Activity size distributions of some naturally occurring radionuclides 7Be, 40K and 212Pb in indoor and outdoor environments

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 ( f P) 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 ( f p) of 0.13±0.02 was obtained at a mean aerosol particle concentration of 1.8×10 3 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 ( f P).