Investigation of the s-process neutron source 22Ne+alpha Public Deposited

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  • March 21, 2019
  • Longland, Richard Leigh
    • Affiliation: College of Arts and Sciences, Department of Physics and Astronomy
  • Neutron capture processes are associated with the production of most elements heavier than iron. The s-process is one such scenario for this nucleosynthesis, in which neutrons are captured at a slower rate than beta-decay occurs, resulting in the enrichment of nuclei along the nuclear valley of stability. An important reaction that can produce these neutrons is 22Ne(alpha n)25Mg. Uncertainties in the rate of this reaction and its competing 22Ne(alpha gamma)26Mg reaction hinder our understanding of nucleosynthesis in AGB stars and massive stars, the favoured sites for the s-process. Without improved nuclear physics input, constraints on the structure of these stars cannot be reliably applied from observational evidence. In the present study, the 22Ne+alpha reactions were investigated. A nuclear resonance fluorescence experiment was performed on the compound 26Mg nucleus. The experiment used linearly polarised photons to excite 26Mg and the emitted gamma-rays were analysed to find the properties of excited states, thus improving our understanding of the resonance properties for the 22Ne+alpha reactions. The findings of the experiment were incorporated into a re-evaluation of literature data, in which rates and their associated uncertainties were calculated with a novel Monte Carlo method. Rates on the order of 10 times lower than the literature values were obtained for the 22Ne(alpha gamma)26Mg reaction, while the 22Ne(alpha n)25Mg was in agreement with the most recent results. The uncertainties of both reaction rates were reduced by an order of magnitude. In order to further clarify the current literature data, direct measurements of both reactions should be performed in the future. In the present work, a novel method for determining the resonance strength for the Elabr=479 keV resonance in 22Ne(p,gamma)23Na was developed. This new strength of wg = 0.524 (51) eV significantly reduces 22Ne target stoichiometry uncertainty, which was one of the largest sources of uncertainty in direct 22Ne+alpha cross section measurements.
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  • Iliadis, Christian
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  • University of North Carolina at Chapel Hill
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