Cross-shell excitations in Ca46 studied with fusion reactions induced by a reaccelerated rare isotope beam

Abstract

Discovering unexplored high-spin states in neutron-rich nuclei can open up a new direction to study band structure and the associated shell structure in isospin-asymmetric many-body systems. However, experimental reach has so far been limited to neutron-deficient or stable nuclei which are preferentially produced in fusion reactions used in such studies. Here, we report the first $\ensuremath{\gamma}$-ray spectroscopy with fusion reactions using a reaccelerated rare-isotope beam of $^{45}\mathrm{K}$ performed at the ReA3 facility of the National Superconducting Cyclotron Laboratory. Using particle and $\ensuremath{\gamma}$-ray coincidence techniques, three new higher-lying states around 6 MeV and five new $\ensuremath{\gamma}$-ray transitions were identified for $^{46}\mathrm{Ca}$, suggesting three independent band structures formed from different particle-hole configurations. The rotational-like band built on the ${0}_{2}^{+}$ state is established up to the tentatively assigned ${6}_{2}^{+}$ state. New results are compared to large-scale shell model calculations, confirming the validity of the effective interaction describing particle-hole excitations across the $Z=20$ and $N=28$ shell gaps in the vicinity of doubly magic $^{48}\mathrm{Ca}$.