The use of fallout 137Cs and 239,240Pu for dating of lake sediments |
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| Authors: | Timo Jaakkola Kimmo Tolonen Pertti Huttunen Soili Leskinen |
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| Institution: | (1) Department of Radiochemistry, University of Helsinki, Unioninkatu 35, SF-00170 Helsinki 17, Finland;(2) Department of Botany, University of Helsinki, Unioninkatu 44, SF-00170 Helsinki 17, Finland;(3) Department of Biology, University of Joensuu, P.O. Box 111, SF-80101 Joensuu 10, Finland |
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| Abstract: | The distribution of 137Cs and 239,240Pu in sediment core samples of the Finnish lakes Laukunlampi, Lovojärvi and Pääjärvi were determined. The sediment samples were collected using dry ice and liquid nitrogen freezing methods. The sediments of these lakes are annually laminated. A clear maximum concentration of 137Cs and 239,240Pu was found in sediment layers formed during 1962–1964, the years of maximum fallout, and the middle of the 1950's can be estimated from the 137Cs and 239,240Pu profiles. The highest concentrations, 11 500 and 820 pCi kg–1 dry wt for 137Cs and 239,240Pu, respectively, were found in the sediment of Laukunlampi. The vertical distribution was similar for 137Cs and 239,240Pu in the lakes investigated. A slight migration of 239,240Pu and 137Cs was found and the migration of 137Cs seems to be higher than that of 239,240Pu. The advantages of 137Cs dating method are rapidity and simplicity. 239,240Pu is preferable when the sample size is small. The agreement found between 137Cs and 239,240Pu dates and the annual laminae show that these fallout radio isotopes can be used for dating sediments formed during the past 25 years. |
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| Keywords: | paleolimnology dating radioactive fallout sediment 137Cs 239 240Pu varves |
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