Long-term variation ž1986 1998/ of post-Chernobyl 90Sr, 137Cs, 238Pu and 239,240Pu concentrations in air, depositions to ground, resuspension factors and resuspension rates in south Germany

Annual mean concentrations in air and annual total Žwet plus dry. depositions to ground of 90Sr, 137Cs, 238Pu and 239,240Pu decreased at Neuherberg, south Germany, in the period from July 1986 Ži.e. after the end of the initial deposition phase from Chernobyl. to 1998 as follows: 90Sr from 0.77 to 0.05 Bq m 3, and from 0.82 Ž1988. to 0.28 Bq m 2 year 1; 137Cs from 133 to 2.8 Bq m 3, and from 116 to 3.8 Bq m 2 year 1; 238Pu from 0.95 to 0.063 nBq m 3, and from 1.0 to 0.23 mBq m 2 year 1; 239,240Pu from 8.1 to 0.53 nBq m 3, and from 6.4 to 2.1 mBq m 2 year 1.The values for the non-caesium radionuclides are compared to the few available data from other stations. After an initial phase which is characterised for a given radionuclide by the varying ratio of the Chernobyl-derived inventory to the earlier, weapons fallout-derived inventory, the time courses of concentrations of 137Cs, 90Sr, 238Pu and 239,240Pu in air become more or less parallel Žfrom about 1990., despite the considerable differences in the physico-chemical properties of these elements. By contrast, the time series of radionuclide deposition rates show until about 1994 less similarity among each other and with the respective concentration series in air. From 1994, concentrations in air and depositions to ground become nearly constant, or decrease very slowly. At the end of the observation period, resuspension factors between 1.4 10 10 m 1 and 1.0 10 11 m 1 are observed for the various nuclides. The time courses of specific activities ŽBq g 1. as well as the time courses of radionuclide ratios show characteristic differences between air and deposition. The data will be useful in predicting the post-accident behaviour of radionuclides a long time after a large-scale contamination event.