The ^(16)O(α,γ)^(20)Ne and ^(28)Si(α,γ)^(32)S reactions at low energy

Citation

Toevs, James Waldo (1970) The ^(16)O(α,γ)^(20)Ne and ^(28)Si(α,γ)^(32)S reactions at low energy. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05172010-110558216

Abstract

The ^(28)Si(α,γ)^(32)S and ^(16)0(α,γ)^(20)Ne reactions have been investigated to provide data for the calculation of the stellar rates of these reactions. The gamma rays were counted with a NaI(Tl) detection system having a high detection efficiency which is approximately independent of the gamma-ray cascade structure of a nuclear level; the detection efficiency was determined experimentally. The reaction ^(28)Si(α,γ)^(32)S was studied for He^+ bombarding energies from 1.4 to 2.7 MeV, and in this region, five new resonances were found, and their strengths, (2J+1) Γ_α Γ_γ/ Γ were measured. An upper limit for the cross section has also been established for bombarding energies below 1.7 MeV. The ^(16)0(α,γ)^(20)Ne reaction was investigated in the energy region from 0.85 to 1.8 MeV; strengths for the previously known resonances were measured, and an upper limit for the cross section was determined for energies below 1 MeV. Stellar interaction rates and photodisintegration rates have been calculated from the measured resonance strengths, and semi-empirical fits to these rates have been given to facilitate astrophysical calculations.

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