New 26P(p, γ)27S Thermonuclear Reaction Rate and Its Astrophysical Implications in the rp-process

Abstract

Accurate nuclear reaction rates for ^26 P( p , γ ) ^27 S are pivotal for a comprehensive understanding of the rp -process nucleosynthesis path in the region of proton-rich sulfur and phosphorus isotopes. However, large uncertainties still exist in the current rate of ^26 P( p , γ ) ^27 S because of the lack of nuclear mass and energy level structure information for ^27 S. We reevaluate this reaction rate using the experimentally constrained ^27 S mass, together with the shell model predicted level structure. It is found that the ^26 P( p , γ ) ^27 S reaction rate is dominated by a direct capture reaction mechanism despite the presence of three resonances at E = 1.104, 1.597, and 1.777 MeV above the proton threshold in ^27 S. The new rate is overall smaller than the other previous rates from the Hauser–Feshbach statistical model by at least 1 order of magnitude in the temperature range of X-ray burst interest. In addition, we consistently update the photodisintegration rate using the new ^27 S mass. The influence of new rates of forward and reverse reaction in the abundances of isotopes produced in the rp -process is explored by postprocessing nucleosynthesis calculations. The final abundance ratio of ^27 S/ ^26 P obtained using the new rates is only 10% of that from the old rate. The abundance flow calculations show that the reaction path ^26 P( p , γ ) ^27 S( β ^+ , ν ) ^27 P is not as important as previously thought for producing ^27 P. The adoption of the new reaction rates for ^26 P( p , γ ) ^27 S only reduces the final production of aluminum by 7.1% and has no discernible impact on the yield of other elements.

Keywords

• Reaction rates
• X-ray bursts
• Nuclear physics
• Nuclear abundances
• Explosive nucleosynthesis