4. Cesium-137 mass and volume activities in terrestrial environments

Although the spatial heterogeneity of fallout from atmospheric testing of nuclear weapons and the Chernobyl accident has faded over the years, mainly due to the varying retention capacities of cesium-137 in soils, the mass and volume activities of this radionuclide in certain environmental components may still show spatially contrasting values today. Measurements clearly highlight areas where residual contamination from atmospheric testing of nuclear weapons and the Chernobyl accident remains high (hereinafter referred to as ZRE for "zones de rémanence élevée"). For example, in certain regions where caesium 137 surface activities exceeded 10,000 Bq.m ^-2 in May 1986, and where soils are conducive to the retention of this radionuclide, average mass soil activities can be 5 to 30 times higher than in the western two-thirds of the country. Similarly,...