Beta-decay study of the shape coexistence in ⁹⁸Zr

Throughout the nuclear chart the evolution of a spherical ground-state shape into a deformed one is usually a gradual process, while in the Zr isotopic chain an abrupt shape transition is observed at N=60. This onset of deformation in ¹⁰⁰Zr was recently reproduced in Monte Carlo Shell Model calculations [1, 2]. It was also predicted that the same deformed configuration may coexist at higher excitation energies in ⁹⁸Zr isotope, which lies on the interface between spherical and deformed nuclear phases. While both theory and experiment [3,4,5,6] demonstrate a good overall description of the structure of the ⁹⁸Zr, the interpretation of the higher-lying shape coexisting bands is still uncertain. Thus, a β-decay experiment was performed at TRIUMF-ISAC facility using the 8π spectrometer with β-particle detectors to measure the branching and multipolarity mixing ratios for the transitions in ⁹⁸Zr. The data obtained with this setup allowed for the determination of branching ratios for very weak transitions important for assigning band structures. Furthermore, γ-γ angular correlation measurements enabled both spin assignments and mixing ratio determinations. The new results will be presented and discussed in relation to both the MCSM and recent IBM configuration mixing calculations.