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UBC Theses and Dissertations

Lifetimes of states in 19Ne above the 15O+ alpha threshold Subramanian, Mythili Myths


Astrophysical models that address stellar energy generation and nucleosynthesis require a considerable amount of input from nuclear physics and are very sensitive to the detailed structure of nuclei, both stable and unstable. Radioactive nuclei play a dominant role in several stellar environments such as supernovae, X-ray bursts, novae etc. and nuclear data are important in the interpretation of these phenomena. When carbon, nitrogen and oxygen isotopes are present in substantial quantities in a star of sufficient mass, the fusion of four hydrogen nuclei to form a helium nucleus proceeds via the CNO cycles. Energy release in the CNO cycles is limited by the long lifetimes of 14O and 15O. In explosive stellar scenarios such as X-ray bursts, the energy output is very large, suggesting a breakout from the CNO cycles. 15O(α,γ)19Ne is the first reaction that breaks out of the CNO cycle. Nuclear structure information on high lying states in 19Ne is required to calculate the rate of the 15O(α,γ)19Ne reaction. This work focuses on the study of states in 19Ne above 3.53 MeV. The lifetimes of five states in 19Ne above 3.53 MeV were measured in this work. The states in 19Ne were populated via the 3He(20Ne,α)19Ne reaction at a beam energy of 34 MeV. The lifetimes were measured using the Doppler Shift Attenuation Method. The lifetimes of five states were measured and an upper limit was set on the lifetime of a sixth state. Three of the measurements are the most precise thus far. The lifetimes of the other three states agree with the values of the only other measurement of the lifetimes of these states. An upper limit on the rate of the 15O(α,γ)19Ne reaction was calculated at the 90% confidence level using the measured lifetimes. The contributions to the 15O(α,γ)19Ne reaction rate from several states in 19Ne at different stellar temperatures are discussed.

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