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

In this work, the attached and unattached activity size distribution of 222Rn progeny (214Bi and 218Po) 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 214Bi progeny were associated with the aerosol particles of the accumulation mode. The active median aerodynamic diameter (AMAD) of this mode for 214Bi was determined to be 350 nm with a geometric standard division (GSD) of 3. The GSD of unattached size distributions for 218Po was 1.3 with an active median aerodynamic diameter (AMTD) of 1.3 nm. Given that dose estimation is sensitive to environmental conditions, an analytical method was introduced to compute the local energy deposition of 218Po alpha particles in a target volume of 1 μm 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.