Dosimetry studies for an optimized reloading of a panoramic Cobalt-60 source using FLUKA Monte Carlo code

The Cobalt-60 source used at the Tunisian Gamma Irradiation Facility is nearing the end of its useful life. Due to the current low dose rates, the irradiation process takes a long time. To address exposure time and cost issues, source racks need to be reloaded to improve the quality of the exposure process. This work aims to find the optimal new configuration for future reloading of the Cobalt-60 source rack and to evaluate the dose rate distribution in the vicinity of the Irradiator and the Dose Uniformity Ratio (DUR) in a dummy product. When keeping old pencils, the optimal configuration will need to be adjusted to accommodate the new Cobalt-60 pencils. The replenishment method developed using FLUKA-based Monte Carlo code involved the addition of six new pencils: three in the upper top (outer) holder of the source rack and three in the lower bottom (inner) source holder. The spatial distribution of dose rates in the vicinity of the source rack before and after reloading was evaluated. For the radiation processing, the maximum and minimum absorbed dose in the dummy product were estimated to calculate the DUR value. The DUR value for a single-use medical product is about 2.5. The results obtained before and after reloading show that the spatial distribution of the dose rate is uniform for the proposed configurations, and has a value of approximately 0.4 kGy/h after reloading at the conveyor belt location.