A Study of 19Ne Resonances and their Astrophysical Implication for the Detection of Novae

Classical novae are the most common astrophysical thermonuclear explosion and are thought to contribute noticeably to the galactic chemical evolution. As one of the few environments that can be modelled primarily from experimental nuclear data, observations of isotopic abundances would provide a direct test for current hydrodynamic codes. Gamma rays are the only such radiation that can be observed to trace the nucleosynthesis of isotopes directly. Fluorine-18 produced in the runaway is the strongest γ-ray source immediately after the outburst, although reaction rates must be constrained further to predict its intensity and therefore detectability. The 18F(p,α)15O reaction remains the largest uncertainty in constraining these rates as key nuclear state parameters in the compound nucleus, 19Ne, are still not known despite considerable experimental effort. To resolve this, the most important levels close to the proton threshold were populated using the charge exchange reaction 19F(3He,t)19Ne at IPN, Orsay. A Split-pole spectrometer measured the tritons and identified the states of interest, whilst a highly segmented silicon array detected alpha-particle and proton decays from 19Ne over a large angular range and at a high angular resolution. The resonance parameters, extracted from the experimental results, provide evidence for a postulated broad state and produce a spin-parity result for the important -122 keV subthreshold state in direct contradiction to previous measurements of the nucleus. The results, in addition to other recent studies, provided input parameters for a comprehensive set of theoretical R-matrix calculations that have realistically modelled the remaining uncertainty in the reaction rate. The newly proposed rate is discussed, along with implications for future studies of the destruction reaction, both direct and indirect, which are necessary in providing an answer to the γ-ray detectability of classical novae.