Study of the transfer of radionuclides in trees at a forest site

The transfer of radionuclides such as Cs-137 and Sr-90 from soil to trees (conifers) was studied in a forest area, the Boreon massif, 30 km north of Nice in South Eastern France. This area has been highly contaminated after the Chernobyl accident. Besides the gamma-emitting fission products, the alpha-emitters Pu-238 and Pu-239+240 and the pure beta-emitter Sr-90 were measured in different parts of the studied trees (roots, branches, twigs, etc.). As has already been reported by other authors, the radionuclide activities in the tree rings are not correlated with the fallout deposition. They were found varying according to the sap flux in the tree and higher in sapwood than in heartwood. For cesium the root absorption was found to be lower than the atmospheric deposition. Soil-to-plant concentration factors were calculated for Cs-137, Sr-90 and Pu-239+240.