Low-lying intruder and tensor-driven structures in As-82 revealed by beta decay at a new movable-tape-based experimental setup

The $\ensuremath{\ beta}$ decayof $^{82}\mathrm{Ge}$ was re-investigated using the newly commissioned tape station BEDO at the electron-driven ISOL ( isotope separationon line) facility ALTO operated by the Institut de Physique Nucl\'eaire, Orsay. The original motivation of this work was focused on the sudden occurrence in the light $N=49$ odd-odd isotonic chain of a large number of $J\ensuremath{\le}1$ states (positive or negative parity) in $^{80}\mathrm{Ga}$ by providing a reliable intermediate example, viz., $^{82}\mathrm{As}$. The extension of the $^{82}\mathrm{As}$ level scheme towards higher energies from the present work has revealed three potential ${1}^{+}$ states above the already known one at 1092 keV. In addition our data allow ruling out the hypothesis that the 843 keV level could be a ${1}^{+}$ state. A detailed analysis of the level scheme using both an empirical core-particle coupling model and a fully microscopic treatment within a Skyrme-QRPA (quasiparticle random-phase approximation) approach using the finite-rank separable approximation was performed. From this analysis two conclusions can be drawn: (i) the presence of a large number of low-lying low-spin negative parity states is due to intruder statesstemming from above the $N=50$ shell closure, and (ii) the sudden increase, from $^{82}\mathrm{As}$ to $^{80}\mathrm{Ga}$, of the number of low-lying ${1}^{+}$ states and the corresponding Gamow-Teller fragmentation are naturally reproduced by the inclusion of tensor correlations and couplings to 2p-2h excitations.