Electrical Conductivity Induced in Insulators by Pulsed Radiation

The minimum prompt photoconductivity induced by pulses of x rays, gamma rays, and energetic electrons in various amorphous and disordered insulating organic and inorganic materials is predicted on the basis of data for the scattering of hot electrons in solids and the band gap for insulators. For total doses of 3 × 104 to 30 × 104 rad or greater, the minimum prompt photoconductivity is predicted to be linear with dose rate, γ, and is given by σ(γ-1cm-1)=5×10-19ρ0γ/Eg2, where ρ0 is the density (g/cm3) and Eg is the optical band gap (eV). This formula agrees well with data for a variety of plastics, mica, and borosilicate glass under widely different irradiation conditions. The formula considerably underestimates absolute values of prompt conductivities observed for Al2O3, MgO, and certain plastics, because the model does not hold for ordered materials.