Current levels and distribution of 137Cs and Pu isotopes in soil on the Kazakhstan territory of the Kazakhstan-Chinese border. Semipalatinsk and Lob Nor nuclear test sites detonation

More than 100 soil samples were collected from 46 sites along roads and some settlements connecting Alma-Ata to Semipalatinsk City of the Kazakhstan-Chinese border and analyzed for 137Cs and Pu isotopes (238Pu,239Pu and 240Pu). The mean 137Cs inventory at each site was within the range of 1,000-3,000 Bq/m2 for most of the sites. The 239,240Pu concentration and its inventories were observed in the wide range of 0.18-2.6 Bq/kg and 28-677 Bq/m2, respectively. At the most northern sites in the areas studied, higher 239,240Pu inventories were found corresponding to the increase of 239,240Pu fraction which was not leached by hot digestion with conc. HNO3+H2O2. The 239,240Pu/137Cs activity ratios for the soil samples from the southern areas lie in the narrow range of 0.016-0.039 (most of data being 0.02-0.03), probably indicative of global fallout origin. On the other hand, a little or several higher ratios (0.05 to 0.22) were found for soil samples from the northern areas. These higher ratios demonstrate strongly that there was additional Pu input of local fallout due to the atomic explosions. From 240Pu/239Pu atomic ratios measured, contribution of local fallout 239,240Pu, probably from the SNTS, was found to be higher (60-86%) in the sites around the northern areas than the southern ones. The present data might serve not only as a current baseline information on distribution and contamination levels of the long-lived fallout radionuclides in the Kazakhstan areas of the Kazakhstan-Chinese border, but also as a aid of selection of control area for epidemiological projects. (author)