The ¹⁶O(α,γ)²⁰Ne and ²⁸Si(α,γ)³²S Reactions at Low Energy

Author: Toevs, James Waldo

Year: 1970

Degree: Dissertation (Ph.D.)

Advisors: Fowler, William A.; Barnes, Charles A.

Committee Member: Unknown, Unknown

Option: Physics

DOI: 10.7907/MHA9-5P97

Abstract

The ²⁸Si(α,γ)³²S and ¹⁶O(α,γ)²⁰Ne 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 ²⁸Si(α,γ)³²S 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 ¹⁶O(α,γ)²⁰Ne 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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