Direct total body Bi measurements and their implications for radon dose assessment.

Direct Bi bioassays may elucidate some of the uncertainties related to the relationship between the ambient concentration of radon and its short-lived decay products and the corresponding radiation burdens of individual human subjects. Sequential total body Bi activity measurements were carried out on a group of 67 healthy adult volunteers living in a region with moderate airborne radioactivity and conducting similar daily activities using a whole-body counter equipped with sixteen NaI(Tl) detectors. The total body Bi activity in the studied subjects was related to gender, fat-free mass and the season of the year. Approximately 95% and 92% of the Bi activity measured during the cold seasons of the year in men and women, respectively, was attributed to radon progeny inhalation. Following acute exposure to high airborne radioactivity over a short time period, the Bi enhancement in a volunteer decreased exponentially with time post-exposure, with a half-time of about 40 min. Taking into account the anticipated low Bi activity in the vast majority of individuals, and the uncertainties in Bi biodistribution even during counting, accurate measurements can be obtained using high-sensitivity whole-body counters with almost geometrical invariant counting efficiency.