Study of interference effects in the 18 F ( p , α ) 15 O reaction

The 18F(p,α)15O reaction plays a crucial role in understanding γ-ray emission from novae. Because of the importance of understanding the 18F + p reactions, a number of studies of the A=19 isobars have been made using stable and exotic beams. The int erf rence effects among Jπ = 2 + resonances in the 18F + p system, however, have never been measured, but they can chan ge the S-factor by a factor of 20 at nova energies. R-matrix calculations indicate that the cross sections above theEc.m. = 665 keV resonance are sensitive to the interference betwee n th Ec.m. = 8, 38, and 665 keV resonances. In order to study the interfere nc ffects, an excitation function for the 1H(18F,α)15O reaction has been measured in the energy range of Ec.m. = 663-877 keV using radioactive18F beams at the Holifield Radioactive Ion Beam Facility. By mea suring the 18F(p,α)15O cross section off resonance and comparing the cross sectio n wi h theoretical calculations, we provide the first experimental constraints on th e interference of2 + resonances.