Mass measurements of $^{60-63}$Ga reduce x-ray burst model uncertainties and extend the evaluated $T=1$ isobaric multiplet mass equation

TL;DR

This study provides precise mass measurements of neutron-deficient gallium isotopes, significantly improving data accuracy, constraining astrophysical models of X-ray bursts, and extending the isobaric multiplet mass equation to higher mass numbers.

Contribution

It offers the first direct mass measurement of $^{60}$Ga and refines the mass of $^{61}$Ga, impacting astrophysical models and nuclear mass systematics.

Findings

$^{60}$Ga is proton-bound, defining the proton drip line.

Improved $^{61}$Ga mass constrains rp process reaction Q-values.

Extends the $T=1$ isobaric multiplet mass equation to $A=60$.

Abstract

We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of $^{60-63}$Ga performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of $^{61}$Ga and mark the first direct mass measurement of $^{60}$Ga. The improved precision of the $^{61}$Ga mass has important implications for the astrophysical rp process, as it constrains essential reaction Q-values near the $^{60}$Zn waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of X-ray burst models. The first-time measurement of the $^{60}$Ga ground-state mass establishes the proton-bound nature of this nuclide; thus, constraining the location of the proton drip line along this isotopic chain. Including the measured mass of $^{60}$Ga further enables us to extend the evaluated $T=1$ isobaric multiplet mass equation up to $A=60$.