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Vertikální migrace Cs-137 v půdním profilu do hloubky 1m
NOVÁČKOVÁ, Jana
From the point of view of long-term environmental contamination, cesium-137 is the most important element because it is absorbed into the human body, but also into the root system of plants, mosses, fungi, wild berries and wild game meat. Above all, however, it remains in different layers of the soil. Several main factors affect the distribution of radionuclides in the soil, namely rainfall, water entry into the soil, diffusion, migration through root systems, human, animal activity, etc. Monitoring its occurrence in the environment is important and involves the interference of cesium-137 with potassium. It in absorbed in the human body (about 80%) and excreted in the urine. It remains most in soft tissues and its biological half-life is 110 days. We are exposed to ionizing radiation from natural sources and human activities. Human activity causes artificial radioactivity, which is relatively small, compared to natural radioactivity, but the impact on human health can be huge. The first part of the bachelor thesis relates to the issue with the use of theoretical and scientific information, standards, law. The next part includes the methodology and results of practical measurement of soil samples. The aim was to find out which layer of soil deposits the most radioactive cesium, because it is assumed that it is still a part of it. Soil samples were taken in the protected landscape area of Šumava, in the 2nd zone of the National Park, in the Železnorudsko area, locality Nová Hůrka (Kuchyně). The site choice presented the distribution of radioactive fallout in our territory. Soil samples were take in 1 cm increments to a depth of 1 m, dried, cleaned and prepared for measurement. The samples taken were measured in the standard way at the Regional Center of the State Office for Nuclear Safety (SÚJB) in České Budějovice. The spectra obtained by measurement were evaluated using GAMWIN software. In the practical part, soil layers with a thickness of 1 cm to a depth of 1 m were taken and after their processing and preparation for measurement, the activity of cesium-137 in soil samples was measured by semiconductor gamma spectrometry. The measured results were compared with the results of previous soil samples and they were evaluated and interpreted in the bachelor's thesis. The results of the measurements showed the depth to which the maximum of cesium-137, which comes from nuclear weapons testing, and especially from the radiation accident at Chernobyl, is currently located. The aim of the work was to find out what is the depth distribution of cesium-137 in uncultivated soils and whether its migration through the soil profile is still ongoing and to confirm or refute the hypothesis of what maximum amount still occurs in the range of plant root system.
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Content of cesium-137 in forest ecosystem in selected locations
SEBEROVÁ, Pavlína
The human and the whole environment are irradiated from the different sources (natural or artificial). The natural sources of radiation are cosmic and sun rays or the natural radiation of the Earth. The artificial sources mean cyclotrons, X-rays, particle accelerators, nuclear reactors and others. Natural cesium is located very rarely on Earth, but it has many artificial isotopes (for example Cs-137 and Cs-134). The Cs-137 is an artificial isotope produced by human. The first source of the Cs-137 became the nuclear tests and attacks used in the World War Two. In the 1960s (related a study of nuclear weapons) there were found out storing of Cs-137 in the surface soil layers. Even the peaceful use of the nuclear energy could cause the nuclear crash accompanied by a leakage of radioactive substances. The most tragic crash was an explosion of the nuclear power station Chernobyl in Ukraine. That crash contaminated the whole Ukraine and close states, but also Scandinavia. The spread of the Cs-137 depended on the rainfall and the air flow. Human has been affected by the radioactive elements even after the long time since the crash. Forest ecosystem seems to be the place with the largest amount of Cs-137 located. The Cs-137 may get into the human body though food; it has a very long half-time (30ys), it is stored in the top soil layers and through the root system of plants gets into the plants or mushrooms. The aim of this thesis is to determine and compare the content of the Cs-137 in the selected commodities in the forest ecosystem of Šumava using semiconductor gamma spectrometry. The research question was specified: Is the content of the Cs-137 in the selected commodities of the Šumava forest area significantly different? Based on an analysis of literature and consultation with the State Office for Nuclear Safety there were chosen areas, where was the highest fallout of radioactive elements. Therefore I sampled the area called Kvilda, Zadov and Churáňov. Further locations with the commodities of the forest ecosystem are Bavorov, Svinětice and Baranaviči. There are samples of soil, moss, spruce bark, cones and lichen. Not all commodities could be collected in all locations because there were picked in a small area and not all commodities occurred there. To determine the mass activity of the Cs-137 samples I used a semiconductor gamma spectrometry. The obtained spectra were evaluated through software GAMAT. The range of the values of mass activity of the Cs-137 in all samples is between 3-700 Bq.kg-1. The highest activity was measured in soil, where values reached up to 700 Bq.kg-1. High activity was also measured in moss in Kvilda, 513 Bq.kg-1. Samples of spruce bark, cones and lichens have low values activity. It was not reached out the value of 300 Bq.kg-1. Answer to the research question is that contamination of Sumava Cs-137 in selected commodities forest ecosystem is significantly uneven.
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