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Measurements of the $^{96}$Zr($α$,n)$^{99}$Mo cross section for astrophysics and applications

The reaction $^{96}$Zr($α$,n)$^{99}$Mo plays an important role in $ν$-driven wind nucleosynthesis in core-collapse supernovae and is a possible avenue for medical isotope production. Cross section measurements were performed using the activation technique at the Edwards Accelerator Laboratory. Results were analyzed along with world data on the $^{96}{\rm Zr}(α,n)$ cross section and $^{96}{\rm Zr}(α,α)$ differential cross section using large-scale Hauser-Feshbach calculations. We compare our data, previous measurements, and a statistical description of the reaction. We find a larger cross section at low energies compared to prior experimental results, allowing for a larger astrophysical reaction rate. This may impact results of core-collapse supernova $ν$-driven wind nucleosynthesis calculations, but does not significantly alter prior conclusions about $^{99}{\rm Mo}$ production for medical physics applications. The results from our large-scale Hauser-Feshbach calculations demonstrate that phenomenological optical potentials may yet be adequate to describe $(α,n)$ reactions of interest for $ν$-driven wind nucleosynthesis, albeit with regionally-adjusted model parameters.