Activity of Ultrafine Fraction of Radon Progeny in Indoor Air

Inhalation of Rn progeny has been recognized as a health risk, primarily as a cause of human lung cancer. Rn progeny in the domestic environment contributes the greatest fraction of the natural radiation exposure to the public. The ultrafine activity of these progeny amounts up to about 10 percent of the total activity (attached and ultrafine), but is considered to yield about 50 percent of the total radiation dose. Therefore, measurements of ultrafine fraction are essential for the estimation of radiation dose. The current study presents measured data on the total equilibrium equivalent concentration (EEC) and ultrafine equilibrium equivalent concentration ( EEC), ultrafine fraction (fb), and unattached activity size distributions of radon progeny in the low ventilated room at Minia University, Minia City, Egypt. A screen diffusion battery was used for collection the ultrafine fraction and measuring the total activity concentration of radon progeny. The EEC of radon progeny was varied between 1.3 and 18.9 Bq m with a mean value of 5.2 ± 0.48 Bq m. The mean activity thermodynamic diameter (AMTD) of ultrafine of radon progeny was determined to be 1.26 nm with relative mean geometric standard deviations (GSD) of 1.3. The ultrafine fraction of radon progeny, fb, has a range 0.01 to 0.21 with an average of 0.08 ± 0.03. Based on the above experimental results, the deposition fractions have been evaluated in each air way generation through the human lung by applying a lung deposition model. The effect of radon progeny deposition by adult male has been also studied for various levels of physical exertion. The dose conversion factor has been discussed as a function of fb. Finally, the annual dose was calculated to be 0.36 mSv.