Comparison of outdoor activity size distributions of 220Rn and 222Rn progeny.

Inhalation of 222Rn and 220Rn progeny from the domestic environment contributes the greatest fraction of the natural radiation exposure to the public. Dosimetric models are most often used in the assessment of human lung doses due to inhaled radioactivity because of the difficulty in making direct measurements. These models require information about the parameters of activity size distributions of thoron and radon progeny. The present study presents measured data on the attached and unattached activity size distributions of thoron and radon progeny in outdoor air in El-Minia, Egypt. The attached fraction was collected using a low-pressure Berner cascade impactor technique. A screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for 222Rn and 220Rn progeny were associated with aerosol particles of the accumulation mode. The activity size distribution of thoron progeny was found to be shifted to slightly smaller particle size compared to radon progeny.