study of the 13C(p,g)14N reaction at the Felsenkeller laboratory

The 13C(p,g)14N reactions take part in the CNO cycle, which is the dominant H-burning cycle in massive stars and in H-burning shell of Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stars, with 0.02 < T < 0.1 GK. Being a catalytic cycle, the CNO reactions not only convert four protons into one helium nucleus, but also govern the abundances of the C, N and O isotopes. In particular the 12C/13C ratio is a sensitive indicator of stellar nucleosynthesis, mixing processes and a useful tracer of Galactic chemical evolution. Presently the 12C/13C ratio in the Solar System is estimated to be of about 90(10) . A pos- sible origin for the elements in the Solar System are the AGB stars, which are prolific centers of nucleosynthesis. Nevertheless, more accurate insight into the mixing phenomena occurring inside these stars is needed in order to allow more precise predictions. Hints of AGB surface composition could come from the analysis of the SiC grains of the pristine meteorites. More- over the observation of RGB stars with masses M < 2.5M⊙ in the Milky Way and in the Magellanic Clouds indicates smaller 12C/13C ratios (∼ 6 - 18) than the ones predicted from the RGB star models. Measurments of the 13C(p,g)14N reaction cross section performed at the Felsenkeller underground facility in Dresden (Germany) in the energy range 350-700 keV, Being located underground, the γ-ray background is suppressed by more than three orders of magnitude, thus providing a unique environment for low-energy measurements of reaction cross sections.