Lifetimes and branching ratios of energy levels of 28Si. II

Abstract

The gamma rays from the 25Mg(α,nγ)28Si reaction have been studied for alpha-particle energies in the range 6.0 MeV to 7.2 MeV. A 25-cm3 Ge(Li) gamma-ray counter was used to observe the complex high energy gamma-ray spectra at angles between 0° and 130° to the alpha-particle beam. The lifetime ofthe7798-keV level was found to be 0.30 ± 0.10 ps by studying the Doppler broadening of the spectrum lines. The gamma-ray decays of the 8260, 8328, 8411, 8543, and 8587-keV levels were observed. The gamma-ray decays of the 8260 and 8543-keV levels had not been observed previously. The 8260-keV level decays to the first excited level at 1780-keV and the 8543-keV level decays only to the 4617-keV level. Information on the spin-parity combinations of these levels in 28Si was obtained by a measurement of the yield of alpha particles at zero degrees to the beam in the reaction 16O(16O,α)28Si.