Measurement of 19Ne(p,γ)20Na in relation to explosive stellar phenomena.

Abstract

The 19Ne(p,γ)20Na reaction is thought to play a significant role in the nucleosynthesis of explosive stellar phenomena, with a single narrow resonant state located above the proton emission threshold in 20Na thought to dominate the stellar reaction rate at oxygen-neon (ONe) novae and X-ray burst temperatures. In this thesis, the properties of this resonance of astrophysical interest, the subject of experimental and theoretical debate for nearly thirty years, have been measured directly for the first time, using the DRAGON recoil separator to investigate an energy region approximately 10 keV higher than previous direct measurements. The resonance of astrophysical interest was populated by bombarding a windowless hydrogen gas target with a beam of 19Ne, produced by the ISAC facility at TRIUMF National Laboratory. The resulting 20Na recoils were transported to the focal plane of DRAGON, where they were stopped and detected, whilst the radiative capture γ-rays were detected in a BGO array surrounding the target, allowing both the resonance energy and resonance strength to be measured. Doing so made it possible to re-evaluate the stellar reaction rate, relative to the results of recent theoretical and indirect studies of the same reaction. This resonant state of interest has also been measured indirectly via a study of the 19F(d,p)20F reaction, performed primarily to commission the TIARA array at Texas A&M University. The silicon array, coupled to the MDM-2 magnetic spectrometer, Oxford focal plane detector and HPGe clover detectors for the first time, was used to measure the highest energy particle-γ coincidence dataset investigating the structure of 20F. This allowed a decay scheme as well as angular distributions to be produced. The TWOFNR reaction code was used to produce theoretical angular distributions which were used to determine spectroscopic factors, the absolute values of which were then compared with the results of historical studies of the 19F(d,p)20F reaction. By commissioning the new experimental set-up, it can now be used to perform indirect measurements of astrophysical reactions, the direct study of which is beyond contemporary technical capabilities.