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Caesium-137 is one of the major artificial radioactive elements, whose sources are atmospheric nuclear tests carried out in the 20th century and nuclear power plant incidents such as Chernobyl. Because of uneven precipitation, there were significant differences in radioactive fallout levels in different areas of the Czech Republic during the passage of the radioactive cloud from Chernobyl. Due to the high solubility of Caesium-137 in water and easy distribution in the environment, there is contamination of the lower soil levels where the plant root systems are located. The aim of this work is to collect soil samples from selected localities, where in 1986 significant contamination was detected as originating from Chernobyl, determination of their Caesium-137 content by gamma semiconductor spectrometry and comparison depending on the type of soil. The research question was set as: Does Caesium-137 content differ in different soil types? As part of this study, samples of uncultivated agricultural land and forest land were collected from layers 0-5, 5-10 and 10-15 cm in Kvilda, Zadov and Churanov. For comparison, results were also collected from a locality where the radioactive fallout was not so significant. This locality is around the village Straz nad Nezarkou, which is found on the protected nature reserves of Trebon. From the results of measuring the soil it was found that even after thirty years since the Chernobyl disaster occurred, Caesium-137 is still found in the upper layers of soils, specifically to depths of 5 cm. The highest specific activity of Caesium-137 was measured in the forest soils in Zadov at depths of 0-5 cm (364 Bq.kg-1) from the total range of all samples, 2,24 Bq.kg-1 to 364 Bq.kg-1. The highest specific activity of potassium K-40 was measured in uncultivated agricultural land in the locality of Kvilda at depths of 0-5 cm (883 Bq.kg-1).

The first part of thesis is engaged in explanation of some basic concepts regarding an elected topic: radioactivity, isotope, nuclide, halftime, gamaspectrometry etc. In the second part I deal with element cesium and influence of the Chernobyl accident. The final part processes questions of cesium - 137 in wood ecosystem. It is mainly concerned with research and gamaspectrometric measurement of wood substance, bark and samples of soil. In practical part (it is one part of the final part) I made taking of samples (especially soil from the depth 0-5 cm, soil from the depth 5 - 20 cm, wood substance and forest planting) from some localities above all the South Bohemian Region and next their gamaspectrometric measurement (quantitative analysis of cesium - 137 in wood ecosystem) at SÚJB in České Budějovice according to methodology.Measured values of cesium - 137 in samples were relatively low and its impact on the health of our population is in regard to other sources of ionizing radiance insignificant. The supposed hypothesis was herewith confirmed.