High-precision Penning trap mass measurements of neutron-rich chlorine isotopes at the N=28 shell closure

TL;DR

This study provides high-precision mass measurements of neutron-rich chlorine isotopes near the N=28 shell closure, improving accuracy significantly and comparing results with ab initio calculations to explore shell erosion.

Contribution

It presents the first high-precision mass measurements of $^{43-45}$Cl isotopes near the N=28 shell closure, with improved uncertainties and comparison to theoretical models.

Findings

Mass uncertainties reduced by up to a factor of 40.

Good agreement between measurements and ab initio calculations.

Insights into shell closure erosion at low proton numbers.

Abstract

Although it is known that the $N=28$ spherical shell closure erodes, the strength of the closure with decreasing proton number $Z<20$ is an open question in nuclear structure. In this region of interest, direct high-precision mass measurements of neutron-rich $^{43-45}$Cl isotopes were performed at the Low Energy Beam and Ion Trap (LEBIT) when coupled to the National Superconducting Cyclotron Lab. The resulting mass excesses (MEs) are ME($^{43}$Cl) = -24114.4(1.7) keV, ME($^{44}$Cl) = -20450.8(10.6) keV, and ME($^{45}$Cl) = -18240.1(3.7) keV, and improve the uncertainty of these masses by up to a factor of ~40 compared to the previous values reported in the 2020 Atomic Mass Evaluation. Comparison to $\textit{ab initio}$ calculations using the Valence-Space In-Medium Similarity Renormalization Group (VS-IMSRG) shows good agreement up to and including the closure.