Determination of α-widths in 19F relevant to fluorine nucleosynthesis

Abstract

Abstract Nucleosynthesis of fluorine in the context of helium burning occurs through the 15 N(α,γ) 19 F reaction. At temperatures where fluorine formation takes place in most astrophysical models, the narrow resonance associated with the 4.378 MeV level of 19 F is expected to dominate the reaction rate, but its strength is not known. We used a 15 N confined gas target to study this level by means of the transfer reaction 15 N 7 Li,t) 19 F at 28 MeV. Reaction products products were analysed with a split pole magnetic spectrometer and the angular distributions for the first 16 levels of 19 F were extracted. These distributions are fairly well reproduced by FR-DWBA calculations in the framework of an α-cluster transfer model with a compound-nucleus contribution obtained by Hauser-Feshbach calculations. α-spectroscopic factors were deduced and, for unbound levels, the α-widths were determined and compared with the existing direct measurements. The α-width of the level of astrophysical interest ( E x = 4.378 MeV) was found to be Γ α = 1.5 × 10 −9 eV, a value 60 times smaller than the commonly used one. The astrophysical consequences for 19 F production in AGB stars are discussed.