|
|
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.
|
guest ::
