A general phantom procedure for calibrating inhaled 212Pb body burdens

A whole-body counting procedure for phantom calibration of inhaled 212Pb body burdens is developed. The 2.62 MeV photons from the associated 208Tl serve as an indicator of internal 212Pb contamination, and the spectra of uncontaminated volunteers are used to ascertain the existence and scale the magnitude of body burdens possessed by individuals of different effective thickness. Based on metabolic considerations, a quasi-uniform 212Pb-212Bi corporal distribution is assumed to be eastablished 15 to 24 hr after inhalation, and a calibration phantom is accordingly constructed, details of which are given. The calibration relation constructed by comparing the individual's measured 208Tl counting rate with that of a compatible theoretical phantom of known 228Th activity was applied to whole-body counting of workers from a Brazilian gas mantle (ThO2) factory, and shown to provide reasonable agreement with measured airborne 212Pb activity there. Finally, sources of error in the calibration scheme are discussed, and suggestions for future improvements are presented. (author)