Analysis of the temporal evolution of atmospheric Be-7 as a vector of the behavior of other radionuclides in the atmosphere

The mean weekly levels of Be-7 in the atmosphere of Caceres (Spain) was measured for three consecutive years, from 1992 to 1994. The values showed a strongly seasonal behavior, conditioned fundamentally by two effects: (1) the incorporation of Be-7 into the low layers of the troposphere due to the displacement of masses of air from higher layers caused by the solar irradiation, and (2) the washing of Be-7 out of the atmosphere by rain. From the quantification of these two effects, the residence time of Be-7 was determined in die atmosphere at ground level as 10.3 days, with an interval for the standard error of 9.0 and 12.1 days. Modelling the temporal evolution of this radionuclide we were able to explain 90.72% of the variance of the measured activity levels. Using the effective residence time of Be-7, we were able to justify the diversity of values obtained for the deposition of Cs-137 in different soils of the province of Caceres due to the fallout from atmospheric nuclear blasts.