AIR KERMA DISTRIBUTION IN AN IRRADIATION FACILITY - COMPARISON OF MONTE CARLO SIMULATIONS WITH PHYSICAL DOSIMETRY

摘要

In order to evaluate the effectiveness of Monte Carlo methods applied to shielding calculations, an air kerma rate evaluation was performed in different locations of a ~(60)Co gamma irradiator, operated for industrial and research purposes in a state laboratory at Nuclear and Technological Institute near Lisbon. The MCNPX code was used to perform the radiation transport simulation along the facility. Variance reduction techniques were used by implementing, among others, the weight window generator to account for the air kerma rate in the access maze leading to the facility's irradiation chamber. Analog Monte Carlo simulations were also performed to test the correct implementation of the nonanalog techniques used and to evaluate the computational efficiency gain. The validation of the computational results is discussed by comparison with physical dosimetry measurements using ionization chambers. The results obtained show a good agreement between the simulations and the measurements for the positions in and the exit of the irradiation room. Discrepancies were found for the positions where the air kerma rate is lower resulting from the deeper penetration of radiation across the shields and scattering through the maze walls. Further insight must be gained to improve the results at these positions.