The $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction -- state of the art, astrophysics, and perspectives

TL;DR

This paper reviews the current understanding, experimental challenges, and astrophysical significance of the $^{22}$Ne($ extalpha$,n)$^{25}$Mg reaction, a key neutron source in stellar nucleosynthesis.

Contribution

It provides a comprehensive overview of recent experimental efforts, uncertainties, and future perspectives on measuring the reaction cross section at astrophysically relevant energies.

Findings

Recent measurements have improved understanding of the reaction cross section.

Significant uncertainties remain at low energies near the neutron threshold.

The reaction critically influences s-process nucleosynthesis in stars.

Abstract

One of the most important stellar neutron sources is the $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction, which gets activated both during the helium intershell burning in asymptotic giant branch stars and in core helium and shell carbon burning in massive stars. The $^{22}$Ne($\alpha$,n)$^{25}$Mg reaction serves as the main neutron producer for the weak s-process and provides a short but strong neutron exposure during the helium flash phase of the main s-process, significantly affecting the abundances at the s-process branch points. The cross section needs to be known at very low energies, as close as possible to the neutron threshold at $E_\alpha = 562$ keV ($Q = - 478$ keV), but both direct and indirect measurements have turned out to be very challenging, leading to significant uncertainties. Here we discuss the current status of the reaction, including recent and upcoming measurements, and provide a discussion on the astrophysical implications as well as an outlook into the near future.