Nuclide-dependent local and collector surface effects in sampling of radioactive deposition to ground

After the end of atmospheric nuclear weapons tests and after the Chernobyl accident, the deposition characteristics of 137Cs changed from a predominant wet deposition to the present resuspension mechanism characterised by predominant dry deposition. To study the consequences of this change for deposition sampling, monthly deposition data from two collectors located at a distance of 600 m were compared from 1991 to 2000. On the average, the deposition rates differed by roughly a factor of two for 137Cs, whereas for the cosmogenic 7Be a difference was not detectable with statistical significance. Further, a “funnel” collector with a mostly dry surface collected on the long-term average 36% less of 137Cs, but 8% less of 7Be, than a “pot” collector with a continuously water-covered surface. Since for 137Cs deposition and the bulk deposition a similar behaviour was found, a stronger sensitivity of other resuspension-derived radionuclides against local and collector surface variations can generally be expected.