Total Yield Measurements for the ²⁴Mg(α,γ)²⁸Si and ²⁷Al(ρ,γ)²⁸Si Reactions

Citation

Lyons, Peter Bruce (1969) Total Yield Measurements for the ²⁴Mg(α,γ)²⁸Si and ²⁷Al(ρ,γ)²⁸Si Reactions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7ESS-6977. https://resolver.caltech.edu/CaltechTHESIS:06252018-100112879

Abstract

The ²⁷ Al (ρ,γ)²⁸Si and ²⁴Mg(α,γ)²⁸ Si reactions have been investigated to provide the data needed for calculation of the ²⁸Si photodisintegration rate in astrophysical situations, particularly in the silicon-burning stage of stellar nucleosynthesis. A large solid angle NaI gamma ray spectrometer was employed which provided high detection efficiencies. The ²⁷Al(ρ,γ)²⁸Si reaction was investigated over the proton energy range O.3 – 2.6 MeV; total gamma ray strengths were determined for 85 resonances. From 1.4 – 2.6 MeV, the gamma ray yield curve was measured and an upper limit for the nonresonant cross section was determined. Where possible, total resonance widths were deduced from the data. The gamma-ray detection efficiencies and target purity were investigated experimentally. Comparison was made with resonance strengths, measured by other methods, in the reactions ³⁰Si(ρ,γ) ³¹P and ²⁶Mg(ρ,γ)²⁷Al. The reaction ²⁴Mg(α,γ)²⁸Si was investigated for alpha particle energies up to 2.8 MeV; total gamma ray strengths were determined for 16 resonances, including a previously unreported resonance at 1.358 ± O.007 MeV. Stellar interaction and photodisintegration rates were calculated from the measured resonance strengths, and semi-empirical fits to these rates were determined for use in astrophysical calculations.

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