Speaker
Description
The region near the doubly magic nucleus $^{78}$Ni (Z = 28, N = 50) plays a key role in understanding shell evolution and the balance between single-particle and collective degrees of freedom [1]. It represents a critical testing ground for theories of nuclear structure far from stability and for constraining models of r-process nucleosynthesis. In this context, neutron-rich zinc isotopes provide valuable insight into the strength of the N = 50 neutron shell gap and the onset of correlations as protons fill the f$_{5/2}$ and p${_3/2}$ orbitals. Previous studies in the region have suggested a competition between allowed Gamow–Teller (GT) and First-Forbidden (FF) $\beta$ transitions [2, 3], as well as between neutron and $\gamma$-ray emission from unbound states, but available high-resolution data remain incomplete and sometimes inconsistent.
To address these questions, $\beta$-decay studies of $^{80–82}$Zn were performed at ISOLDE (CERN) using the Lucrecia Total Absorption $\gamma$-ray Spectrometer (TAGS) [4] in the IS684 experiment. The technique provides high detection efficiency and is ideally suited to determine $\beta$-feeding distributions to high-lying states in the daughter Ga isotopes, avoiding systematic uncertainties inherent to high-resolution spectroscopy. The experiment aims to quantify the competition between GT and FF transitions beyond $^{78}$Ni and to identify $\gamma$-decay cascades from neutron-unbound states, providing experimental constraints on (n,$\gamma$) reaction rates relevant for astrophysical modeling [5, 6].
In this contribution, the status of the IS684 analysis will be presented. The experiment achieved high-quality data for the $\beta$ decays of $^{80-82}$Zn, benefitting from the purity and intensity of the ISOLDE beams and the high efficiency of the Lucrecia setup for the detection of gamma cascades. The aim is to provide improved $\beta$-strength distributions, accurate ground-state feedings, and revised $\beta$-delayed neutron emission probabilities (P$_n$), allowing for a deeper understanding of the structure of Ga isotopes and to examine the persistence of the N = 50 shell closure. The results will contribute to refining nuclear-structure models and improving astrophysical reaction networks involving zinc isotopes near the doubly magic $^{78}$Ni.