Positron Annihilation in Neutron- and Electron-Irradiated Silica Glass

概要

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Positron lifetime and angular correlation of annihilation radiation (ACAR) have been measured on fused and synthetic silica glass before and after irradiation with fast-neutrons up to 8x10^<18> n/cm^2 below 150℃ or with 3 MeV electrons up to 1x10^<18>e/cm^2 below 50℃. Before irradiation positron lifetime spectra show characteristic long-lifetimes due to ortho-positronium (o-Ps) formation and are well decomposed into 3 components with the time constants τ_i (i=1, 2, 3) and the relative intensities I_i (I_1+I_2+I_3=1). The τ_3 lifetime is about 1.7 ns, being nearly independent of the samples, while τ_2 is strongly dependent on the samples, ranging from 0.7 to 1.2 ns. Narrow peaks on the ACAR curves and the τ_3 lifetime give evidence of Ps formation in structural open-spaces (voids) with radius about 0.3nm. By neutron-irradiation the τ_2 lifetime has reduced to about 0.47 ns irrespective to the samples but its intensity (I_2) has increased with the dose. This component suggests positron trapping without Ps formation at irradiation-induced defects such as peroxy radicals. Annealing behavior of lifetime parameters is also presented and compared with previous ESR work.Positron AnnihilationPositroniumSilica GlassIrradiation EffectsVoidsDefects
東北大学の論文
1994-09-16