The determination of the astrophysical S-factor of the direct ¹⁸O(p,$\gamma$)¹⁹F capture by the ANC method

Abstract.

The depletion of ¹⁸O via the $(\mathrm{p},\gamma)$ capture competes with the $(\mathrm{p}, \alpha)$ capture during the CNO cycles in AGB stars. Despite the fact that the $(\mathrm{p}, \alpha)$ capture is dominant, the $(\mathrm{p}, \gamma)$ can play an important role in mixing stages of the AGB star evolution. Here, we attempt to determine the astrophysical S-factor of the direct part of the ¹⁸O(p,$\gamma$)¹⁹F capture by the indirect method of asymptotic normalization coefficients (ANC). We measure the differential cross section of the transfer reaction ¹⁸O(³He, d)¹⁹F at a ³He energy of 24.6 MeV. The measurement was performed on the cyclotron of the CANAM infrastructure of NPI in Řež, Czech Republic, with the gas target consisting of the high-purity ¹⁸O (99.9%). The reaction products were measured by eight $\Delta E$-E telescopes composed of thin and thick silicon surface-barrier detectors. The parameters of the optical model for the input channel were deduced by means of the code ECIS and the analysis of transfer reactions to 12 levels of the ¹⁹F nucleus up to 8.014 MeV was made by the code FRESCO. The deduced ANCs were then used to specify the direct contribution to the ¹⁸O(p,$\gamma$)¹⁹F capture process and were compared with the mutually different results of two works.