Thermally generated electrical currents in γ-irradiated Lucite

Thin disks of commercial polymethylmethacrylate (Lucite), after having been exposed to γ-rays, exhibit electrical currents, in the absence of an externally applied electric field when the samples are heated under the proper conditions. The currents are generated only if (a) the sample is heated with the maintenance of a temperature difference between the electrodes or (b) it is heated without a net temperature difference between the electrodes and the γ-irradiation was directional with a net component normal to the electrode surfaces and with relatively high-energy photons. For case (a), the direction of charge movement corresponds to positive charge displacement toward the colder electrode. For case (b), the direction of charge movement corresponds to positive charge displacement toward the exit side of the sample.