N=32 shell closure below calcium: Low-lying structure of Ar 50

Abstract

Low-lying excited states in the N=32 isotope Ar50 were investigated by in-beam γ-ray spectroscopy following proton- and neutron-knockout, multinucleon removal, and proton inelastic scattering at the RIKEN Radioactive Isotope Beam Factory. The energies of the two previously reported transitions have been confirmed, and five additional states are presented for the first time, including a candidate for a 3- state. The level scheme built using γγ coincidences was compared to shell-model calculations in the sd-pf model space and to ab initio predictions based on chiral two- and three-nucleon interactions. Theoretical proton- and neutron-knockout cross sections suggest that two of the new transitions correspond to 2+ states, while the previously proposed 41+ state could also correspond to a 2+ state. © 2020 authors. Published by the American Physical Society.