Reaction rates of $^{64}$Ge($p,γ$)$^{65}$As and $^{65}$As($p,γ$)$^{66}$Se and the extent of nucleosynthesis in type I X-ray bursts

Y. H. Lam, J. J. He, A. Parikh, B. A. Brown, M. Wang, B. Guo, Y. H. Zhang, X. H. Zhou, H. S. Xu

Published 2015-05-09Version 1

The extent of nucleosynthesis in models of type I X-ray bursts and the associated impact on the energy released in these explosive events are sensitive to nuclear masses and reaction rates around the $^{64}$Ge waiting point. Using a recent high precision mass measurement of $^{65}$As along with large-scale shell model calculations, we have determined new thermonuclear rates of the $^{64}$Ge($p$,$\gamma$)$^{65}$As and $^{65}$As($p$,$\gamma$)$^{66}$Se reactions. We examine the impact of available rates for these two reactions through a representative one-zone X-ray burst model. We find that our recommended rates may strongly suppress the flow of abundances toward $A\approx100$, in sharp contrast to recent work claiming that $^{64}$Ge is not a significant $rp$-process waiting point. Indeed, the summed mass fractions for species with $A > 70$ varies by about factors of 3 or 2 depending upon the adopted $^{64}$Ge($p$,$\gamma$)$^{65}$As or $^{65}$As($p$,$\gamma$)$^{66}$Se rates, respectively. Furthermore, the predictions for nuclear energy generation rate E$_\mathrm{gen}$ at late times during the burst varies rather significantly between the models using the different rates, with differences as large as about a factor of 2.