~(137)Cs, ~(239,240)Pu and ~(241)Am in bottom sediments and surface water of Lake Paeijaenne, Finland

摘要

The concentrations and vertical distribution of ~(239,240)Pu, ~(241)Am and ~(137)Cs in the bottom sediments and water samples of Lake Paijanne were investigated. This lake is important, since the Paijanne area received a significant deposition from the Chernobyl fallout. Furthermore Lake Paijanne is the raw water source for the Helsinki metropolitan area. In addition no previous data on the distribution of plutonium and americium in the sediment profiles of Lake Paijanne exist. Only data covering the surface layer (0-1 cm) of the sediments are previously available. In the sediments the average total activities were 45 ± 15 Bq/ m~2 and 20± 7 Bq/m~2 for ~(239,240)Pu and ~(241)Am, respectively. The average ~(241)Am/~(239,240)Pu ratio was 0.45 ± 0.14. The ~(241)Am/~(239,240)Pu ratio is lowest in the surface layer of the sediments and increases as a function of depth. The ~(238)Pu/~(239,240)Pu ratio of the sediment samples varied between 0.012 ±0.025 and 0.162 ± 0.079, decreasing as a function of depth. The average activity in water was 4.9 ± 0.9 mBq/m3 and 4.1 ±0.2 mBq/m~3 for ~(239,240)Pu and ~(241)Am, respectively. The ~(241)Am/~(239,240)Pu ratio of water samples was 0.82 ± 0.17. ~(239,240)Pu originating from the Chernobyl fallout calculated from the average total activities covers approximately 1.95 ±0.01% of the total ~(239,240)Pu activity in the bottom sediments. The average total ~(137)Cs activity of sediment profiles was 100 ± 15 kBq/m~2 and 19.3 ± 1.4 Bq/m~3 in water samples.