X-Ray Induced Electrical Polarization in Glass

Electrical polarization in a lead silicate glass induced by the action of x-rays on the material is found to exist. This phenomenon is surveyed experimentally as a function of total dose (incident and absorbed), dose rate, x-ray tube potential, radiation temperature, and temperature at which the polarization is released and measured. Net surface charges of the order of 10^-9 coulomb/cm² can be obtained from 3-mm thick samples irradiated at room temperature with 10⁵ r of 250-kv x-rays. To the first order the build-up and decay of this condition seems to follow the normal electrical relaxation as can be theoretically predicted from the dielectric and resistivity constants of the material (τ=ρε). Measured surface charge is shown to be proportional to absorbed dose for smaller doses; however, for greater doses final equilibrium in the polarization is reached when back electrical conduction becomes as large as the forward x-ray induced displacement current. The dependence of measured surface charge upon the sample thickness has been experimentally investigated for one case.