New experimental $^{23}$Na($\alpha,p$)$^{26}$Mg Reaction Rate for Massive Star and Type-Ia Supernova models

TL;DR

This paper presents new experimental measurements of the $^{23}$Na($ ext{α}$,p)$^{26}$Mg reaction rate, significantly reducing uncertainties in nucleosynthesis models for massive stars and supernovae.

Contribution

It provides the first directly measured angular distributions to resolve discrepancies in reaction rates, leading to a more accurate and precise reaction rate with 30% uncertainty.

Findings

Derived a new reaction rate with 30% uncertainty

Reduced $^{26}$Al and $^{23}$Na production uncertainties to within 8%

Constrained $^{23}$Na production impact in supernovae to within 15%

Abstract

The $^{23}$Na($\alpha,p$)$^{26}$Mg reaction has been identified as having a significant impact on the nucleosynthesis of several nuclei between Ne and Ti in type-Ia supernovae, and of $^{23}$Na and $^{26}$Al in massive stars. The reaction has been subjected to renewed experimental interest recently, motivated by high uncertainties in early experimental data and in the statistical Hauser-Feshbach models used in reaction rate compilations. Early experiments were affected by target deterioration issues and unquantifiable uncertainties. Three new independent measurements instead are utilizing inverse kinematics and Rutherford scattering monitoring to resolve this. In this work we present directly measured angular distributions of the emitted protons to eliminate a discrepancy in the assumptions made in the recent reaction rate measurements, which results in cross sections differing by a factor of 3. We derive a new combined experimental reaction rate for the $^{23}$Na($\alpha,p$)$^{26}$Mg reaction with a total uncertainty of 30% at relevant temperatures. Using our new $^{23}$Na($\alpha,p$)$^{26}$Mg rate, the $^{26}$Al and $^{23}$Na production uncertainty is reduced to within 8%. In comparison, using the factor of 10 uncertainty previously recommended by the rate compilation STARLIB, $^{26}$Al and $^{23}$Na production was changing by more than a factor of 2. In type-Ia supernova conditions, the impact on production of $^{23}$Na is constrained to within 15%.