Vertical distribution of natural and man-made radionuclides in the soil profile is a decisive parameter when calculating the dose rate of gamma radiation in the air above the ground and the effective dose of external human exposure. The main purpose of this work was to determine vertical distribution of 137Cs in soddy-podzolic sandy and sandy-loam soils in forests and grasslands in the south-western districts of the Bryansk region in the remote period after the Chernobyl accident. In 2015–2016, soil cores were sampled in 7 virgin meadows and 13 forested areas to a depth of 20 cm. The cores were cut into horizontal layers 2 cm thick. The 137Cs activity in the samples was determined using a semiconductor gamma spectrometer. The activity concentration in samples of dry soil (n = 200) ranged from 6.35 Bq/kg to 83300 Bq/kg with an average of 4550 Bq/kg. In the meadows in three cases, the maximum activity concentration was determined in the uppermost layer. With increasing depth, the activity concentration decreased and reached a minimum in the deepest layers. A difference between the surface layer and the deepest layer was two to three orders of magnitude. The three other meadows showed a relatively uniform distribution of 137Cs in the upper 4–6 cm, followed by a decrease in activity concentration with an increase in depth. In one meadow area, a peak of the 137Cs activity was found at a depth of 4–6 cm. In the forest, the most typical (in 10 cases) was the presence of a pronounced maximum activity concentration of 137Cs in the uppermost layer. The experimentally obtained values of the 137Cs inventory in the upper 20 cm of soil at the surveyed sites ranged from 42 to 1940 kBq/m2. The values of 137Cs inventory positively and statistically significantly correlated with officially established levels of 137Cs surface ground contamination for the territory of nearby settlements. Vertical migration of 137Cs in the soil in the surveyed areas was mainly limited to the upper 10 centimeters. The layer on average contained 94% of the total 137Cs inventory. Less than 1% of the total 137Cs inventory was found in the deepest soil layer sampled (18–20 cm). The obtained 137Сs activity distributions were used to calculate kerma rate in the air at a height of 1 m above the ground at the surveyed sites. The air kerma rate ranged from 52 to 2240 nGy/h (on average, 807 nGy/h). The caesium-137 deposit in the upper 6 cm of soil determined about 95% and 90% of the air kerma rate in the forests and in meadows, respectively. Radioactive caesium, which migrated into the soil to a depth of more than 10–12 cm, gave a negligible contribution (less than 1%) to the gamma-radiation dose rate in the air. In practical terms, it indicates that the depth of soil sampling equal to 20 cm is currently quite sufficient to estimate the dose rate of gamma radiation in the air in virgin grasslands and in forests.

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Санкт-Петербургский научно-исследовательский институт радиационной гигиены имени профессора П.В. Рамзаева, Федеральная служба по надзору в сфере защиты прав потребителей и благополучия человека,

The article presents data on the radiation situation on the territories of the protected zones of peaceful nuclear explosions «Globus-2», «Agat» and «Rubin-1» based on the results of field studies in 2020. Peaceful nuclear explosions were conducted in the Arkhangelsk region for seismic exploration. The results of the radiation-hygienic state of protected zones and radiation safety in the territories adjacent to peaceful nuclear explosions are analyzed by the main indicators: the values of the ambient dose equivalent of gamma radiation, the identification of gamma-emitting radionuclides in situ by field gamma spectrometry, the specific activity of technogenic radionuclides in the soil and tritium in the water of reservoirs and drinking water sources. An assessment of the sanitary condition of the studied territories of protected zones of peaceful nuclear explosions is given. It was found that the levels of the ambient dose equivalent rate of the gamma radiation at all sites are at the level of fluctuations in the natural regional radiation background in the range of 0.08-0.20 microSv/h. On the territory of the protected zone of the peaceful nuclear explosion «Globus-2» were repeatedly identified areas of minor local soil contamination with 137Cs (the previous study was performed in 2011). Increased values of the ambient equivalent dose rate of gamma radiation (0.20 -0.22 μSv/h) and specific activity of 137Cs in two soil samples (154 and 160 Bq/kg, respectively) were found in these areas. The tritium content in the water of water supply sources does not exceed 5 Bq/kg. These values are typical for global levels of this radionuclide in water bodies. Remains of technological equipment were found on the territories of the protected zones of the peaceful nuclear explosions (especially in the protected zone of the explosion «Agat»), as well as rusty metal pipes and barrels, the remains of wooden structures, etc. Information signs installed on dilapidated concrete foundations at the mouths of combat wells of all surveyed peaceful nuclear explosions have subtle inscriptions. The presence of forest thickets in the places where the investigated peaceful nuclear explosions are conducted and their ignition during forest fires is a potential threat to the release of technogenic radionuclides during depressurization of the mouths of combat wells.

This paper continues the series of publications on evaluation of the consequences of the Fukushima-1 nuclear power plant accident and the impact of the emergency radionuclide discharges on the contamination of the sea biota and coastal areas of the Far-East regions. In autumn 2019, the fourth scientific expedition of the Russian geographic society on the monitoring of the radiation situation in Kurily-Kamchatka region was performed on the training vessel «Professor Khlyustin». The expedition included 9 specialists from noncommercial organization «Polar research Fund «Polar Fund», «Russian state hydrometeorological institute», «Radium institute after V.G. Khlopin» of the State Corporation «Rosatom», «Kurchatov institute», «SaintPetersburg research institute of radiation hygiene after prof. P.V. Ramzaev» and «Marine state university after admiral G.I. Nevelsky». The aim of the fourth expedition was to evaluate the radiation situation in the Sea of Japan and Kurily-Kamchatka region after the Fukushima-1 NPP accident as a continuation of the similar marine expeditions in 2011, 2012 and 2014. The survey was performed in the water area of the sea of Japan and Okhotsk sea. The results indicate that the concentration of 137Cs and 90Sr in sea water, hydrobionts, soil, ground and sea vegetation is still on the baseline level due to the global fallouts.