Aspects of Nuclear Phenomena Under Explosive Astrophysical Conditions



The breakout of the hot CNO cycle and the onset of the rapid-proton process are of significant importance to our understanding of the nucleosynthesis of proton-rich nuclei in our universe. In particular 15O(α,γ)19Ne and 21Na(p,γ)22Mg are both thought to be key reactions for these processes under explosive astrophysical conditions. In this work, an experiment has been carried out at Louvain-la-Neuve, Belgium, in order to test the feasibility of a measurement of the lifetime of the 4.033 MeV state in 19Ne, which is considered extremely important for the 15O(α,γ)19Ne reaction. Also, an elastic-scattering experiment was performed using a newly-developed 21Na beam at the ISAC post-accelerated radioactive beam facility in Vancouver, Canada. The experiment represents the first scientific result achieved with this facility. A centre-of-mass energy range of ≈ 0.4-1.5 MeV was investigated using a thick-target scan technique utilising polyethylene ([CH2]n) foils. Data were collected using a silicon charged-particle detector array, enabling the identification of elastic and inelastic resonances in the 21Na+p system. Monte-Carlo simulations were used to estimate the experimental resolution effects present in the experiment. These results were then incor- porated into an analysis of the data using a single-channel l = 0 R-matrix code. An analysis of the data enabled the identification of four states in 22Mg, one of which was previously unobserved. Resonance energies and widths were estimated for each of these states. A comparison of the results with states in the T=1 analogue system was made. The effect a detailed knowledge of these resonances would have on the 21Na(p,γ)22Mg rate under extreme high temperature conditions was also investigated.

Author: Erikson, L.