Examination of the role of theO14(α,p)F17reaction rate in type-I x-ray bursts

Abstract

The $^{14}\mathrm{O}(\ensuremath{\alpha},p)^{17}\mathrm{F}$ reaction is one of the key reactions involved in the breakout from the hot-CNO cycle to the rp-process in type-I x-ray bursts (XRBs). The resonant properties in the compound nucleus $^{18}\mathrm{Ne}$ have been investigated through resonant elastic scattering of $^{17}\mathrm{F}+p$. The radioactive $^{17}\mathrm{F}$ beam was separated by the Center for Nuclear Study radioactive ion beam separator (CRIB) and bombarded a thick ${\mathrm{H}}_{2}$ gas target at 3.6 MeV/nucleon. The recoiling light particles were measured by three $\ensuremath{\Delta}E\text{\ensuremath{-}}E$ silicon telescopes at laboratory angles of ${\ensuremath{\theta}}_{\mathrm{lab}}\ensuremath{\approx}3{}^{\ensuremath{\circ}},10{}^{\ensuremath{\circ}}$, and $18{}^{\ensuremath{\circ}}$. Five resonances at ${E}_{x}=6.15$, 6.28, 6.35, 6.85, and 7.05 MeV were observed in the excitation functions, and their spin-parities have been determined based on an $R$-matrix analysis. In particular, ${J}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$ was firmly assigned to the 6.15-MeV state which dominates the thermonuclear $^{14}\mathrm{O}(\ensuremath{\alpha},p)^{17}\mathrm{F}$ rate below 2 GK. As well, a possible new excited state in $^{18}\mathrm{Ne}$ was observed at ${E}_{x}=6.85\ifmmode\pm\else\textpm\fi{}0.11$ MeV with tentative $J=0$ assignment. This state could be the analog state of the 6.880 MeV $(0{}^{\ensuremath{-}})$ level in the mirror nucleus $^{18}\mathrm{O}$, or a bandhead state $(0{}^{+})$ of the six-particle four-hole (6p-4h) band. A new thermonuclear $^{14}\mathrm{O}(\ensuremath{\alpha},p)^{17}\mathrm{F}$ rate has been determined, and the astrophysical impact of multiple recent rates has been examined using an XRB model. Contrary to previous expectations, we find only a modest impact on predicted nuclear energy generation rates from using reaction rates differing by up to several orders of magnitude.