Search for astrophysically importantNe19levels with a thick-targetF18(p,p)F18measurement

Abstract

The rates of the $^{18}\mathrm{F}(p,\ensuremath{\alpha})^{15}\mathrm{O}$ and $^{18}\mathrm{F}(p,\ensuremath{\gamma})^{19}\mathrm{Ne}$ reactions in astrophysical environments depend on the properties of $^{19}\mathrm{Ne}$ levels above the $^{18}\mathrm{F}+p$ threshold. There are at least eight levels in the mirror nucleus $^{19}\mathrm{F}$ for which analogs have not been observed in $^{19}\mathrm{Ne}$ in the excitation energy range ${E}_{x}=6.4--7.6\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. These levels may significantly enhance the $^{18}\mathrm{F}+p$ reaction rates, and thus we have made a search for these levels by measuring the $^{1}\mathrm{H}(^{18}\mathrm{F},p)^{18}\mathrm{F}$ excitation function over the energy range ${E}_{\mathrm{c.m.}}=0.3--1.3\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. We have identified and measured the properties of a newly observed level at ${E}_{x}=7.420\ifmmode\pm\else\textpm\fi{}0.014\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$, which is most likely the mirror to the ${J}^{\ensuremath{\pi}}={\frac{7}{2}}^{+}\phantom{\rule{0.3em}{0ex}}^{19}\mathrm{F}$ level at $7.56\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. We have additionally found a significant discrepancy with a recent compilation for the properties of a $^{19}\mathrm{Ne}$ state at ${E}_{x}=7.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and set upper limits on the proton widths of missing levels.