New analysis of p + F-19 reactions at low energies and the spectroscopy of natural-parity states in Ne-20

Low-spin natural-parity states in Ne-20 at excitation energies larger than the proton separation energy can be fruitfully explored by analyzing the behavior of the( 19)F(p, alpha(0)) O-16 and F-19(p, alpha(pi))O-16 reactions. Previous analyses were affected by the presence of fragmentary data, often limited to small bombarding energy ranges and to just one reaction channel, preventing any firm conclusion on the spectroscopy of such states. We propose a critical analysis of all data sets published in the literature, especially concerning angular distribution and cross-section data of the F-19(p, alpha(0))O-16 and F-19(p, alpha(pi))O-16 reactions at low bombarding energies (E-p approximate to 0.2-10 MeV). For the first time, we perform a comprehensive R-matrix analysis of all such data, including also p + F-19 elastic scattering data to better determine the partial widths associated to each decay channel. The obtained results help to remove uncertainties on several J(pi) assignments for known states and point out the possible non-negligible role played by low-energy resonances in the determination of the F-19(p, alpha(pi))O-16 reaction rate at temperatures relevant for Asimptotic Giant Branch (AGB) stars.