The γ‐Ray‐Induced Electric Conductivity of Fused Silica as Dependent on Field Strength, Temperature, and Irradiation Time

Abstract

AbstractThe γ‐ray‐induced electric conductivity in fused silica is studied theoretically and experimentally as a function of temperature, electric field strength, sample thickness, and irradiation time. Synthetic glasses containing water show the highest induced conductivity. Caused by an increase of positive centres capturing the excited electrons, the conductivity decreases as t−α with the irradiation time t, where α < 1 is a constant depending on temperature. Within the range from 8 to 300 °K, induced currents are measured with voltages up to 2500 V and dose rates between 10 and 200 mrad/s in synthetic samples, 0.2 to 4 mm thick. The gradual transition from constant conductivity at high temperatures and low field strengths F to an increase of conductivity proportional to F cr F3/2 at low temperatures and high field strengths is explained by the deformation of the Coulomb potential of 2 × 1012 to 5 × 1014 cm−3 singly ionized, electron‐capturing centres under the action of the applied field. The comparison of the theoretical dependence of the electron lifetime on field strength and temperature with the measurements allows to conclude that the mobility is independent of temperature. This implies the elastic scattering of the electrons at about 3 × 1019 cm−3 neutral impurities. Furthermore, the mean free path of the electrons for loss of a phonon at 8 °K is determined to be 106 Å.