Energy, strength, and α width measurements of Ec.m.=1323 and 1487 keV resonances in 15N( α , γ )19F

The N-15(alpha,gamma)F-19 reaction produces F-19 in asymptotic giant branch (AGB) stars, where the low energy tails of two resonances at E-c.m.=1323 +/- 2 and 1487 +/- 1.7 keV are estimated to contribute about 30% of the total reaction rate in these environments. However, recent measurements have shown discrepancies in the energies, the strengths, and the corresponding alpha widths of these two resonances, resulting in an increase in the systematic uncertainty of the extrapolated cross section to helium burning energies. With this motivation, we have undertaken new measurements of the N-15(alpha,gamma)F-19 at the University of Notre Dame Nuclear Science Laboratory. The setup consisted of an alpha particle beam impinged on a solid (TiN)-N-15 target with gamma-ray spectroscopy accomplished using a high purity germanium detector. Using the Doppler corrected gamma-ray energies, we confirmed the lower resonance energy to be 1321.6 +/- 0.6 keV and found a value for the higher one of 1479.4 +/- 0.6 keV that is more consistent with those found from previous elastic scattering studies. We found that the resonance strengths for both were consistent with most values found in the literature, but a larger alpha width has been recommended for the E-c.m.=1487 keV resonance. The larger alpha width suggests a reaction rate increase of about 15% at temperatures T<0.1 GK relevant to low mass AGB stars. The impact of the increased reaction rate requires further investigations.