Intercomparison and Validation Exercises in the Southern Urals and the Kazakh Polygon

Abstract


The military nuclear activities in the former Soviet Union led to unique contamination and resulted in high cumulative exposures. A proper assessment is needed for mitigation and for the further development of radiation protection. Environmental samples from areas affected by large radioactive releases into the Techa river starting in 1948 and by fall-out from the explosion of a tank containing high level waste in 1957, were independently analysed by two Russian groups and by our team in 1992-93. Soil, sediments, milk and fish samples were split into three aliquots and analysed for ⁹⁰Sr,¹³⁷Cs and plutonium. Soil values in areas accessible to the local population were up to 16 kBq kg^-1 for ⁹⁰Sr, up to 26 kBq kg^-1 for ¹³⁷Cs and up to 12 Bq kg^-1 for ²³⁹Pu, respectively. Milk generally contained low levels ranging from <1 to 25 Bq kg^-1 for ⁹⁰Sr, 1 to 14 Bq kg^-1 for ¹³⁷Cs and <0.1 Bq kg^-1 for plutonium. Pike from the Techa river, however, showed15,000 Bq kg^{-1 90}Sr. In 1993, 750 in vivo measurements of ⁹⁰ Sr/⁹⁰Y were performed in individuals of communities situated downstream of Majak which had incorporated large activities of ⁹⁰Srfrom using the Techa river as drinking water supply. To help validate a large body of Russian measurements, a transportable body counter which measures the scull content of ⁹⁰Sr/⁹⁰Y directly from high energy β's emitted from the front of the head and also indirectly via Bremsstrahlung was developed. Although the highest activities (37 kBq) were found in persons having lived at the river Techa during the early releases, considerable ⁹⁰Sr contamination, often accompanied with elevated ¹³⁷Cs burdens, were also found in younger persons indicating recent ingestion. Chronic and recent contamination will add to the uncertainties involved in the assessment of bone marrow doses from ⁹⁰Sr as a crucial element in dose reconstruction for the Techa river cohort. A first visit to the medical school and health institutions in Semipalatinsk and to a village having been heavily contaminated by an atmospheric bomb test at the Polygon yielded sometimes contradictory information but indicated high cumulative exposures in several Kazakh settlements adjacent to the test site.