Examination of the role of the O-14(alpha, p)F-17 reaction rate in type-I x-ray bursts

Abstract

The O-14(alpha, p)F-17 reaction is one of the key reactions involved in the breakout from the hot-CNO cycle to the rp-process in type-I x-ray bursts (XRBs). The resonant properties in the compound nucleus Ne-18 have been investigated through resonant elastic scattering of F-17 + p. The radioactive F-17 beam was separated by the Center for Nuclear Study radioactive ion beam separator (CRIB) and bombarded a thick H-2 gas target at 3.6 MeV/nucleon. The recoiling light particles were measured by three Delta E-E silicon telescopes at laboratory angles of theta(lab) approximate to 3 degrees, 10 degrees, and 18 degrees. Five resonances at E-x = 6.15, 6.28, 6.35, 6.85, and 7.05 MeV were observed in the excitation functions, and their spin-parities have been determined based on an R-matrix analysis. In particular, J(pi) = 1(-) was firmly assigned to the 6.15-MeV state which dominates the thermonuclear O-14(alpha, p)F-17 rate below 2 GK. As well, a possible new excited state in Ne-18 was observed at E-x = 6.85 +/- 0.11 MeV with tentative J = 0 assignment. This state could be the analog state of the 6.880 MeV (0(-)) level in the mirror nucleus O-18, or a bandhead state (0(+)) of the six-particle four-hole (6p-4h) band. A new thermonuclear O-14(alpha, p)F-17 rate has been determined, and the astrophysical impact of multiple recent rates has been examined using an XRB model. Contrary to previous expectations, we find only a modest impact on predicted nuclear energy generation rates from using reaction rates differing by up to several orders of magnitude.