Abstract :
The activity size distributions of natural radionuclides 7Be and 40K were measured outdoor in El-Minia city, Egypt by means of gamma spectroscopy. A low-pressure Berner cascade impactor was used as a sampling device. The activity size distribution of both 7Be and 40K was described by one log-normal distribution, which was represented by the accumulation mode. The activity median aerodynamic diameter (AMAD) of 7Be and 40K was determined to be 530 and 1550 nm with a relative geometric standard deviation (δ, which was defined as the dispersion of the peak) of 2.4 and 2, respectively. The same sampling device (Berner impactor) and a screen diffusion battery were used to measure the activity size distribution, activity concentration and unattached fraction (fP) of 212Pb in indoor air of El-Minia City, Egypt. The mean activity median aerodynamic diameter (AMAD) of the accumulation mode for attached 212Pb was determined to be 250 nm with a mean geometric standard deviation (δ) of 2.6. The mean value of the specific concentration of 212Pb associated with that mode was determined to be 460±20 mBq m−3. The activity median thermodynamic diameter (AMTD) of unattached 212Pb was determined to be 1.25 nm with δ of 1.4. A mean unattached fraction (fp) of 0.13±0.02 was obtained at a mean aerosol particle concentration of 1.8×103 cm−3. The mean activity concentration of unattached 212Pb was found to be 19±3mBq m−3. It was found that the aerosol concentration played an important role in varying the unattached, attached activity concentration and unattached fraction (fP).
