Absolute normalization of the ¹²C(p,γ)¹³N and ¹³C(p,γ₀)¹⁴N cross sections

The ¹²C(p,γ)¹³N and ¹³C(p,γ₀)¹⁴N reactions play a critical role in the Carbon-Nitrogen (CN) cycle. Surprisingly, the absolute normalization of the reaction rates for both reactions are quite uncertain. Both reactions have strong and broad resonances a few 100~keV above the proton threshold. We report here new measurements of the absolute ¹²C(p,γ)¹³N and ¹³C(p,γ₀)¹⁴N cross sections at the peaks of these resonances. The measurements were conducted by bombarding enriched ¹²C or ¹³C targets with proton beams and detecting the emitted γ rays with high-purity Ge detectors. The thicknesses of the carbon targets, which are essential for determining the absolute cross sections, were determined by deuteron energy loss and elastic α scattering measurements. The implications for the reaction rates of proton capture on carbon isotopes in the CN cycle will be discussed.