Shielding calculations for changing from circular to a rectangular source configuration for a pilot scale irradiator

The Radiation Technology Centre (RTC) of the Ghana Atomic Energy Commission operates a 1.85 PBq Co-60 gamma irradiator for research, food preservation and medical sterilization. It has become necessary to improve the dose rate delivered by changing the circular arrangement of sources to a rectangular one. The irradiator needs upgrading from 1.85 PBq to 18.5 PBq for cost effective operations. Since funding is not readily available, changing the geometry of the source is an option being considered. The elliptical and line source approximations methods for calculating the dose rate for the proposed rectangular Co-60 source are described and used to ascertain whether additional shielding will be required or not. The initial dose rate at 1.0 m from the cylindrical source was 368 Svh-1 but the elliptical source method gave 625 Svh-1 whilst the line source method predicted 649 Svh-1, if the source was considered rectangular. From these calculations, the dose rates at the occupied sites ≥ 5.0 m, require concrete wall shielding of thickness, t = 183.1 cm as against the 190 cm which is now in place at the RTC. This implies that the biological shield in place is adequate for the replacement of the cylindrical source cage with a rectangular or plaque type. (au)