Spectroscopy of 19Ne for the thermonuclear 15O(alpha,gamma)19Ne and 18extF(p,alpha)15O reaction rates

Abstract

Uncertainties in the thermonuclear rates of the 15O(alpha,gamma)19Ne and 18F(p,alpha)15O reactions affect model predictions of light curves from type I x-ray bursts and the amount of the observable radioisotope 18F produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of 19Ne over Ex = 4.0 - 5.1 and 6.1 - 7.3 MeV using the 19F( 3He, t )19Ne 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 levelsmay exist near the 6.86-MeV state. Higher resolution experiments are urgently needed to further clarify the structure of 19Ne around the proton threshold before a reliable 18F(p,alpha)15O rate for nova models can be determined.