The 13C(α, n)16O reaction is the main neutron source for the s-process in low mass AGB stars. Although several direct measurements have been performed, no dataset reaches the Gamow window (140-250 keV) due to the the exponential drop of the cross section σ(E) with decreasing energy. The reaction rate becomes so low that the strong cosmic background would become predominant.
A recent new measurement was carried out in deep underground laboratories of Laboratori Nazionali del Gran Sasso (LNGS) in the framework of the LUNA experiment.
In order to measure the 13C(α,n)16O cross section at low energies, a multiple effort has been performed, namely 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 (100-200 μA). Thanks to these accuracies, the 13C(α, n)16O cross section was measured in the center of mass energy range 230<Ecm<305 keV with an overall uncertainty of maximum 20%. This allowed to constrain the reaction rate at T=0.1 GK at 10% uncertainty.