Direct mass measurements of neutron-rich $^{86}$Kr projectile fragments and the persistence of neutron magic number $N$ = 32 in Sc isotopes

TL;DR

This study reports direct mass measurements of neutron-rich isotopes, revealing a strong sub-shell closure at neutron number N=32 in Sc isotopes, indicating persistent neutron magicity.

Contribution

First direct mass measurements of neutron-rich $^{86}$Kr projectile fragments, confirming the neutron magic number N=32 in Sc isotopes with improved precision.

Findings

New mass excesses for $^{52-54}$Sc with increased binding energies.

Evidence of a strong sub-shell closure at N=32 in Sc isotopes.

Enhanced understanding of neutron shell evolution in neutron-rich nuclei.

Abstract

In this paper, we present direct mass measurements of neutron-rich $^{86}$Kr projectile fragments conducted at the HIRFL-CSR facility in Lanzhou by employing the Isochronous Mass Spectrometry (IMS) method. The new mass excesses of $^{52-54}$Sc nuclides are determined to be -40492(82), -38928(114), -34654(540) keV, which show a significant increase of binding energy compared to the reported ones in the Atomic Mass Evaluation 2012 (AME12). In particular, $^{53}$Sc and $^{54}$Sc are more bound by 0.8 MeV and 1.0 MeV, respectively. The behavior of the two neutron separation energy with neutron numbers indicates a strong sub-shell closure at neutron number $N$ = 32 in Sc isotopes.