Dating of a sediment core from Lake Biel (Switzerland) and source characterization of fallout Pu

A sediment core from Lake Biel was dated by means of the naturally occurring radioactive isotope ²¹⁰Pb as well as by the anthropogenic isotope ¹³⁷Cs. The latter one can be detected as radioactive fallout of certain events in the sediment layers and accordingly be correlated with a distinct date. A verification of the correlated events is accomplished by particular isotope ratios of the anthropogenic isotopes ²³⁸Pu, ²³⁹Pu and ²⁴⁰Pu as well as ²⁴¹Am as a decay product of the short-lived ²⁴¹Pu. Furthermore, the percentage of the total ¹³⁷Cs fallout was calculated corresponding to the specific events.