MCNPX Modelling of G-M Pancake Response to Radioiodine Charcoal Filter Used at OPG

Abstract

The Monte Carlo N-Particle eXtended (MCNPX) radiation transport code was used to model the response of a G-M pancake detector to the charcoal-filled radioiodine cartridge air filter used at Ontario Power Generation (OPG). The MCNPX models used either a continuous beta spectrum, or the discrete photon energies from 131I, exclusively. The electron and photon results were combined to determine the overall response of the G-M pancake probe. The model of the probe was benchmarked against 60Co and 36Cl certified button sources. The model of the charcoal filter was adjusted and benchmarked against a certified 131I cartridge source. The results were in a very good agreement with the experimental data.