# Neutron spectroscopy of $^{26}$Mg states: constraining the stellar neutron source $^{22}$Ne($\alpha, n$)$^{25}$Mg

## TL;DR

This study provides precise measurements of neutron capture cross sections on magnesium-25, refining nuclear reaction rates relevant for stellar neutron sources and impacting models of stellar evolution.

## Contribution

It offers improved resonance data and reaction rate estimates for $^{25}$Mg(n,γ)$^{26}$Mg and constrains the stellar neutron source reactions involving $^{22}$Ne.

## Key findings

- Refined $^{25}$Mg(n,γ)$^{26}$Mg cross sections.
- Unambiguous spin/parity assignments for $^{26}$Mg states.
- Potentially higher ($ ext{α, n}$)/($ ext{α, γ}$) ratio in stellar environments.

## Abstract

This work reports on accurate, high-resolution measurements of the $^{25}$Mg($n, \gamma$)$^{26}$Mg and $^{25}$Mg($n, tot$) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved $^{25}$Mg($n, \gamma$)$^{26}$Mg parametrization. The relevant resonances for $n+^{25}$Mg were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in $^{26}$Mg. With this information experimental upper limits of the reaction rates for $^{22}$Ne($\alpha, n$)$^{25}$Mg and $^{22}$Ne($\alpha, \gamma$)$^{26}$Mg were established, potentially leading to a significantly higher ($\alpha, n$)/($\alpha, \gamma$) ratio than previously evaluated. The impact of these results have been studied for stellar models in the mass range 2 to 25 $M_{\odot}$.