Characterization of area radioactive contamination of near-surface soil at the Sary-Uzen site in the Semipalatinsk test site

The paper provides study of the radioactive contamination of near-surface soil at the Sary-Uzen site in the Semipalatinsk test site (STS). Increased values of natural radionuclides in the studied area were not detected, which indicates the absence of possible geochemical anomalies that could create an elevated radiation background. Radioactive contamination by technogenic radionuclides is caused by two factors. The first factor is fallout of radioisotopes from the atmosphere because of an explosion on September 24, 1951 at the "Experimental field" site. The fallout plume extended from the north-western part of the site to the very south. The range of activity concentration values for Am-241 in soil varies from <0.3 Bq/kg to 390 Bq/kg, with an average value of 5 Bq/kg; for Cs-137 from <1.1 Bq/kg to 330 Bq/kg, with an average value of 55 Bq/kg. A second, but more significant factor is the fallout of radioisotopes due to underground nuclear tests with radioactive release that took place in boreholes on the site itself. The largest area of contamination (about 8 km) is the fallout from testing borehole No. 101 (Am-241 to 920 Bq/kg and Cs-137 to 12150 Bq/kg).