Measurement of the O 14 (α,p) F 17 cross section at e c. m.≈2.1-5.3 MeV

Background: The O14(α,p)F17 reaction plays an important role as the trigger reaction for the x-ray burst. Purpose: The direct measurement of O14(α,p)F17 was made for studying the resonant states in Ne18 and determining the reaction rate of O14(α,p)F17 at astrophysical temperatures. Methods: The differential cross section of the O14(α,p)F17 reaction was measured using a 2.5-MeV/u O14 radioactive beam and the thick target method in inverse kinematics. Three sets of ΔE-E Si telescopes were installed and coincidence measurements were performed. We analyzed single-proton decay events using the time-of-flight (TOF) information of the recoiling protons. Results: The excitation function of O14(α,p)F17 was acquired for excitation energies between 7.2 and 10.4 MeV in Ne18 by considering the two channels which decay to the ground state and first excited state of F17. Several new, as well as previously known, states in Ne18 were observed and their resonance parameters were extracted from R-matrix analysis. The contributions of four resonances over the excitation energy range, 7<Ex<8.2MeV, to the O14(α,p)F17 reaction rate were calculated. Conclusions: We observed very strong single-proton decay events, but did not observe strong double-proton decay events as in a previous study by Fu et al. The reaction rates contributed by the 7.35-, 7.58-, and 7.72-MeV states were estimated to be dominant at temperatures T9>2. Among these three states, the 7.35-MeV state was found to enhance the reaction rate by a factor of 10 greater than the other two resonance states.