Some aspects of environmental radioactivity around the former Soviet Union"""s Semipalatinsk nuclear test site: Local fallout Pu in Ust"""-Kamenogorsk district

Abstract

The 137Cs, 238Pu and 239,240Pu activity concentrations were determined together with the atomic ratios of 240Pu/239Pu for the soil samples at 19 sites from the Ust"""-Kamenogorsk district, located more than 300 km east of the Semipalatinsk nuclear test site (SNTS). The mean areal deposition of 137Cs ranged from 1,500 to 4,100 Bq/m2. However, some hot spot-like areas showing high concentrations of 5,500–7,700 Bq/m2 were foundat some sites within the city. The 239,240Pu levels ranged from <50 to 510 Bq/m2, however most of them ranged between 120–200 Bq/m2. These levels are nearly the same as those around the Semipalatinsk City. At most of the sites within the city and its adjacent areas, both nuclides were found in the soil layers up to a depth of 30 cm. A fraction of 20–50% of 239,240Pu was not leached by hot digestion with concentrated HNO3 containing a small amount of H2O2. Generally, such tightly bound fraction showed a trend to decrease with increasing distance from the SNTS. The fraction of these radionuclides that were deposited in Ust"""-Kamenogorsk district from global and from SNTS fallouts have been determined using the 240Pu/239Pu atomic ratios in both Pu fractions: one which can be leached with hot HNO3 + H2O2 and another that is a non-leacheable for each soil layer of core samples. As a result a fraction of 21–80% (mostly 30–60%) of total 239,240Pu were found to be due to the local fallout of Pu from the SNTS debris. For 137Cs, the contribution (mostly 10–20%) of local fallout from the SNTS were estimated to be far lower as compared to 239,240Pu.