RADON-222 DISTRIBUTION IN THE SOILS OF THE FLOODPLAIN AND FLUVIAL TERRACES ABOVE FLOODPLAIN OF THE IRTYSH AND TOBOL RIVERS

The relevance of the obtained data on distribution in the soils of the natural radionuclide – radon-222, which contributes to the key radiation load for lung cancer development, are relevant as regional indicators for the Tyumen region in assessing the potential radon danger of soils. The main aim of the research is to consider interrelation of physical parameters of soil (temperature, depth) and atmospheric air (temperature, humidity, pressure) with radon-222 flux density in soil, to define potentially radon dangerous sections of soils in flood plains and above flood plain terraces of the Irtysh and Tobol rivers. Objects: radon-222 flux density in soils of floodplains and above floodplain terraces of the Irtysh and Tobol rivers within Tobolsk, Vagaysk and partially Yarkovo districts of the Tyumen region of the Russian Federation. Methods. Radon-222 density in soil was measured by passive sorption of radon-222 on activated carbon with further measurement of activity of sorbed radon-222 in laboratory conditions by means of complex «Camera-01». Radon-222 activity in coal was measured by β-radiation of short-lived decay products of radon – lead-214 and bismuth-214 which are in radioactive equilibrium with radon-222 sorbed in coal. Results. The paper introduces the data (2018–2021) on radon-222 flux density distribution in soils of floodplains and fluvial terraces above floodplain of the Irtysh and Tobol rivers within the boundaries of Tobolsk, Vagaysk and partially Yarkovsky districts of the Tyumen Region of the Russian Federation. Radon-222 flux density from the soil surface does not exceed 80 mBq/(m2·s) in 73 out of 76 investigated plots of soils, located in the floodplain and fluvial terraces above floodplain of the Irtysh and Tobol rivers which corresponds to the first radon hazard class according to Basic Sanitary Rules for Radiation Safety (BSRERS 99/2010), approved in the Russian Federation. The surface of the soils of these sites is not potentially dangerous. Radon-222 flux density at soil depth of 0,4–1,0 m averages 109,3…495 mBq/(m2·s), maximum values vary within the limits of 1085...1280 mBq/(m2·s). The reliable influence of soil depth on distribution of radon-222 flux density was detected – radon-222 concentration decreases from the depth to the soil surface. Radon-222 flux density does not depend on insignificant variations in atmospheric pressure, no statistically significant relations with temperature and atmospheric air humidity were established. The average values of radon-222 flux density in soil in summer (August) and autumn (September) months increased nearly twice as much as in spring (May)