α-α interaction reexamined in the context of the Sao Paulo potential: possible applications in astrophysics?

Full text: We have analyzed a large set of α-α elastic scattering data for bombarding energies ranging from 0.6 to 29.5 MeV. The complete lack of open reaction channels at these somehow low energies results in a vanishing imaginary part for the optical interaction. This characteristic makes the α-α reaction particularly interesting as the corresponding elastic scattering cross sections and phase shifts become very sensitive to the real part of the interaction. The data were analyzed within the context of the velocity-dependent Sao Paulo potential, which is a successful theoretical model for the description of heavy-ion reactions from sub-barrier to intermediate energies. We have shown that, even in this low energy region, the velocity dependence of the Sao Paulo potential model is a necessary ingredient for describing the data. Despite the reasonable description obtained with the Sao Paulo potential, the analyses indicate the necessity of an additional weak dependence of the interaction on the angular momentum. These important characteristics open the possibility for studying reactions with astrophysical interested. In particular, predictions of the astrophysical S-factor for the 12C(α,γ) reaction will be presented. The understanding of the reaction rate for the α-capture process by a 12C nucleus is a crucial ingredient for predicting the stellar helium burning and the subsequent fate of stars as this reaction determines the ratio of carbon to oxygen towards the end of the Red Giants phase. It is well known that low mass stars evolve to White Dwarfs and this ratio determines the final abundance composition in White Dwarf matter and sets the trigger conditions for type Ia supernova explosions. The carbon-oxygen ratio also dictates the subsequent sequence of burning processes during the final stages of stellar evolution for massive stars. Thus, it has a key role in the determination of the abundance composition in outer shells of the star prior to core collapse, which is the seed for shock-front driven nucleosynthesis. Despite many years of theoretical and experimental efforts, the 12C(α,γ) reaction rate still represents one of the main uncertainties for modeling stellar evolution and explosion with sufficient accuracy. (author)