Mass of astrophysically relevant $^{31}$Cl and the breakdown of the isobaric multiplet mass equation

TL;DR

This paper reports a precise measurement of the mass of $^{31}$Cl, revealing deviations from the isobaric multiplet mass equation and providing improved data crucial for understanding astrophysical processes like x-ray bursts.

Contribution

The study provides the most precise mass measurement of $^{31}$Cl and demonstrates the breakdown of the quadratic isobaric multiplet mass equation, introducing a non-zero cubic term.

Findings

Mass of $^{31}$Cl measured with high precision.

Quadratic isobaric multiplet mass equation fails for A=31, T=3/2 quartet.

New $S_p$ value constrains astrophysical models of x-ray bursts.

Abstract

The mass of $^{31}$Cl has been measured with the JYFLTRAP double Penning trap mass spectrometer at the Ion-Guide Isotope Separator On-Line (IGISOL) facility. The determined mass-excess value, -7034.7(34) keV, is 15 times more precise than in the Atomic Mass Evaluation 2012. The quadratic form of the isobaric multiplet mass equation for the T=3/2 quartet at A=31 fails ($\chi^2_n$=11.6) and a non-zero cubic term, d=-3.5(11) keV, is obtained when the new mass value is adopted. $^{31}$Cl has been found to be less proton-bound with a proton separation energy of $S_p$=265(4) keV. Energies for the excited states in $^{31}$Cl and the photodisintegration rate on $^{31}$Cl have been determined with significantly improved precision using the new $S_p$ value. The improved photodisintegration rate helps to constrain astrophysical conditions where $^{30}$S can act as a waiting point in the rapid proton capture process in type I x-ray bursts.