Investigation of excited states in ${}^{18}$Ne via resonant elastic scattering of ${}^{17}$F+p and its astrophysical implication in the stellar reaction of ${}^{14}$O($\hat{I}\pm$,$p$)${}^{17}$F

Abstract

Properties of proton resonances in ${}^{18}$Ne have been investigated efficiently by utilizing a technique of proton resonant elastic scattering with a ${}^{17}$F radioactive ion (RI) beam and a thick proton target. A 4.22~MeV/nucleon ${}^{17}$F RI beam was produced via a projectile-fragmentation reaction, and subsequently separated by a Radioactive Ion Beam Line in Lanzhou ({\tt RIBLL}). Energy spectra of the recoiled protons were measured by two sets of $\hat{I}”$E-E silicon telescope at center-of-mass scattering angles of $\hat{I}{¸}_{c.m.}$$\approx$175${}^{\circ }$$\pm$5${}^{\circ }$, $\hat{I}{¸}_{c.m.}$$\approx$152${}^{\circ }$$\pm$8${}^{\circ }$, respectively. Several proton resonances in ${}^{18}$Ne were observed, and their resonant parameters have been determined by an $R$-matrix analysis of the differential cross sections in combination with the previous results. The resonant parameters are related to the reaction-rate calculation of the stellar ${}^{14}$O($\hat{I}\pm$,$p$)${}^{17}$F reaction, which was thought to be the breakout reaction from the hot CNO cycles into the $rp$-process in x-ray bursters. Here, $J^{\ddot{I}}€$=(3${}^{-}$, 2${}^{-}$) are tentatively assigned to the 6.15-MeV state which was thought the key 1${}^{-}$ state previously. In addition, a doublet structure at 7.05 MeV are tentatively identified, and its contribution to the resonant reaction rate of ${}^{14}$O($\hat{I}\pm$,$p$)${}^{17}$F could be enhanced by at least factors of about 4$\sim$6 in comparison with the previous estimation involving only a singlet. The present calculated resonant rates are much larger than those previous values, and it may imply that this breakout reaction could play a crucial role under x-ray bursters conditions.

8 figures, 2 tables