Weathering of 134/137Cs following leaf contamination of grass cultures in an outdoor experiment.

After spraying grass cultures with rainwater collected after the Chernobyl reactor accident, the time-dependence of the weathering of leaf contamination of 134/137Cs was determined. Hereby the influence of rain and of biomass increase due to growth was considered. Two effective half-lives were found of 6 d and more than 60 d in rain-protected grass for the activity per area (corresponding to 8 d and more than 60 d when related to the activity per dry weight) and 2 d and 30 d in rain-exposed grass for the activity per area (3 d and 23 d when activity per dry weight is considered). These half-lives represent the initially rapid (for about 90% of the activity) and later slow (for the residual about 10%) decrease of the Cesium content in grass. They might be due to different weathering mechanisms whereby the translocation of the radionuclides from the leaf surface into the plant interior and the loss of wax particles might be of importance.