Monte Carlo simulation of a scanning detector whole body counter and the effect of BOMAB phantom size on the calibration

Monte Carlo simulation has been used to model the Human Monitoring Laboratory's scanning detector whole body counter. This paper has also shown that a scanning detector counting system can be satisfactorily simulated by putting the detector in different places relative to the phantom and averaging the results. This technique was verified by experimental work that obtained an agreement of 96% between scanning and averaging. The BOMAB phantom family in use at the Human Monitoring Laboratory was also modeled so that both counting efficiency and size correction factors could be estimated. It was found that the size correction factors lie in the region of 2.4 to 0.66 depending on phantom size and photon energy. The efficiency results from the MCNP scanning simulations were 97% of the measured scanning efficiency. A single function that fits counting efficiency, size, and photon energy was also developed. The function gives predicted efficiencies that are in the range of +10% to -8% of the true value.