Abstract
A whole body counter (WBC) is used in nuclear power plants (NPPs) to identify and measure internal radioactivity of workers who is likely to ingest or inhale radionuclides. A WBC has several counting geometries, i.e. the thyroid, lung, whole body and gastrointestinal tract, considered with the location where radionuclides are deposited in the body. However, only whole body geometry is normally used to detect internal radioactivity during whole body counting at NPPs. It is overestimated internal exposure dose because this measured values are indicated as the most conservative radioactivity values among the them of other's geometry. It is often possible to estimate external contamination as internal contamination due to radionuclides attached to the skin of radiation workers and this leads to an excessively conservative estimation of radioactive contamination. In this paper, the reanalysis of previous experiments for radioactivity depending on the counting geometry of WBC using phantoms and standard radiation sources was carried out in order to improve overestimated internal exposure dose. Quantitative criteria could be used for selecting the optimal WBC counting geometry. Furthermore, discrimination guideline according to ratio of count rates of the upper and lower detectors of the WBC is provided through statistical analysis method.