Constraints on the $^{22}Ne(\alpha,n)^{25}$Mg s-process neutron source from analysis of $^{nat}Mg+n$ total and $^{25}Mg(n,\gamma)$ cross sections

Abstract

I have analyzed previously reported $^{\text{nat}}$Mg+\textit{n%} total and $^{25}$Mg(\textit{n},$\gamma $) cross sections to obtain a much improved set of resonance parameters for states in $^{26}$Mg between threshold and the lowest observed $^{22}$Ne($\alpha $,\textit{n})$^{25}$Mg resonance, and an improved estimate of the uncertainty in the $^{22}$Ne($% \alpha $,\textit{n})$^{25}$Mg reaction rate. For example, definitely two, and very likely at least four, of the states in this region have natural parity and hence can contribute to the $^{22}$Ne($\alpha $,\textit{n})$^{25}$% Mg reaction, but two others definitely have non-natural parity and so can be eliminated from consideration. As a result, a recent evaluation in which it was assumed that only one of these states has natural parity has underestimated the reaction rate uncertainty by at least a factor of ten, whereas evaluations that assumed all these states could contribute probably have overestimated the uncertainty.