Is γ-ray emission from novae affected by interference effects in the F18(p,α)O15 reaction?

The F18(p,α)O15 reaction rate is crucial for constraining model predictions of the γ-ray observable radioisotope F18 produced in novae. The determination of this rate is challenging due to particular features of the level scheme of the compound nucleus, Ne19, which result in interference effects potentially playing a significant role. The dominant uncertainty in this rate arises from interference between Jπ=3/2+ states near the proton threshold (Sp=6.411 MeV) and a broad Jπ=3/2+ state at 665 keV above threshold. This unknown interference term results in up to a factor of 40 uncertainty in the astrophysical S-factor at nova temperatures. Here we report a new measurement of states in this energy region using the F19(He3,t)Ne19 reaction. In stark contrast to previous assumptions we find at least 3 resonances between the proton threshold and Ecm=50 keV, all with different angular distributions. None of these are consistent with Jπ=3/2+ angular distributions. We find that the main uncertainty now arises from the unknown proton width of the 48 keV resonance, not from possible interference effects. Hydrodynamic nova model calculations performed indicate that this unknown width affects F18 production by at least a factor of two in the model considered. © 2013 American Physical Society