Shell structure of $^{43}$S and collapse of the $N=28$ shell closure

TL;DR

This study investigates the shell structure of neutron-rich isotope $^{43}$S, revealing a rapid collapse of the $N=28$ shell closure through experimental spectroscopy and comparison with shell model calculations.

Contribution

It provides new experimental data on $^{43}$S's level structure and demonstrates that the $N=28$ shell closure breaks down faster than predicted by existing models.

Findings

Strong intruder component in $^{44}$S ground state

Rapid breakdown of the $N=28$ shell closure

Discrepancy between experimental data and shell model predictions

Abstract

The single-particle structure of the $N=27$ isotones provides insights into the shell evolution of neutron-rich nuclei from the doubly-magic $^{48}$Ca toward the drip line. $^{43}$S was studied employing the one-neutron knockout reaction from a radioactive $^{44}$S beam. Using a combination of prompt and delayed $\gamma$-ray spectroscopy the level structure of $^{43}$S was clarified. Momentum distributions were analyzed and allowed for spin and parity assignments. The deduced spectroscopic factors show that the $^{44}$S ground-state configuration has a strong intruder component. The results were confronted with shell model calculations using two effective interactions. General agreement was found between the calculations, but strong population of states originating from the removal of neutrons from the $2p_{3/2}$ orbital in the experiment indicates that the breakdown of the $N=28$ magic number is more rapid than the theoretical calculations suggest.