Radiation Protection Dosimetry 7:147-150 (1984)
© 1984 Oxford University Press
Radon Daughter Activity Size Distributions
The size distributions of radon and thoron daughters have been measured in buildings and in the open air. Because of the low radioactivity concentration a high volume cascade impactor was used. The cascade impactor data were evaluated by means of an improved computer programme taking into account the effect of interstage losses on the measured precipitation values of the impactor. The size distributions found for the shortlived radon daughters, 214Pb, 214Bi, and thoron daughter, 212Pb, were unimodal log-normal. There was no significant difference between activity size distributions of the short lived radon decay products and the thoron daughter 212Pb. The activity median aerodynamic diameter (AMAD) measured in different buildings and at different days ranged from 0.07 µm to 0.29 µm with a mean value of 0.18 µm for the radon and thoron daughters in dwellings with low room ventilation. The mean value of the geometric standard deviation was sg = 3.50. The size distributions in the open air are shifted significantly to larger particle sizes with a mean AMAD of 0.39 µm (range: 0.20 to 0.54 µm) and a mean standard deviation of sg = 2.31.