Improved S factor of the C12(p,γ)N13 reaction at E=320–620 keV and the 422 keV resonance

The ¹²C(p,γ)¹³N reaction is the onset process of both the CNO and hot CNO cycles that drive massive star, red and asymptotic giant branch star, and novae nucleosynthesis. The ¹²C(p,γ)¹³N rate affects the final abundances of the stable ¹²´¹³C nuclides with ramifications for meteoritic carbon isotopic abundances and the s-process neutron source strength. Here, an underground measurement of the ¹²C(p,γ)¹³N cross section is reported. The present data, obtained at the Felsenkeller shallow-underground laboratory in Dresden (Germany), encompass the 320–620 keV center of mass energy range to include the wide and poorly constrained E=422 keV resonance that dominates the rate at high temperatures. This work's S-factor results, lower than literature by 25%, are included in a comprehensive R-matrix fit, and the energy of the 12+ first excited state of ¹³N is found to be 2369.6(4) keV with a radiative and proton width of 0.49(3) eV and 34.9(2) keV, respectively. A reaction rate, based on the present R-matrix fit and extrapolation, is suggested.