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

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 ($\ddot{I}{‡}_n^2$=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.

6 pages, 4 figures, submitted to Phys. Rev. C Rapid Comm