Spectroscopy of Ne-19 for the thermonuclear O-15(alpha, gamma)Ne-19 and F-18(p, alpha)O-15 reaction rates
Résumé
Uncertainties in the thermonuclear rates of the O-15(alpha, gamma) Ne-19 and F-18(p, alpha) O-15 reactions affect model predictions of light curves from type I x-ray bursts and the amount of the observable radioisotope F-18 produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of Ne-19 over E-x = 4.0 - 5.1 and 6.1-7.3 MeV using the F-19(He-3, t) Ne-19 reaction. We find the J(pi) values of the 4.14- and 4.20-MeV levels to be consistent with 9/2(-) and 7/2(-), respectively, in contrast to previous assumptions. We confirm the recently observed triplet of states around 6.4 MeV and find evidence that the state at 6.29 MeV, just below the proton threshold, is either broad or a doublet. Our data also suggest that predicted but yet unobserved levels may exist near the 6.86-MeV state. Higher resolution experiments are urgently needed to further clarify the structure of Ne-19 around the proton threshold before a reliable F-18(p, alpha) O-15 rate for nova models can be determined.