New Limits for the 18F(p, α)15O Rate in Novae

The degree to which the ( p , γ ) and ( p , α ) reactions destroy 18 F at temperatures ∼ 1 − 4 × 10 8  K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide 18 F, a target of gamma ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the 18 F+p threshold ( E x = 6.411  MeV in 19 Ne). To gain further information about these resonances, we have used the d( 18 F , p ) 19 F neutron transfer reaction to selectively populate corresponding mirror states in 19 F. The results would suggest 18 F( p , γ ) 19 Ne and 18 F( p , α ) 15 O reaction rates that are 2-3 times lower than reported previously.