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

Abstract

The gamma rays from the 25Mg(α,nγ)28Si reaction have been studied using alpha particles with energies ranging from 4.8 to 6.0 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. Estimates of the nuclear lifetimes of the energy levels excited were obtained from Doppler shift attenuation measurements. The de-excitation branching ratios of the levels were also measured. The existence of a new level in 28Si at 6695 keV was confirmed. The recently reported 3− level at either 6880 keV or 6889 keV was observed and found to be the 6880-keV member of the doublet. The enhancement of the octupole transition to the ground level of 28Si was found to be 13 Weisskopf units.