Spin-parities of subthreshold resonances in the F18(p,α)O15 reaction

Abstract

The $^{18}\mathrm{F}(p,\ensuremath{\alpha})^{15}\mathrm{O}$ reaction is key to determining the $^{18}\mathrm{F}$ abundance in classical novae. However, the cross section for this reaction has large uncertainties at low energies largely caused by interference effects. Here, we resolve a longstanding issue with unknown spin-parities of subthreshold states in $^{19}\mathrm{Ne}$ that reduces these uncertainties. The $^{20}\mathrm{Ne}(^{3}\mathrm{He},^{4}\mathrm{He})^{19}\mathrm{Ne}$ neutron pick-up reaction was used to populate $^{19}\mathrm{Ne}$ excited states, focusing on the energy region of astrophysical interest $(\ensuremath{\approx}6--7 \mathrm{MeV})$. The experiment was performed at the Triangle Universities Nuclear Laboratory using the high resolution Enge split-pole magnetic spectrograph. Spins and parities were found for states in the astrophysical energy range. In particular, the state at 6.133 MeV $({E}_{r}^{\text{c.m.}}=\ensuremath{-}277 \mathrm{keV})$ was found to have spin and parity of $3/{2}^{+}$ and we confirm the existence of an unresolved doublet close to 6.288 MeV $({E}_{r}^{\text{c.m.}}=\ensuremath{-}120 \mathrm{keV})$ with ${J}^{\ensuremath{\pi}}=1/{2}^{+}$ and a high-spin state. Using these results, we demonstrate a significant factor of two decrease in the reaction rate uncertainties at nova temperatures.