Photoreactions in 28Si Nucleus by Monochromatic Gamma-Rays

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Abstract
The structure of the giant resonance in 28 Si has been studied using monochromatic gamma-rays ( Δ E γ / E γ ≈1%) from proton capture reactions. A silicon solid-state detector served both as target and detector. Total cross sections for the 28 Si (γ, p 0 ), (γ, p 1 ), (γ, p 2 ), (γ, α 0 ) and (γ, α 1 ) reactions were obtained from 17.4 to 22.3 MeV and the integrated cross sections were 34.4, 18.9, 17.6, 1.6 and 2.7 mb·MeV, respectively. The excitation functions of proton emission showed many discernible fine structures. Most of the peaks of the cross sections for different exit channels occurred at the same gamma-ray energy and the number of resonance states involved in a peak seems to be a few. The (γ, α 0 )-reaction excitation functions revealed several humps which are possibly caused by an E 1 absorption. Isotopic-spin selection rule seems no longer to be valid for the present (γ, α 0 ) reaction. Comparisons were made with the calculated absorption probability from the Nilsson model.