An investigation of the d(18Ne,19Ne*)p reaction and its astrophysical relevance

Abstract

The reaction 15 O(alpha; gamma) 19 Ne is one of the potential break­out reactions from the Hot CNO cycle to the rp­process. As such, it may play an important role in nuclear astrophysics for the understanding of energy generation rates and the synthesis of proton­rich nuclei in sites of explosive hydrogen burning, such as novae and X­ray bursters. Experiments were performed at the radioactive ion beam facility, at Louvain­la­Neuve, Belgium, to test the validity of measuring indirectly the 15 O(alpha; gamma) 19 Ne reaction rate. The method utilised was the population of ex­ cited states in 19 Ne and the observation of their ff­decay. Information on the alpha branching ratios of the states of astrophysical interest, just above the alpha­ threshold, allows the reaction rate to be calculated, provided other resonance properties, i.e. T , ER and J , are known. Excited states in 19 Ne were populated via an inverse 18 Ne(d,p) reac­ tion on a deuterated polyethylene target. The reaction and decay products were measured in an experimental set up that comprised three silicon strip detector arrays, with a total of 320 detector elements. Two experiments were performed at E lab = 44.1 MeV and E lab = 54.3 MeV. The recoiling protons tagged the populated state and the detection of a coincident ff­particle and heavy residue pair identified its decay. Branching ratios for several states in 19 Ne were determined, showing the viability of this experimental approach. Optical model parameters were de­ termined from 18 Ne elastic scattering on deuterons. DWBA calculations were performed and compared with experimental angular distributions to yield spectroscopic factors. The results were comparable with a previous meas­ urement using a stable beam, despite the significantly lower beam intensity, and indicated that, provided the necessary beam intensity was available, this method would allow the measurement of the alpha branching ratio of the reson­ ance of most astrophysical interest at 504 keV and thus the determination of the 15 O(alpha; gamma) 19 Ne reaction rate.