Final results on the 13C(α,n)16O cross section at low energies at LUNA

Abstract

It is well established that the 13C(α, n)16O reaction (Q=2.215 MeV) is the major neutron source feeding the s-process in low mass (1−3M⊙) Asymptotic Giant Branch (AGB) stars. In the last decades, several measurements have been performed. Nevertheless, no dataset reaches the Gamow window (140 keV <Ec.m.<250 keV). This is due to the exponential drop of the cross section σ(E) with decreasing energy. The consequence is that the reaction rate becomes so low that the cosmic background becomes predominant in surface laboratories. A recent measurement was carried out in deep underground laboratory of Laboratori Nazionali del Gran Sasso (LNGS) in the framework of the LUNA experiment. To measure the 13C(α, n)16O cross section at low energies, a multiple effort has been performed to suppress the background in the setup, to maximise the detector efficiency and to keep under control the target modification under an intense stable beam provided by the LUNA accelerator (<I>= 200 µA). Thanks to these accuracies, the 13C(α, n)16O cross section was measured in the center of mass energy range 230 keV <Ecm<305 keV with a maximum 20% overall uncertainty. This allowed to constrain the reaction rate at T=0.1 GK at 15% uncertainty and to lead the way for new possible astrophysical consequences.