Thermonuclear Reaction Rate of $^{30}$Si(p,$\gamma$)$^{31}$P

TL;DR

This study refines the $^{30}$Si(p,$ ext{γ}$)$^{31}$P reaction rate by measuring key resonances, significantly reducing uncertainties and impacting models of silicon synthesis in globular cluster environments.

Contribution

The paper provides new resonance strength measurements for the $^{30}$Si(p,$ ext{γ}$)$^{31}$P reaction, leading to a revised, lower reaction rate with reduced uncertainty.

Findings

Resonance strength at 435 keV was measured as (1.28 ± 0.25) × 10^{-4} eV.

Resonance strength at 501 keV was measured as (1.88 ± 0.14) × 10^{-1} eV.

The reaction rate at relevant temperatures is reduced by a factor of approximately 10.

Abstract

Silicon synthesis in high-temperature hydrogen burning environments presents one possible avenue for the study of abundance anomalies in globular clusters. This was suggested in a previous study, which found that the large uncertainties associated with the $^{30}$Si(p,$\gamma$)$^{31}$P reaction rate preclude a firm understanding of the stellar conditions that give rise to the Mg-K anti-correlation observed in the globular cluster NGC 2419. In an effort to improve the reaction rate, we present new strength measurements of the $E_r^{lab} = 435$ keV and $E_r^{lab} = 501$ keV resonances in $^{30}$Si(p,$\gamma$)$^{31}$P. For the former, which was previously unobserved, we obtain a resonance strength of $\omega\gamma = (1.28 \pm 0.25$) $\times 10^{-4}$ eV. For the latter, we obtain a value of $\omega\gamma = (1.88 \pm 0.14)$ $\times 10^{-1}$ eV, which has a smaller uncertainty compared to previously measured strengths. Based on these results, the thermonuclear reaction rate has been re-evaluated. The impact of the new measurements is to lower the reaction rate by a factor of $\approx$10 at temperatures important to the study of NGC 2419. The rate uncertainty at these temperatures has also been reduced significantly.