Cesium in Europe beforeChernobyl
Legacies of the Cold War, the main radioactive contaminations remaining 40 years after the cessation of atmospheric nuclear tests are due to cesium-137 and to a lesser extent, strontium-90, two radioactive nuclei with half-lives of about thirty years. The map shows the distribution of Cesium-137deposits in Europe, just before the Chernobyl accident in 1986. Ground contamination was around a kilobecquerel per square meter. On that date the contamination was divided by about two from the years1950-60.
Atlas of Chernobyl