Application of positron age-momentum correlation measurement to the study of defects in electron irradiated synthetic silica glass

Abstract

Age-momentum measurements and positron lifetime measurements were carried out in order to investigate vacancy-type defects produced in 3 MeV electron irradiated synthetic silica glasses, in which 1 ppm and 300 ppm of –OH bonds were contained. A high formation probability of positronium (Ps) was found for unirradiated specimens. These Ps atoms were considered to be formed in open-volume defects (∼7×10−2 nm3). The formation probability of Ps was drastically decreased by the electron irradiation, especially for the specimens which contained 1 ppm of –OH bonds, even though the size of the open-volume defects and the momentum distribution of electrons at the open-volume defects are independent on the –OH concentration and on the electron irradiation. Since the values of second lifetime components of positron lifetime spectra were ∼300 ps and very close to the estimated value of the lifetime of the positrons which are considered to be trapped in the mono- or divacancies, the decrease of formation probability of Ps can be attributed to an increase of positron annihilation in vacancy-type defects generated by the electron irradiation. Positrons were suspected to be trapped in such defects.