Preliminary evaluation of Cs-135/Cs-117 as a forensic tool for identifying source of radioactive contamination

Ratios of the fission products Cs-135 and Cs-137 were determined in soil and sediment samples contaminated from three different sources, to assess the use of Cs-135/Cs-137 as an indicator of source of radioactive contamination. Soil samples from the Chernobyl exclusion zone were found to have to be heavily depleted in Cs-135 (Cs-135/Cs-137 similar to 0.45), indicative of a high thermal neutron flux at the source. Sludge samples from a nuclear waste treatment pond were found to have a Cs-131/Cs-137 ratio of similar to 1, whereas sediment collected downstream from a nuclear reactor was highly variable in both Cs-137 activity and Cs-135/Cs-137 ratio. Comparison of these preliminary results of variability in radiocaesium isotope ratios with reports of Pu isotope ratios suggests Cs-135/Cs-137 Similarly varies with fuel and reactor conditions, and may be used to corroborate other methods of characterizing radioactive contamination. (c) 2007 Elsevier Ltd. All rights reserved.