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).

90Sr/137Cs ratios in soil of epicentral zones of «Experimental Field¼ testing site of Semipalatinsk Test Site.

The paper presents the results of 90Sr/137Cs isotopic ratios in the soil surface layer in the venues of surface and atmospheric nuclear tests at the territory of the «Experimental Field ¼â€¯site of the Semipalatinsk Test Site. One of the main factors in the radiation impact of a nuclear explosion on the environment is the decay of fission products. The determination of 137Cs activity in soil is carried out by accurate, rapid and sufficiently cheap gamma-spectrometric method, while the existing methods of determining 90Sr activity are quite problematic: they either have sufficiently high detection limits or are time-consuming. As an alternative method, 90Sr activity can be determined using its correlation dependence with 137Cs activity. According to the literature, each test has its own fission product ratio, depending on the nuclear charge. As a result of the conducted research it was revealed that one epicenter is located at the technical site P-1, the ratio of 90Sr/137Cs is equal to 4,8; at the technical site P-3 - 2 epicenters, the ratio of 90Sr/137Cs is equal to 0,8 and 0,9; at the technical site P-5 - 6 epicenters, the ratio of 90Sr/137Cs is in the range of 0,9-2,1; at the technical sites P-2, P-7 - 19 epicenters, the ratio of 90Sr/137Cs is in the range of 0,6-2,1. It is assumed that the differences in the value of fission product ratios are due to different types and capacities of nuclear charges, as well as different explosion altitudes. The obtained ratios allow to calculate 90Sr by 137Cs activity in soil of the epicentral zones at the territory of the «Experimental Field ¼â€¯testing site by the computational method.