Investigation of secondary γ -ray angular distributions using the N15(p,α1γ)C12 reaction

The observation of secondary γ-rays provides an alternative method of measuring cross sections that populate excited final states in nuclear reactions. The angular distributions of these γ-rays also provide information on the underlying reaction mechanism. Despite a large amount of data of this type in the literature, publicly available R-matrix codes do not have the ability to calculate these types of angular distributions. In this report, the mathematical formalism derived in Brune and deBoer is implemented in the R-matrix code AZURE2 and calculations are compared with previous data from the literature for the 15N(p, α1γ) 12C* reaction. In addition, new measurements, made at the University of Notre Dame Nuclear Science Laboratory using the Hybrid Array of Gamma Ray Detectors (HAGRiD), are reported that span an energy range from Ep = 0.88 to 4.0 MeV. Excellent agreement between data and the phenomenological fit is obtained up to the limit of the previous fit at Ep = 2.0 MeV and the R-matrix fit is extended from Ex ≈ 13.5 up to Ex ≈ 15.3 MeV, where 15N+p and 12C+α reactions are fit simultaneously for the first time. An excellent reproduction of the 15N(p, α1γ) 12C* and 12C(α, α) 12C data is achieved, but inconsistencies and difficulty in fitting other data is encountered and discussed.