Investigation of backward α-particle scattering in 24Mg and 28Si through α-γ angular correlations

Alpha-gamma angular correlations have been measured for the reaction 24Mg(α,α'γ) in the energy range 15.50 to 17.00 MeV in steps of 300 keV and for 28Si(α,α'γ) from 15.00 to 16.20 MeV in steps of 200 keV to provide energy averaged results. The scattered α-particles were detected for lab angles thetasub(α) = 1150-1780 in a multidetector arrangement. The coincident γ-rays were observed with a Ge(Li) detector placed at 900 in the reaction plane. Data were obtained for the 1st, 2nd and 3rd excited states of 24Mg and for the 1st, 2nd, 3rd and 4th excited states of 28Si. The absolute double-differential cross sections were analysed with Hauser-Feshbach calculations. The analyses show that compound nuclear processes are responsible for the rise of backward α-scattering in 24Mg(α,α'γ)24Mg and 28Si(α,α'γ)28Si at the energy studied. (Auth.)