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 241Am in soil varies from <0.3 Bq/kg to 390 Bq/kg, with an average value of 5 Bq/kg; for 137Cs 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 (241Am to 920 Bq/kg and 137Cs to 12150 Bq/kg).

Transfer parameters of radionuclides from soil to plants at the area of craters produced by underground nuclear explosions at the Semipalatinsk test site.

A study to determine 137Cs, 90Sr, 241Am, 239+240Pu radionuclides in vegetation cover of the area of craters produced by underground nuclear explosions at the Semipalatinsk test site (STS) is summarised in this paper. Transfer factors (Tf) required for the quantitative description of the radionuclides transition from the soil to aboveground plant parts were found to be highest for sagebrush (Artemisia sublessingiana), Tf values for 90Sr were gradually decreasing with increasing distance from the dump zone. When arranging the radionuclide transferring factors in descending order, the following sequence was obtained: 90Sr Tf > 137Cs Tf > 241Am Tf > 239+240Pu Tf, which is consistent with International data. All Tf derived are much higher than those ones derived earlier for epicenters of aboveground nuclear tests and are closest to values for conventionally "background" areas at the Semipalatinsk test site.