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The study is aimed at the source-term reconstruction for the exposure of people to ionizing radiation who lived in 1949–1956 on the Techa riverside. It deals with the migration of γ-emitting nuclides (GENs), and specifically 95Zr and 95Nb, in the river system. It is known that 95Zr exhibits abnormally high sorption properties and is virtually completely and irreversibly sorbed onto bottom sediments (BSs) and suspended material already near the liquid radioactive waste (LRW) discharge site. Therefore, its further migration is possible only with the solid runoff. It was shown previously that the large-scale radioactive contamination of the river occurred in the relatively short period from July to October 1951, when the water flow rate in the upper section was varied from 8 to 30 m3/s. Under such water runoff conditions, the most contaminated BSs near the LRW discharge site undergo intense stirring-up (erosion), and the resulting suspensions are transferred with gradual sedimentation of the suspended material throughout the river stretch. After October 1951, when the LRW discharge into the river decreased by 2–3 orders of magnitude, the 95Zr distribution in BSs was determined only by the radioactive decay and transfer of suspended matters and saltation loads. Specific features of methods used in the 1950s for measuring the specific activity of the sum of β-emitting nuclides (BENs, AΣ, μCi/kg) and sum of GENs (МΣ, μg-equiv Ra/kg) are discussed. The use of the ratio RΣ = МΣ/АΣ as a criterion furnishes new information on the 95Zr activity concentration in BSs and allows picking out BS samples with prevalent contributions of 95Zr (МZr) и 95Nb (МNb) to МΣ from the whole set of the archive data. Analysis of the measured archive data on the specific activity of BS samples taken from different sections of the Techa River in 1952, 1954, and 1955 using the criterion RΣ = МΣ/АΣ allowed estimation of МΣ ≈ МZr + МNb and recalculation of these results taking into account the radioactive decay as of November 1, 1951. The results of MΣ measurements performed in 1952, 1954, and 1955 and converted to the level of November 1, 1951 appeared to be close, although the absolute activity level decreased by a factor of up to ~10 mln owing to radioactive decay. The 95Zr specific activity in the river BSs as of November 1951 remained virtually constant throughout the river stretch. These results provide a new approach to reconstruction of the external dose for the Techa riverside population. [ABSTRACT FROM AUTHOR]

The study is aimed at reconstruction of the parameters of the source from which the Techa River was contaminated in the period 1949–1956 and deals with the migration of γ-emitting nuclides (GENs), namely, of 95Zr and 95Nb, in the river system. The archive (1951) results of measuring the specific activity of the sum of β-emitting nuclides (BENs), AΣ (μCi/kg), in the soil and plants in the Techa riverside regions that are not flooded by floodwaters are analyzed. Analysis shows that the radioactive contamination of riverside territories is not associated with atmospheric discharges from the enterprise stacks and that the measurement results do not correspond to the commonly accepted views on the contamination distribution. In particular, contamination of the riverside soil and plants varied nonmonotonically with increasing distance from the river bank and along the river (spotty contamination pattern was observed), whereas the absolute values of BEN specific activities were constant throughout the territory within an order of magnitude. Furthermore, the depth distribution of BEN specific activities in soil up to 0.5 m was virtually uniform, and in some cases the activity increased with the depth. Finally, the plants had both external (on leaves) and internal (in roots) contamination, and in some cases the BEN specific activity in stems and leaves was lower than in roots. Presumably, the radioactive contamination of the soil and plants was determined by 95Nb and was due to entrainment of an aqueous aerosol from the river water surface with the wind. The model calculations explain all the unusual distribution patterns observed and allow estimation of the upper boundary of the mean (for summer 1951) 95Nb activity concentration in the river water. [ABSTRACT FROM AUTHOR]

The study is aimed at reconstructing the parameters of the source from which the people living in 1949–1956 on the banks of the Techa River were irradiated. It deals with the migration of γ-emitting nuclides (GENs) and specifically 95Nb in the river water. Some assumptions concerning the sources from which 95Nb got into the river water and its migration with the river flow were made previously. It was noted that the 95Nb sorbability is abnormally low and it is readily transported over long distances with the river water, whereas 95Zr, on the contrary, is efficiently taken up by bottom sediments already at the point of the liquid radioactive waste (LRW) discharge and can migrate only in the form of suspended material or bed load. It was noted that 95Nb could get into the river water both directly with the discharged LRW (external source) and via release from bottom sediments (BSs) after the 95Zr decay (internal source). It was assumed that, after October 1951 when the LRW discharge into the river was reduced by 2–3 orders of magnitude, the internal source became the main source of the 95Nb supply into the river water. This study additionally confirms the above assumptions. Archive results of daily measurements of the water specific activity in 1952 in the upper reaches of the Techa River are considered. The activity concentration of the sum of β-emitting nuclides (BENs), AΣ (μCi/L), was determined by measuring the β-particle count rate with an end-window counter, and that of the sum of γ-emitting nuclides (GENs), МΣ (μg-equiv Ra/L), by comparing the ionizing power of the test and reference (226Ra) sources. In determining the activity concentration of jth BEN, the β-radiation absorption coefficient in the layer of all the materials between the sample and the end-window counter, Kj, should be taken into account. Determination of the ratio Rj = Мj/Аj = mj/Kj, where mj is the gamma equivalent of jth GEN (μg-equiv Ra/μCi), was suggested for each jth GEN in the discharged LRW. Comparison of the experimental ratios RΣ = МΣ/АΣ with the corresponding calculated values, Rj = mj/Kj, furnishes new valuable information on the 95Nb concentration in the river water. In the first half of the year 1952, the 95Nb activity concentration in river water was more than 10 times higher than the AΣ values measured with an end-window counter (practically, the 95Nb activity was not detected). The main source of the 95Nb supply into the river flow was the release of recoil nuclei from the BS surface layer upon 95Zr decay (internal source). It decreased with time by an exponential law in accordance with the 95Zr half-life. The 95Nb activity concentrations in water at Metlino village and Nadyrov Most settlement (42 km downstream LRW discharge point) were virtually the same, confirming abnormally low sorbability of 95Nb. [ABSTRACT FROM AUTHOR]

The causes of the abnormally high mobility of 95Nb in Techa River water are discussed from the viewpoint of general niobium chemistry, specific features of its chemistry on the tracer concentration level, and mode of its supply into the system. [ABSTRACT FROM AUTHOR]