Variable-energy positron-beam studies of SiO2/Si irradiated by ionizing radiation

Variable-energy positron-beam studies have been carried out on Si with a 1.61 μm overlayer of SiO2 irradiated by x ray and γ ray up to the dose of 5×105 R. The Doppler broadening of annihilation photons was found to be strongly influenced by x-ray irradiation, and the effect was extended homogeneously over the entire oxide layer. A trapping model which neglects positron diffusion effects was applied to the dependence of the line shape parameter S on incident positron energy.