R-matrix analyses of secondary γ-ray angular distributions for recent reaction studies at the University of Notre Dame

At the University of Notre Dame's Nuclear Science Laboratory we have recently studied ¹³C(α,n)¹⁶O as a background for neutrino experiments, ¹⁷O(α,n)²⁰Ne for its role in the s-process and ¹⁰B(α,n)¹³N as a background for low energy underground nuclear astrophysics experiments at CASPAR and a possible key nucleosynthesis reaction in first generation stars. At the energies studied, all of these reactions produce secondary γ-rays from the population of excited states in the final nucleus. In many situations, especially when neutrons are the primary exit particle, detection of secondary γ-rays has several experimental advantages. These secondary γ-rays are in general anisotropic and measurements of the angular distributions give constraints on the spin-parities of populated resonances. We have performed a detailed experiment of this type for the ¹⁷O(α,n)²⁰Ne reaction using the HAGRiD array. In this talk I will describe the analysis of these reactions using the R-matrix technique and giving benchmark calculations for the well-studied ¹⁵N(p,α)¹⁶O reaction.