Secondary γ -ray decays from the partial-wave T matrix with an R -matrix application to N15(p,α1γ)C12

The secondary $\ensuremath{\gamma}$ rays emitted following a nuclear reaction are often relatively straightforward to detect experimentally. Despite the large volume of such data, a practical formalism for describing these $\ensuremath{\gamma}$ rays in terms of partial-wave $T$-matrix elements has never been given. The partial-wave formalism is applicable when $R$-matrix methods are used to describe the reaction in question. This paper supplies the needed framework, and it is demonstrated by the application to the $^{15}\mathrm{N}(p,{\ensuremath{\alpha}}_{1}\ensuremath{\gamma})^{12}\mathrm{C}$ reaction.