Direct total body ²¹⁴Bi measurements and their implications for radon dose assessment

Direct ²¹⁴Bi 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 ²¹⁴Bi 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 ²¹⁴Bi activity in the studied subjects was related to gender, fat-free mass and the season of the year. Approximately 95% and 92% of the ²¹⁴Bi 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 ²¹⁴Bi enhancement in a volunteer decreased exponentially with time post-exposure, with a half-time of about 40 min. Taking into account the anticipated low ²¹⁴Bi activity in the vast majority of individuals, and the uncertainties in ²¹⁴Bi biodistribution even during counting, accurate measurements can be obtained using high-sensitivity whole-body counters with almost geometrical invariant counting efficiency.