Gamma photoconductivity of Al2O3

Abstract

The electrical conductivity of single-crystal and sintered Al2O3 which occurs during bombardment with y rays has been measured in radiation fields up to 106 R/h, using a 60CO source. The conductivity was different for different crystals and the largest value observed was 0.7 × 10−16 (Ω-cm-R/h)−1; the value for ruby (Al2O3 + 0.05 % Cr2O3) was 100 times smaller. The filling of traps by electrons (or holes) manifested itself during the initial radiation of a specimen as a reduced conductivity until the traps were filled: the density and cross section of these traps were ~1017 per cm3 and ~10−17 cm2, respectively. The shape of the conductivity vs. time curve during the initial radiation is explained by a model which takes into account the excitation of electrons from traps into the conduction band by the energetic electrons resulting from the gamma radiation. It is shown that this model is able to account quantitatively for the observations, if it is assumed that the time required for a secondary electron to lose energy from 10 to 2 eV is somewhat longer than the time associated with the ionization of a filled trap. Conductivity glow curves were observed in all specimens using internal polarization of the specimens and at least four distinct traps were observed with energies in the range 1–2 eV; these are thought to arise from crystal structure defects.