Active Target Measurement of the ^25,26Mg(α,n)^28,29Si Total Cross Section

The observation of gamma rays from the beta decay of ²⁶Al provides direct evidence of ongoing nucleosynthesis in the galaxy. While the observed galactic distribution of ²⁶Al points to massive stars as the main production sites, the underlying nuclear processes are uncertain. Sensitivity studies have found that two reactions contributing to the uncertainty of ²⁶Al production in massive stars are the ²⁵Mg(α,n)²⁸Si and ²⁶Mg(α,n)²⁹Si reactions. These reactions influence ²⁶Al production in stable and explosive C/Ne shell burning in massive stars. The ²⁶Mg(α,n)²⁹Si has also been found to have a direct influence on the isotopic ratio of ²⁹Si/³⁰Si found in pre-solar grains formed from supernova. Models of supernova nucleosynthesis have failed to reproduce this ratio. While previous measurements of these reactions have been made, reaction rates rely solely on statistical model calculations in energy ranges where experimental data is present and in good agreement. Below this energy range, the reaction rates are based on discrepant, unpublished thesis data. To resolve these issues, measurements of the ^25,26Mg(α,n)^28,29Si total cross sections were performed with a newly developed active target detector at The University of Notre Dame’s Nuclear Science Lab.