Air activity concentrations and particle size distributions of the Chernobyl aerosol

The concentrations of radioactive isotopes attached to aerosol particles resulting from the accident in the nuclear power plant at Chernobyl were determined in the ambient air of Goettingen (FRG) during May 1986 by means of gamma spectroscopy. Measurements of the activity concentration of the long lived fission product 137Cs were continued up to December 1986. During May some measurements were performed with charcoal filters to determine the gaseous fraction of 131I. Size distributions of the radioactive aerosol particles were determined by a low pressure Berner impactor and a high volume Sierra impactor. Most of the measurements yield unimodal distributions with activity median aerodynamic diameters (AMAD) in the range 500-1000 nm. Some distributions were bimodal with an additional AMAD in the size range greater than 5000 nm. The AMADs of the 131I distributions were shifted to slightly smaller values than those of the other isotopes. In some air samples 'hot particles', containing the isotopes 95Zr, 95Nb, 141Ce and 144Ce were determined with diameters in the size range 2000-5000 nm and activities of about 0.3-3.1 Bq. (author)