A confirmative spin-parity assignment for the key 6.15 MeV state in ${}^{18}$Ne of astrophysical importance

Abstract

Proton resonant states in ${}^{18}$Ne have been investigated by the resonant elastic scattering of ${}^{17}$F+$p$. The ${}^{17}$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 recoiled light particles were measured by using three sets of $\hat{I}”$E-E Si telescope at scattering angles of $\hat{I}¸$${}_{lab}$$\approx 3^{\circ }$, 10${}^{\circ }$ and 18${}^{\circ }$, respectively. Four resonances, {\it i.e.}, at $E_x$=6.15, 6.30, 6.85, and 7.05 MeV, were observed clearly. By $R$-matrix analysis of the excitation functions, $J^{\ddot{I}}€$=1${}^{-}$ was firmly assigned to the 6.15 MeV state which is a key state in calculating the reaction rate of ${}^{14}$O($\hat{I}\pm$,$p$)${}^{17}$F reaction. This reaction was thought to be one of the most probable key reactions for the breakout from the hot-CNO cycle to the $rp$-process in type I x-ray bursts In addition, a new excited state observed at $E_x$=6.85 MeV was tentatively assigned as 0${}^{-}$, which could be the analog state of 6.880 MeV, 0${}^{-}$ in mirror ${}^{18}$O.

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