Lung dosimetry based on the inhalation of 212Bi

In the case of internally deposited radionuclides, direct measurement of the energy absorbed from ionizing radiation emitted by the decaying of these radionuclides is rarely, if ever, possible. Therefore, one must rely on dosimetric models to obtain estimates of the spatial and temporal patterns of energy deposition in human lung. These models always require information about the parameters of activity size distributions of thoron and radon progeny. In the present work, the attached and unattached activity size distribution of 212Bi was measured in outdoor air of El-Minia, Egypt. The attached fraction was collected using a low pressure Berner cascade impactor technique. A constructed screen diffusion battery was used for collecting the unattached fraction. Most of the attached activities for 220Rn (212Bi) progeny were associated with the aerosol particles of the accumulation mode. An analytical method has been developed to compute the local energy deposition of 212Bi alpha particles in a target volume of 1μm spheres located at different depths in bronchial epithelium. In order to reach the target, alpha particles travel either through tissue alone or through air and tissue. While the depth-dose distributions for nuclides uniformly distributed within the epithelium were practically constant with depth, they decreased in an almost linear fashion with increasing depth for nuclides on the airway surface