Main factors affecting the calculation of radiation dose to the lung from inhalation of radon daughters.

The radiation dose to the lung due to inhalation of radon daughter products has been computed with improved data on lung models, aerosol parameters, deposition and clearance mechanisms. The effects of the following factors on the dose calculated for dwellings have been considered in detail: (a) the diffusion coefficient of the unattached daughter products; (b) the activity median diameter (AMD) of the aerosol size distribution; (c) room ventilation rate; (d) air flow rate in the respiratory tracts; (e) lung morphometry; and (f) effect of phase of the tissue-equivalent medium on the stopping power and range for alpha particles. It has been found that realistic changes in values of some factors change the dose rate by a factor of 2. By adopting likely values, it is calculated that annual dose rates in the fifth bronchial generation are typically 4.3 and 1.8 mGy year-1, at the epithelial surface and 20 microns depth, respectively, for a person exposed to a radon concentration of 23 Bq m-3, the average value for U.K. dwellings.