Use of computer code for dose distribution studies in a 60Co industrial irradiator

This paper presents a benchmark comparison between calculated and experimental absorbed dose values for a typical product, in a 60Co industrial irradiator, located at ININ, Mexico. The irradiator is a two level, two layer system with overlapping product configuration with activity around 300kCi. Experimental values were obtained from routine dosimetry, using red acrylic pellets. Typical product was Petri dishes packages, apparent density 0.13 g/cm3; the product was chosen because of its uniform size, large quantity and low density. Minimum dose was fixed in 15 kGy. Calculated values were obtained from QAD-CGGP code. This code uses a point kernal technique, build-up factors fitting was done by geometrical progression and combinatorial geometry is used for system description. Main modifications for the code were related with source simulation, using punctual sources instead of pencils and an energy and anisotropic emission spectrums were included. Results were, for maximum dose, calculated value (18.2 kGy) was 8% higher than experimental average value (16.8 kGy); for minimum dose, calculated value (13.8 kGy) was 3% higher than experimental average value (14.3 kGy). (author)