Cs-134 and Cs-137 vertical profile investigation of Danube delta

By using the gamma ray spectrometry the vertical profile of Cs-134 and Cs-137 distribution in cores collected from the Danube Delta (Matita Lake) has been investigated. Simultaneously, by X-ray diffraction, the core mineralogical composition has been determined. Experimentally obtained Cs-137 specific activity profile could be well correlated with the core mineralogical structure. From the experimental data, the following values of the diffusion coefficient have been calculated: D1=(0.12±0.04)g2 cm-4 y-1 for the first clay rich layer and D2=(0.4±0.12)g2 cm-4 y-1 for the next clay depleted layer. The sedimentation rate R=(0.15±0.05)g cm-2 y-1 and the total cesium inventory equal to (3.30±0.09)kBq m-2 as determined from the same profile confirmed a certain degree of isolation of Matita Lake related to the Danube main branches. The almost complete lack of the Cs-134 allowed to conclude that the Cs-137 sediment contamination is mainly due to the atmospheric nuclear test fallout. (author)