Mass measurements of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ga</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>60</mml:mn><mml:mtext>–</mml:mtext><mml:mn>63</mml:mn></mml:mrow></mml:mmultiscripts></mml:math> reduce x-ray burst model uncertainties and extend the evaluated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math> isobaric multiplet mass equation
S. F. Paul, J. Bergmann, J. D. Cardona, K. Dietrich, E. Dunling, Z. Hockenbery, C. Hornung, C. Izzo, Andrew Jacobs, A. Javaji, B. Kootte, Y. Lan, E. Leistenschneider, E. M. Lykiardopoulou, Ish Mukul, T. Murböck, W. S. Porter, R. Silwal, M. B. Smith, Jon Ringuette, T. Brunner, T. Dickel, I. Dillmann, G. Gwinner, M. MacCormick, M. P. Reiter, H. Schatz, N. A. Smirnova, J. Dilling, A. A. Kwiatkowski
Abstract
We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of $^{60\text{--}63}\mathrm{Ga}$ performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of $^{61}\mathrm{Ga}$ and mark the first direct mass measurement of $^{60}\mathrm{Ga}$. The improved precision of the $^{61}\mathrm{Ga}$ mass has important implications for the astrophysical $rp$ process, as it constrains essential reaction $Q$ values near the $^{60}\mathrm{Zn}$ 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 $^{60}\mathrm{Ga}$ 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 $^{60}\mathrm{Ga}$ further enables us to extend the evaluated $T=1$ isobaric multiplet mass equation up to $A=60$.