Destruction of 18F via 18F(p,α) 15O burning through the Ec.m.=665 keV resonance

D. W. Bardayan, ORNL Physics Division
J. C. Blackmon, ORNL Physics Division
W. Bradfield-Smith, Yale University
C. R. Brune, The University of North Carolina at Chapel Hill
A. E. Champagne, The University of North Carolina at Chapel Hill
T. Davinson, The University of Edinburgh
B. A. Johnson, Tennessee Technological University
R. L. Kozub, Tennessee Technological University
C. S. Lee, Chung-Ang University
R. Lewis, Yale University
P. D. Parker, Yale University
A. C. Shotter, The University of Edinburgh
M. S. Smith, ORNL Physics Division
D. W. Visser, Yale University
P. J. Woods, The University of Edinburgh


Knowledge of the astrophysical rate of the 18F(p,α)15O reaction is important for understanding the γ-ray emission expected from novae and heavy-element production in x-ray bursts. The rate of this reaction is dominated at temperatures above ∼0.4 GK by a resonance near 7.08 MeV excitation energy in 19Ne. The 18F(p,α)15O rate has been uncertain in part because of disagreements among previous measurements concerning the resonance strength and excitation energy of this state. To resolve these uncertainties, we have made simultaneous measurements of the 1H(18F,p)18F and 1H(18F,α)15O excitation functions using a radioactive 18F beam at the ORNL Holifield Radioactive Ion Beam Facility. A simultaneous fit of the data sets has been performed, and the best fit was obtained with a center-of-mass resonance energy of 664.7±1.6 keV (Ex = 7076±2 keV), a total width of 39.0±1.6 keV, a proton branching ratio of Γp/Γ = 0.39±0.02, and a resonance strength of ωγ= 6.2±0.3 keV.