Effect of dry deposition, washout and resuspension on radionuclide ratios after the Chernobyl accident.
The temporal variations of radionuclide ratios in air and deposition samples collected simultaneously at Munich-Neuherberg (F.R.G.) after the Chernobyl accident have been studied. Until 8 May 1986, the radionuclides investigated were 99Mo, 103Ru, 106Ru, 110mAg, 125Sb, 129mTe, 132Te, 131I, 134Cs, 137Cs, 140Ba, 141Ce and 144Ce. After 8 May, 99Mo, 110mAg, 125Sb, and the Ce isotopes were below the detection limits. Considerable temporal variations of the above radionuclides, relative to 137Cs, were observed in air as well as in deposition. In air the temporal variations reflect the arrival of different parts of the reactor plume with different elemental composition. In deposition, the temporal patterns were quite different from those in air for a given radionuclide. This is explained by varying contributions of dry and wet deposition. Until 8 May, the washout ratios of the above radionuclides covered a range from 240 to 5600, with smaller variations for all radionuclides within one event (e.g. 460-910), and larger variations from one event to another (e.g. 460-3300 for 137Cs). The dry deposition velocity of 137Cs was found to be 0.27 cm s-1, similar to that of 110mAg, aerosol 131I and 140Ba (0.37, 0.13 and 0.15 cm s-1). Another group of radionuclides includes 103Ru, 106Ru, 125Sb, total 131I and 132Te with dry deposition velocities of 0.08, 0.10, 0.07, 0.03 and 0.08 cm s-1 and with temporal variations in deposition which are quite different from those of the first group. From 8 May to the end of June, the washout ratios increased to values between 1500 and 24,000, with the exception of iodine, which had considerably lower washout ratios of between 37 and 4400. These later effects are explained by resuspension and, in the case of iodine, by remobilization of gaseous species.
Rosner
G
G
GSF-Institut für Strahlenschutz, Neuherberg, Federal Republic of Germany.
Hötzl
H
H
Winkler
R
R
D000059:Accidents; D000396:Air Pollutants, Radioactive / Q000032:analysis; D005860:Germany, West; D009688:Nuclear Reactors; D011847:Radioactive Fallout / Q000032:analysis*; D011848:Radioactive Pollutants / Q000032:analysis*; D011891:Rain; D014455:Ukraine
D000396:Air Pollutants, Radioactive; D011847:Radioactive Fallout; D011848:Radioactive Pollutants