Measurement of 1323 and 1487 keV resonances inN15(α,γ)F19with the recoil separator ERNA

Background: The origin of fluorine is a widely debated issue. Nevertheless, the $^{15}\mathrm{N}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{F}$ reaction is a common feature among the various production channels so far proposed. Its reaction rate at relevant temperatures is determined by a number of narrow resonances together with the direct capture and the tails of the two broad resonances at ${E}_{\mathrm{c}.\mathrm{m}.}=1323$ and 1487 keV.Purpose: The broad resonances widths, ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$ and ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}$, have to be measured with adequate precision in order to better determine their contribution to the $^{15}\mathrm{N}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{F}$ stellar reaction rate.Methods: Measurement through the direct detection of the $^{19}\mathrm{F}$ recoil ions with the European Recoil separator for Nuclear Astrophysics (ERNA) were performed. The reaction was initiated by a $^{15}\mathrm{N}$ beam impinging onto a $^{4}\mathrm{He}$ windowless gas target. The observed yield of the resonances at ${E}_{\mathrm{c}.\mathrm{m}.}=1323$ and 1487 keV is used to determine their widths in the $\ensuremath{\alpha}$ and $\ensuremath{\gamma}$ channels.Results: We show that a direct measurement of the cross section of the $^{15}\mathrm{N}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{F}$ reaction can be successfully obtained with the recoil separator ERNA, and the widths ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$ and ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}$ of the two broad resonances have been determined. While a fair agreement is found with earlier determination of the widths of the 1487 keV resonance, a significant difference is found for the 1323 keV resonance ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\alpha}}$.Conclusions: The revision of the widths of the two more relevant broad resonances in the $^{15}\mathrm{N}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{F}$ reaction presented in this work is the first step toward a more firm determination of the reaction rate. At present, the residual uncertainty at the temperatures of the $^{19}\mathrm{F}$ stellar nucleosynthesis is dominated by the uncertainties affecting the direct capture component and the 364 keV narrow resonance, both so far investigated only through indirect experiments.