Evalution of minimum detection activity in a portable whole body counter using monte carlo method

A portable body counter detects internal contamination in an emergency. Monte Carlo code estimates minimum detection activity (MDA) for a portable whole-body counter. In the case of outdoor open fields, natural background radiations were simulated. This counter has a chair geometry equipped with a NaI (Tl) detector (5cm x 5cm) inside a lead shield collimator consisting of a set of lines and a continuous component with monenergistic γ sources ranging from 300 to 2000 keV at intervals of 100 keV. This data matrix is folded with the measured spectrum outside the setup to estimate the observed spectrum in the detector. We evaluated the variation of the detector flux transmitted through the lead collimator and chair shield. This was done at different lead densities and different photon energies. Computational data were used to estimate the monitoring system MDA. This method is cheaper to design and test a counter system for low-level counting of γ emitting radionuclides than experimental methods.