Constraining (a,n) cross sections with indirect measurements

The efficacy of the $s$-process in the production of heavy elements is influenced by a number of factors, including the number of neutrons available for neutron-capture reactions. Neutrons are produced by the $^{13}$C($\alpha,n$)$^{16}$O and $^{22}$Ne($\alpha,n$)$^{25}$Mg reactions, neutrons can be absorped by $^{16}$O to make $^{17}$O from which neutrons may be recycled through the $^{17}$O($\alpha,n$)$^{20}$Ne reaction or lost permanently through the $^{17}$O($\alpha,\gamma$)$^{21}$Ne reaction. In this talk, the utility of indirect measurements in constraining ($\alpha,n$) cross sections will be discussed, with particular focus on the $^{22}$Ne($\alpha,n$)$^{25}$Mg and $^{17}$O($\alpha,n$)$^{20}$Ne reactions and their application in $s$-process nucleosynthesis.