Responses of a whole-body counter to distribution of ingested Cs-137 within the body were evaluated using Monte Carlo simulation. The uncertainties in evaluation of Cs-137 body burdens due to counting efficiencies of the whole-body counter were estimated. It was found from calculation that counting efficiencies of the whole-body counter are largely dependent on the 137Cs distribution within the body, and Cs-137 body burdens would be underestimated by a factor of 3 in the worst case.
To testify a calibration method for the whole-body counter using Monte Carlo simulation, counting efficiencies for simple-geometric-form models and phantoms were obtained by simulation and actual measurements. The calculations by Monte Carlo simulation are in good agreement with the measurements.