear structure [1,2,3,4,5], most recent studies employing state-of-the-art theoretical models presented conflicting interpretations of its higher-lying bands [6,7].

A β-decay experiment was conducted at the TRIUMF-ISAC facility utilizing the 8π spectrometer to resolve these uncertainties. The obtained data allowed the determination of branching ratios for weak transitions, crucial for assigning band structures. Observing the key 155-keV 2₂⁺ → 0₃⁺ transition enabled the determination of its B(E2) value for the first time. Additionally, γ-γ angular correlation measurements allowed us to establish the 0⁺, 2⁺, and I = 1 natures for multiple newly observed and previously known (but not firmly assigned) states as well as mixing ratios. The new results revealed the collective character of certain key transitions, supporting the multiple shape coexistence interpretation provided by the framework of Monte Carlo Shell Model (MCSM). These results will be presented and discussed in relation to both MCSM and Interacting Boson Model with configuration mixing calculations.