Statistical characteristics of the activity concentration in the surface layer of the atmosphere in the 30 km zone of Chernobyl

Series of measurements of the daily average activity concentrations of 137Cs and 144Ce in the atmospheric surface boundary layer in the 30 km zone around the Chernobyl Nuclear Power Plant are discussed with regard to their statistical characteristics. A high level of fluctuation in the specific activity concentration was found with maxima exceeding the annual average by a factor of 10–20 and lasting up to 14 days. During the years 1987–1991 the absolute values of the fluctuations decreased with time. The decrease of the activity concentrations was found to be higher than that due to radioactive decay alone.