First results on 236U levels in global fallout

The global fallout U-236 level in soil was deduced from measurements of U-236, Pu239+240 and (CS)-C-137 in surface soils which are solely influenced by global fallout A total of 12 soil cores from the depths of 0-10, 0-20 and 0-30 cm were collected at a flat forest area in Japan. Concentrations of Pu239+240 and U-238 were determined by alpha-particle spectrometry. while the U-236/U-238 ratio was measured with accelerator mass spectrometry (AMS). Consistent U-236/Pu-239 ratios between 0.212 and 0.253 were found. Using this ratio, the total global fallout of U-236 on the earth is estimated to be as much as ca. 900 kg. This knowledge will contribute to the promotion of research on U isotopes, including U-236, for the fields of geo-resources, waste management and geochemistry. (C) 2009 Elsevier B.V. All rights reserved.