Inverse-kinematics proton scattering from $^{42,44}$S, $^{41,43}$P and the collapse of the $N=28$ major shell closure

TL;DR

This study investigates the structure of neutron-rich isotopes $^{42,44}$S and $^{41,43}$P through inverse-kinematics proton scattering, revealing insights into shell evolution and favoring the SDPF-MU interaction model.

Contribution

It provides new experimental data on deformation lengths and neutron-to-proton matrix element ratios, and compares shell model interactions, highlighting the collapse of the $N=28$ shell closure.

Findings

Deformation lengths for $^{42,44}$S determined from proton scattering.

Neutron-to-proton matrix element ratios calculated for $^{42,44}$S.

Results favor the SDPF-MU shell model interaction.

Abstract

Excited states of the neutron-rich isotopes $^{42,44}$S and $^{41,43}$P have been studied via inverse-kinematics proton scattering from a liquid hydrogen target, using the GRETINA $\gamma$-ray tracking array to extract inelastic scattering cross sections. Deformation lengths of the $2^+_1$ excitations in $^{42,44}$S have been determined and, when combined with deformation lengths determined with electromagnetic probes, yield the ratio of neutron-to-proton matrix elements $M_n/M_p$ for the $2^+_1$ excitations in these nuclei. The present results for $^{41,43}$P$(p,p')$ are used to compare two shell model interactions, SDPF-U and SDPF-MU. As in a recent study of $^{42}$Si, the present results on $^{41,43}$P favor the SDPF-MU interaction.