Dose Enhancement Effects in a Shepherd Model 81-22 Cobalt-60 Irradiator

The magnitude of the low energy component of the photon energy spectrum inside a J. L. Shepherd Model 81-22 Co-60 irradiator has been experimentally determined. Thermoluminescent dosimeters and a specialized ionization chamber were used to verify the usefulness of a lead (0.06") and aluminum (0.03") filter box to harden the Co-60 photon energy spectrum. The area of uniform dose as a function of distance from the Co-60 source inside the irradiator also has been determined. The results suggest two recommendations for use of the irradiator: the Pb/Al box should be used for all irradiated samples where low energy radiation can be a factor, and samples should be placed as close to the source as possible, while maintaining a uniform dose rate over the entire sample area.