$\mathbf{N}=32$ shell closure below calcium: Low-lying structure of ${}^{50}$Ar

Abstract

Low-lying excited states in the $N=32$ isotope ${}^{50}$Ar were investigated by in-beam $\gamma$-ray spectroscopy following proton- and neutron-knockout, multi-nucleon 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 $\gamma \gamma$ 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 $4^{+}$ state could also correspond to a $2^{+}$ state.

arXiv commentAccepted for Phys. Rev. C

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• Investigating nuclear structure near $N=32$ and $N=34$: Precision mass measurements of neutron-rich Ca, Ti and V isotopes
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• Effective polarization in proton-induced $\alpha$ knockout reactions
• Evolution of shell structure at $\mathbf{N}=32$ and 34: Insights from realistic nuclear forces
• Systematic analysis of the nuclear absorption effect on the cross section of the knockout reaction