New constraints on the F-18(p, alpha)O-15 rate in novae from the (d, p) reaction

Abstract

The degree to which the (p, gamma) and (p, alpha) reactions destroy F-18 at temperatures (1-4) x 10(8) K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide F-18, a target of gamma-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the F-18+p threshold (E-x = 6.411 MeV in Ne-19). To gain further information about these resonances, we used a radioactive F-18 beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in F-19 via the inverse H-2((18)p)F-19 neutron transfer reaction. Neutron spectroscopic factors were measured for states in F-19 in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in Ne-19 were calculated using a Woods-Saxon potential. The results imply significantly lower F-18(p, gamma)Ne-19 and F-18(p, alpha)O-15 reaction rates than reported previously, thereby increasing the prospect of observing the 511 keV annihilation radiation associated with the decay of F-18 in the ashes ejected from novae.