Pu isotopes and 137Cs in the surrounding areas of the former Soviet Union's Semipalatinsk nuclear test site

Field missions were sent to Semipalatinsk City and several settlements near the former Semipalatinsk nuclear test site to investigate the current radioactive contamination levels of the land coming from long-lived radionuclides. The soil was sampled at about 20 sites, including some settlements such as Mostik, Dolon and Chagan, forest and pasture areas, along the roads from Semipalatinsk City to Kurchatov City and to Korosteli settlement in the direction of the Altai District. The radioactivities of 137Cs, 238Pu and 239,240Pu as well as 240Pub/239Pu atomic ratios in the soil were determined by non-destructive γ-ray spectrometry and radiochemical separation followed by α-ray spectrometry and/or ICP-MS, respectively. The results showed a distinction of 137Cs and 239,240Pu inventories in soil depending on the site where we visited. While the overall 137Cs levels were as same as or slightly lower than the domestic global fallout level (3 x 103 - 7 x 103 Bq/m2), 239,240Pu levels at some sites were several to a few ten times higher than the domestic level (40-120 Bq/m2). The atomic ratios of 240Pu/239Pu in the soil were in the range of 0.024 - 0.125, which were significantly lower than the value of 0.18 commonly accepted for global fallout Pu. (author)