Abstract: The present invention relates to a product irradiator having a cartridge loading system. The cartridge comprises a plurality of carriers or totes which are transported as a single mass into an irradiation chamber for radiation processing. Products contained within the totes are irradiated while on the cartridge, but individual totes are transferred around the radioactive source by a tote transfer system. The cartridge product irradiator permits quick changes of cartridges thereby minimizing the time that the radioactive source is not in use, and also permits good radiation dose uniformity in products. The cartridge product irradiator is thus highly efficient and economical to use.