Measurement and R-Matrix Analysis of the 15N(p,g)16O Reaction Cross Section

Along with the p-p chains, the CNO cycle is the main source of energy production inside of stars with masses larger than the sun. The ¹⁵N + p reaction is the first branch point of this cycle, where the (p,&alpha) reaction returns material to the CN cycle and the (p,&gamma) reaction leads to the NO cycle, and thus plays a role in determining the final energy production of the process and influences the abundances of oxygen isotopes. This project involves obtaining new measurements for the ¹⁵N(p,&gamma)¹⁶O reaction. Dominated by two broad resonances at E_p = 338 and 1028 keV, measurements of this reaction were performed in the proton energy range from 1800 keV down to 130 keV. Particular attention was paid to the area between the two dominant resonances, along with the low energy region, as these are the most important regions in determining the S(0) extrapolations. To obtain this measurement, article accelerators at both the University of Notre Dame's Nuclear Science Laboratory (NSL) and the Underground Laboratory for Nuclear Astrophysics (LUNA) in Gran Sasso, Italy were used. In both locations, high purity germanium detectors were used to detect &gamma-rays from the reaction of around 13 MeV. It was not possible to measure down to energies corresponding to relevant stellar environment temperatures, and so theoretical fits and extrapolations to the data must be made. To this end, the multi-level, multi-channel R-matrix code AZURE was used. The resulting S factor calculations were used to calculate new reaction rates for different temperature values, and gives up to a factor of 2 difference from currently used compilations~cite{Angulo1999}.