Deposition and clearance for radon progeny in the human respiratory tract

In vivo counting of Pb-214 was conducted to estimate the deposition and retention of radon progeny in the human respiratory tract. Two volunteer subjects were exposed to high radon concentrations. After the exposures, activity deposited in the extrathoracic (ET) region for each subject was measured using a NaI(Tl) detector. According to the International Commission on Radiological Protection (ICRP) model, a reference value for particle transport rate from ET2 to the GI tract is 100 d(-1) (half-time, 10 min). The effective half-time of Pb-214 deposited in the ET region was calculated for pure nose and mouth breathers, using the ICRP reference transport rate. While the measured half-times for nose breathers were generally consistent with the calculated values, those for mouth breathers were significantly larger than the calculated values. The results indicated that the particle transport rate from ET2 to the GI tract was much smaller than the reference value in the ICRP model.