Internal calibration for a total body counter.

Whole body counting is used to monitor the ingestion of radioactivity by radiation workers when unsealed sources are used in biomedical or industrial applications. The whole body counter at Lucas Heights Research Laboratories has been running for four decades, and radiation workers are frequently monitored for radioactive contamination. In a retrospective study of total body potassium (TBK) values in radiation workers, it was found that the results varied markedly with time. In that TBK is a slowly varying quantity in healthy individuals, variation in TBK is therefore indicative of instability in the counting system. We conclude that TBK can be used as an internal calibration for the whole body counter. The activity of radioisotope contaminants can therefore be expressed relative to the value of the potassium activity in a given subject.