Friday

Direct observation of gamma-ray emission from the decay of 18F ejected in classical nova outbursts remains a major focus of the nuclear astrophysics community. However, modeling the abundance of ejected 18F, and thus the predicted detectability distance of a gamma-ray signal near 511 keV emitted from these transient thermonuclear episodes, is hampered by significant uncertainties in our knowledge of the key 18F(p,alpha) reaction rate. We analyze uncertainties in the most recent nuclear physics experimental results employed to calculate the 18F(p,alpha) reaction rate. Our goal is to determine which uncertainties have the most profound influence on the predicted abundance of 18F ejected from novae, in order to guide future experimental works. We calculated a wide range of 18F(p,alpha) reaction rates using R-Matrix formalism, allowing us to take into account all interference effects. Using a selection of 16 evenly-spaced rates over the full range, we performed 16 new hydrodynamic nova simulations. We performed one of the most thorough theoretical studies of the impact of the 18F(p,alpha) reaction in classical novae to date. The 18F(p,alpha) rate remains highly uncertain at nova temperatures, resulting in a factor ∼10 uncertainty in the predicted abundance of 18F ejected from nova explosions. We also found that the abundance of 18F may be strongly correlated with that of 19F. Despite numerous nuclear physics uncertainties affecting the 18F(p,alpha) reaction rate, which are dominated by unknown interference signs between 1/2+ and 3/2+ resonances, future experimental work should focus on firmly and precisely determining the directly measurable quantum properties of the subthreshold states in the compound nucleus 19Ne near 6.13 and 6.29 MeV.