Evaluation using Geant4 of the transit dose in the Tunisian gamma irradiator for insect sterilization

A simulation study of the Tunisian Gamma Irradiation Facility for sterile insects release programs has been realized using the Geant4 Monte Carlo code of CERN. The dose was calculated and measured for high and low dose values inside the irradiation cell. The calculated high dose was in good agreement with measurements. However, a discrepancy between calculated and measured values occurs at dose levels commonly used for sterilization of insects. We argue that this discrepancy is due to the transit dose absorbed during displacement of targets from their initial position towards their irradiation position and displacement of radiation source pencils from storage towards their irradiation position. The discrepancy is corrected by taking into account the transit dose.