Activity size distribution of the short-lived and long-lived radionuclides in outdoor air

There are a number of radioactive isotopes of different elements in the atmosphere near ground level. Most of them are decay products from the 238U- and 232Th-chains with the highest activity concentration of the short-lived 222Rn-(radon)(1-100 Bq/m3) and 220Rn-(thoron) (0.01-1 Bq/m3) decay products. The long-lived radon decay products (210Pb/210Po) have concentrations between 1-5x10-4 Bq/m3. In contrast to these nuclides the amount of the activity concentration of 7Be (1-7x10-3 Bq/m3)is produced by interaction of the cosmic rays with atmospheric gases. Most of these airborne radionuclides are adsorbed on the surface of aerosol particles and form radioactive aerosol. Therefore the behaviour of the airborne radionuclides is determined by the behaviour of the aerosol particles in the atmosphere. Besides the generation rate the activity concentration of the radionuclides in air is influenced by their transport in the atmosphere and by the radioactive decay. In addition, for the longer-lived radionuclides (half-live >1 d) the removal processes (dry deposition, wet deposition) from the atmosphere have an influence on the activity concentration and the coagulation process will significantly change the activity size distribution of the original radioactive aerosol. The activity size distribution of the radioactive aerosol is the dominant parameter for the behaviour of the radionuclides in the environment. The removal processes from the atmosphere, the deposition rate on ground and vegetation and the deposition probability in the lung during inhalation depend on the particle size. In this paper the measurement results of the activity size distribution of the short-lived (218Po, 214Po) and the long-lived (210Pb, 210Po) radon and thoron (212Pb, 212Po) decay products and 7Be are summarised, obtained from measurements over a longer period in outdoor air during the last years. Especially, the aim was to find out the differences between the size distributions of these radionuclides. Therefore it was important to use measurement techniques, which made it possible, to register simultaneously almost all of these radionuclides during one measurement run over a longer time period