ATTACHED AND UNATTACHED ACTIVITY SIZE DISTRIBUTION OF SHORT-LIVED RADON PROGENY (214Pb) AND EVALUATION OF DEPOSITION FRACTION

Inhalation of 222Rn progeny in 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 radon progeny. The current study presents measured data on the attached and unattached activity size distributions of radon progeny in indoor 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 222 Rn progeny were associated with aerosol particles of the accumulation mode. The mean activity median aerodynamic diameter (AMAD) of this mode for 214Pb was determined to be 401 nm with relative mean geometric standard deviation of 2.96. The mean value of specific air activity concentration of 214Pb associated with that mode was determined to be 4.74 ±0.44 Bq m-3. The relative mean geometric standard deviations of unattached 214Pb were determined to be 1.21 with the mean activity thermodynamic diameter (AMTD) of 1.2 nm. The mean unattached activity concentration of 214Pb was found to be 0.44 ±0.14 Bq m-3. Based on the obtained results of radon progeny size distributions (unattached and attached), the deposition fractions in each airway generation of the human lung were evaluated by using a lung deposition model.