Spectroscopy of Ne 19 for the thermonuclear O 15 (alfa,gamma) Ne 19 and F 18 (pi,alfa) O 15 reaction rates

Abstract

Uncertainties in the thermonuclear rates of the O15(a,¿)19Ne and 18F(p,a)15O reactions affect model predictions of light curves from type I x-ray bursts and the amount of the observable radioisotope F18 produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of Ne19 over Ex=4.0-5.1 and 6.1-7.3 MeV using the F19(He3,t)Ne19 reaction. We find the Jp 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 Ne19 around the proton threshold before a reliable 18F(p,a)15O rate for nova models can be determined.