The influence of trees on contamination of soil with 137Cs

Nuclear weapons testing in the atmosphere and accidents in nuclear energy facilities in the last 50 years caused significant contamination of the environment. Half-life of certain leaked radionuclides is several decades and therefore they are still present in today's environment. That is the reason why there is still on going monitoring of radiation situation in the Czech Republic in order to determine the behaviour and kinetics of anthropogenic radionuclides in the environment and the severity of radiological impact on humans. The results of this monitoring serve to review the radiation situation, observe long-term trends and last but not least to gain new knowledge that could facilitate the management od radiological emergencies. The aim of this thesis was to measure the content of 137Cs in soils under and around leafy tree crowns in the area affected by radiation fall and to find out whether the tree's crown has an effect on the distribution of 137Cs in the soils below them. To this end, a research question has been set: Do tree crowns affect the distribution of cesium in the soils below them? For better intelligibility, the introduction of the thesis is devoted to information about ionizing radiation, basic terms and quantities in the field of ionizing radiation, sources of radionuclide contamination, especially the Chernobyl nuclear power plant accident, environmental and population contamination, and elements important for the practical part of this work. The theoretical part is followed by research methodology. The soil samples were collected under five leafy trees of the Walnut species that met the set criteria for collection. Under each tree, samples were taken in three directions at an angle of 120° always at the trunk, in the middle of the crown, at the edge of the crown and outside the crown. Thus, 12 samples per tree, a total of 60 samples. Dry and purified soil samples were measured by semiconductor gamma spectrometry which determined 137Cs radionuclide mass activity values as well as naturally occurring radionuclide40K. Graphs were generated from the measured values. Despite the frequent deviations that may be caused by natural phenomena or human activities, it was found out that tree crowns affect the distribution of 137Cs in the soils below them