Breakout Reactions from the CNO-cycle

Louis J Jisonna

doi:https://doi.org/10.21985/N2H442

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Breakout Reactions from the CNO-cycle

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Breakout reactions from the CNO cycles leading into the rp-process in explosive stellar hydrogen burning environments have been studied using the Argonne Tandem Linac Accelerator System (ATLAS). Earlier work is reported and summarized with an introduction to the beam, target and detector development in the nuclear astrophysics group at Argonne National Laboratory. The 18Ne(alpha,p)21Na reaction has been studied via the time inverse reaction p(21Na,alpha)18Ne using a 5 × 10-5 particle nanoamp 21Na beam produced at the ATLAS in-flight facility via the p(21Ne,n)21Na reaction. Cross sections were obtained at five energies covering the region between 9.4 < Ex < 9.9 MeV in the compound nucleus 22Mg, and compared with previous measurements. The 19Ne(p,gamma)20Na reaction was also studied by populating proton unbound states via the 3He(20Ne,t)20Na* reaction. We have observed for the first time evidence for the gamma-decay of the astrophysically important 2.645 MeV state in 20Na. Branching ratios obtained for the first two proton unbound states in 20Na were Gamma_p/Gamma_gamma(2.645 MeV) = 15.1 (+28.8/-8.9) and a lower limit of Gamma_p/Gamma_gamma(2.849 MeV) > 26.0. The experimental branching ratios were compared with theoretical predictions based on shell-model calculations and on the properties of mirror states in 20F. Our results favor a J^pi =1+ assignment for the 2.645 MeV state and a J^pi = 3+ for the 2.849 MeV at the 1-sigma confidence level. Our result also suggests that the resonance strength for radiative capture through the 2.645 MeV state is close to the value of 6 meV, in agreement with the value calculated assuming it to be the mirror of the 3.172 MeV intruder state in 20F with a 6p2h configuration.

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