|
|
The contents of caesium-137 in different soil types in selected locations in CR
ČADOVÁ, Michaela
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).
|
|
|
Comparison of the measured specific activities of cesium 137 in different species of bryophytes.
TRNKOVÁ, Michaela
This bachelor thesis focuses on measuring specific activities of Cs-137 in different species of moss in areas affected by radiation fallout and compares the species different tendencies to absorb radionuclides. The research question is: Do different species of moss in areas affected by radiation fallout contain different amounts of Cs-137? The theoretical part of the thesis introduces the radiobiological problematics, including basic terms and units, and its contemporary situation. This part also focuses on radionuclide Cs-137 and its sources and kinetics in nature. The practical part describes used methodology and consequently focuses on the results of measuring chosen moss samples, including their subsoils. Specialised literature describes mosses as significant bioindicators of radionuclides. This thesis tries to distinguish different species and establish whether those different species have different tendencies to absorb radionuclides. The locations for sampling were chosen according to previous studies which located areas with high concentration of Cs-137 caused by radiation fallout in 1986. The total amount of moss and subsoil samples is 20 samples each. One of the locations was Russian island Valaam in Ladoga Lake where four samples were collected. Specific activity was measured using semiconductor gamma spectometry. Beside Cs-137, the focus was on concentration of natural radionuclide K-40. Measured spectra were evaluated by GAMWIN software. Measuring specific activity of Cs-137 in moss and subsoil samples and calculation of transfer ratio proved that different species of moss in areas affected by radiation fallout contain different amount of Cs-137.
|
|
|
Contents od caesium-137 in mushrooms
ČADOVÁ, Michaela
The aim of this work is to compare the presence of Cs-137 in different kinds of mushrooms in selected locations using semiconductor gamma-ray spectrometry. Research question was determined: Does Cs-137 content amount vary depending on the fungal species? The first part deals with basic knowledge of ionizing radiation, which is important for the complex understanding of thematic problems. This concerns basic radiobiological terms such as radioactivity, ionizing radiation, its biological effects and basic units and quantities used in radiobiology and radiation protection. Further I deal with the above mentioned measured radionuclide Cs 137, which resources in our country include the Chernobyl nuclear plant accident and tests of nuclear weapons in the 20th century. I also pay attention to this element in the cycle of nature, its distribution in the body and the effects on our environment. Shortly I even deal with basic knowledge of the Cs-137 accumulation in mushrooms. Another point mentioned is the research methodology, a brief introduction to semiconductor gamma spectrometry. As sampling sites I selected Zadov, Churáňov and Kvilda in Šumava, where in 1986 there was detected the biggest radiation fallout. For comparison, I also measured samples of mushrooms from localities of less significant fallout. These are sites around a village of Příbraz and in the woods of Jemčina within Třeboň region. A total of 26 mushroom samples were taken. Mass activity was measured by semiconductor gamma spectrometry in the Regional Center of the State Office for Nuclear Safety in České Budejovice. In addition to Cs 137 there was also measured a content of a natural isotope Potassium-40. It is a Cs 137 chemical homologue, which has similar properties and is present homogeneously throughout the whole ecosystem. For comparison I also measured mass activity of other forest ecosystem components such as moss, bark, cones and ground. Measuring time of the mushroom samples was for about 24 hours. The other forest ecosystem components measuring time ranged from 24 to 48 hours. The measured spectra were analysed by using the GAMAT software tool. The highest measured mass activity of Cs-137 was detected in a pine bolete sample from the site of Churanov in Sumava (4 265 Bq.kg-1). Also Russula emetica from Zadov shows relatively high activity (3 050 Bq.kg-1). The smallest amount of Cs 137 was measured in Cystolepiota high, originating in the locality of Jemčina in Třeboň region (5.6 Bq.kg-1) and in a sample of Lactarius volemus from the nearby village Příbraz (34.7 Bq.kg-1). The highest mass activity of natural radionuclide K-40 was measured in a sample of blusher from the village Příbraz site (4 329 Bq.kg-1). High value was probably caused by the use of fertilizers or pesticides near this sample. Large number of K-40 was also seen in Laccaria amethystina, also coming from the village Příbraz (2 901 Bq.kg-1). On the contrary, the least of this element was found in Cystolepiota high sample from Jemčina forests (971.8 Bq.kg-1) and in Lactarius volemus from Příbraz (999,6 Bq.kg-1). According to the measured values, we can conclude that the measured mass activity differs a lot. Individual sites may have different values because of uneven rainfalls in our country at the time of the radioactive cloud passage after the Chernobyl explosion. However, specific species of fungi from the same sites differ, which is due, inter alia, to soil characteristics and mycelium depth. The results correspond to the fact that the mushroom-shaped fungi show a greater amount of Cs-137 unlike gilled fungi presented as well by other authors.
|
|
| |
|
|
Cesium 137 in wood ecosystem
KAŇKOVÁ, Jaroslava
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.
|
guest ::
