Probing the N = 32 shell closure below the magic proton number Z = 20: Mass measurements of the exotic isotopes 52,53K

TL;DR

This study provides the first mass measurements of isotopes 52,53K below Z=20, confirming a neutron-shell closure at N=32 and supporting its doubly-magic character through experimental and theoretical analysis.

Contribution

It presents the first mass measurements of 52,53K isotopes below Z=20, confirming the N=32 shell closure and challenging existing nuclear models.

Findings

A 3 MeV shell gap at N=32 was observed.

The isotopes exhibit doubly-magic characteristics.

Theoretical models qualitatively reproduce the shell effect.

Abstract

The recently confirmed neutron-shell closure at N = 32 has been investigated for the first time below the magic proton number Z = 20 with mass measurements of the exotic isotopes 52,53K, the latter being the shortest-lived nuclide investigated at the online mass spectrometer ISOLTRAP. The resulting two-neutron separation energies reveal a 3 MeV shell gap at N = 32, slightly lower than for 52Ca, highlighting the doubly-magic nature of this nuclide. Skyrme-Hartree-Fock-Boguliubov and ab initio Gorkov-Green function calculations are challenged by the new measurements but reproduce qualitatively the observed shell effect.