Effect of indoor activity size distribution of (222)Rn progeny in-depth dose estimation.

In this work, the attached and unattached activity size distribution of (222)Rn progeny ((214)Bi and (218)Po) were measured indoor. The fraction of attached progeny was collected using a low-pressure Berner cascade-impactor technique. A constructed wire screen diffusion battery was used for collecting the fraction of unattached progeny. Most of the attached activities for (214)Bi progeny were associated with the aerosol particles of the accumulation mode. The active median aerodynamic diameter (AMAD) of this mode for (214)Bi was determined to be 350nm with a geometric standard division (GSD) of 3. The GSD of unattached size distributions for (218)Po was 1.3 with an active median aerodynamic diameter (AMTD) of 1.3nm. Given that dose estimation is sensitive to environmental conditions, an analytical method was introduced to compute the local energy deposition of (218)Po alpha particles in a target volume of 1μm spheres located at different depths in bronchial epithelium. While the depth-dose distributions for nuclides uniformly distributed within the epithelium were found to be practically constant with depth, they decreased in an almost linear fashion with increasing depth for nuclides on the airway surface.