Properties of resonant states in 18Ne relevant to key 14O(alpha,p)17F breakout reaction in type I x-ray bursts

Abstract

The ${}^{14}$O($\hat{I}\pm$,$p$)${}^{17}$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. The resonant properties in the compound nucleus ${}^{18}$Ne have been investigated through resonant elastic scattering of ${}^{17}$F+$p$. The radioactive ${}^{17}$F beam was separated by the CNS Radioactive Ion Beam separator (CRIB) and bombarded a thick H${}_2$ gas target at 3.6 MeV/nucleon. The recoiling light particles were measured by using three $\hat{I}”$E-E silicon telescopes at laboratory angles of $\hat{I}¸$${}_{lab}$$\approx$3${}^{\circ }$, 10${}^{\circ }$ and 18${}^{\circ }$, respectively. Five resonances at $E_x$=6.15, 6.28, 6.35, 6.85, and 7.05 MeV were observed in the excitation functions. Based on an $R$-matrix analysis, $J^{\ddot{I}}€$=1${}^{-}$ was firmly assigned to the 6.15-MeV state. This state dominates the thermonuclear ${}^{14}$O($\hat{I}\pm$,$p$)${}^{17}$F rate below 1 GK. We have also confirmed the existence and spin-parities of three states between 6.1 and 6.4 MeV. As well, a possible new excited state in ${}^{18}$Ne was observed at $E_x$=6.85$\pm$0.11 MeV and tentatively assigned as $J$=0. This state could be the analog state of the 6.880 MeV (0${}^{-}$) level in the mirror nucleus ${}^{18}$O, or a bandhead state (0${}^{+}$) of the six-particle four-hole (6$p$-4$h$) band. A new thermonuclear rate of the ${}^{14}$O($\hat{I}\pm$,$p$)${}^{17}$F reaction has been determined, and its astrophysical impact has been examined within the framework of one-zone x-ray burst postprocessing calculations.