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Cesium-137 in forest fruits
VRBOVÁ, Anežka
Significant artificial radionuclides occurring in the environment include Cs-137 from nuclear weapons tests that took place in the atmosphere during the 1950s and 1960s, and nuclear power plant accidents, such as at Chernobyl block 4 and crash at Fukushima. This bachelor thesis compares the amounts of Cs-137 and K-40 in different types of forest fruits, such as blueberries, raspberries and blackberries. Certain sites in Šumava were selected for their collection, where there was significant radioactive fallout after the Chernobyl nuclear power plant accident in 1986. Using semiconductor gamma-ray spectrometers, the specific activity of Cs-137 and K-40 was measured. All samples were measured in the dry state (dry matter). Cs-137 measurement values ranged from 1,143 Bq.kg-1 to 500 Bq.kg-1. For K-40 measurements, the values ranged from 166 Bq.kg-1 to 1280 Bq.kg-1. Differing values in individual localities are the result of uneven rainfall when the radioactive cloud passed over our territory after the Chernobyl disaster. However, there are also differences between species of forest fruits, which exhibit different accumulation properties due to different root system depths and their surrounding soil properties. The measured values were compared to the established limits and radiation sources found in our environment. The values measured are not high and compared to other sources of radiation are negligible, which has little impact on our health.
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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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