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

The degree to which the (p,γ) and (p,α) reactions destroy ¹⁸F at temperatures (1-4)×10⁸ K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide ¹⁸F, a target of γ-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the ¹⁸F+p threshold (E_x=6.411 MeV in ¹⁹Ne). To gain further information about these resonances, we used a radioactive ¹⁸F beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in ¹⁹F via the inverse ²H(¹⁸F,p)¹⁹F neutron transfer reaction. Neutron spectroscopic factors were measured for states in ¹⁹F in the excitation energy range 0–9 MeV. Widths for corresponding proton resonances in ¹⁹Ne were calculated using a Woods-Saxon potential. The results imply significantly lower ¹⁸F(p,γ)¹⁹Ne and ¹⁸F(p,α)¹⁵O reaction rates than reported previously, thereby increasing the prospect of observing the 511 keV annihilation radiation associated with the decay of ¹⁸F in the ashes ejected from novae.