Examination of Astrophysical S-Factor and Non-Resonant Rates of the 64Ge(p,γ)65As Reaction

Abstract

The 64Ge(p,γ)65As reaction rates strongly impact the predictions of the energy generation and isotopic abundance in the rp-process in X-ray bursts. However, the rates are ambiguous at present due to the lack of experimental cross section and the uncertainty in the non-resonant reaction rates. To provide informative data for the astrophysical rates of the 64Ge(p,γ)65As reaction, we evaluate the astrophysical S factor and direct capture rates of the 64Ge(p,γ)65As reaction using the cross sections relied on the statistical theory with various mass models. The S factors at 0 energy were found to be S(0) = 7.2×105 and 1.1×106 MeV.barn for the Finite-Range Droplet Model (FRDM) and the extended Thomas-Fermi (ETFSI) mass models, respectively. These values are about 4 orders of magnitude different from the value obtained in previous study. The empirical parameters for the non-resonant-rate approximations were also deduced for the 64Ge(p,γ)65As reaction and its photodisintegration. By considering the results in this study together with those obtained in the previous work, we confirm that a strong waiting point at the 64Ge nucleus is still a doubt because of large uncertainty of the S factor and non-resonant rates. The results in this study are useful for a better understanding of the X-ray burst properties and reaction flow at 64Ge in the rp-process.
 HIGHLIGHTS
 
 Large discrepancy up to 4 orders of magnitude in the S factor at zero energy was found
 The strength of the waiting point at 64Ge in the rp-process is still questionable
 The astrophysical rates of the 64Ge(p,γ)65As reaction are very uncertain due to the S-factor uncertainty
 The non-resonant rates of the 64Ge(p,γ)65As reaction estimated using statistical method are not significantly impacted by the FRDM and ETFSI mass models
 
 GRAPHICAL ABSTRACT