Sub-threshold states in ${}^{19}$Ne relevant to ${}^{18}$F(p,$\alpha$)${}^{15}$O

Abstract

Classical novae result from thermonuclear explosions producing several $\gamma$-ray emitters which are prime targets for satellites observing in the MeV range. The early 511 keV gamma-ray emission depends critically on the ${}^{18}$F(p,$\alpha$)${}^{15}$O reaction rate which, despite many experimental and theoretical efforts, still remains uncertain. One of the main uncertainties in the ${}^{18}$F(p,$\alpha$)${}^{15}$O reaction rate is the contribution in the Gamow window of interference between sub-threshold ${}^{19}$Ne states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states. States in the ${}^{19}$Ne compound nucleus were studied at the Tandem-ALTO facility using the ${}^{19}$F(${}^3$He,t)${}^{19}$Ne charge exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or $\alpha$-particles from unbound ${}^{19}$Ne states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established. The coincidence yield at $E_x$ = 6.29 MeV was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high spin and low spin components. Evidence for a broad, low spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. R-matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold. The levels schemes of ${}^{19}$Ne and ${}^{19}$F are still not sufficiently well known and further studies of the analogue assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.

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Cited by in corpus (2)

• The impact of metallicity on nova populations
• Spin-parities of sub-threshold resonances in the ${}^{18}$F(p, $\alpha$)${}^{15}$O reaction