Destruction of18Fvia18F(p,α)15Oburning through theEc.m.=665keV resonance

Abstract

Knowledge of the astrophysical rate of the ${}^{18}\mathrm{F}(p,\ensuremath{\alpha}{)}^{15}\mathrm{O}\mathrm{}$ reaction is important for understanding the \ensuremath{\gamma}-ray emission expected from novae and heavy-element production in x-ray bursts. The rate of this reaction is dominated at temperatures above $\ensuremath{\sim}0.4$ GK by a resonance near 7.08 MeV excitation energy in ${}^{19}\mathrm{Ne}.$ The ${}^{18}\mathrm{F}(p,\ensuremath{\alpha}{)}^{15}\mathrm{O}$ rate has been uncertain in part because of disagreements among previous measurements concerning the resonance strength and excitation energy of this state. To resolve these uncertainties, we have made simultaneous measurements of the ${}^{1}\mathrm{H}{(}^{18}\mathrm{F}{,p)}^{18}\mathrm{F}$ and ${}^{1}\mathrm{H}{(}^{18}\mathrm{F},\ensuremath{\alpha}{)}^{15}\mathrm{O}$ excitation functions using a radioactive ${}^{18}\mathrm{F}$ beam at the ORNL Holifield Radioactive Ion Beam Facility. A simultaneous fit of the data sets has been performed, and the best fit was obtained with a center-of-mass resonance energy of $664.7\ifmmode\pm\else\textpm\fi{}1.6$ keV ${(E}_{x}=7076\ifmmode\pm\else\textpm\fi{}2$ keV), a total width of $39.0\ifmmode\pm\else\textpm\fi{}1.6$ keV, a proton branching ratio of ${\ensuremath{\Gamma}}_{p}/\ensuremath{\Gamma}=0.39\ifmmode\pm\else\textpm\fi{}0.02,$ and a resonance strength of $\ensuremath{\omega}\ensuremath{\gamma}=6.2\ifmmode\pm\else\textpm\fi{}0.3$ keV.