35 years have passed since the Chernobyl NPP accident, 10 years – since the «Fukushima-1» NPP accident. At the present time extensive activities on the remediation of the consequences of two major large-scale radiation disasters are performed in the Belorussia, Russian Federation, Ukraine, and Japan. Releases of radiologically significant radionuclides after the Chernobyl NPP accident correspond to 14 exaBecquerel – higher up to an order of magnitude compared to 3 emergence power units of the «Fukushima-1» NPP. The significantly lower release rate and deposition of 80% of the radionuclides released into the atmosphere on the surface of the Pacific Ocean lead to lower up to several orders of magnitude radioactive contamination of the Japanese territory compared to the territories of the former USSR and neighboring countries after the Chernobyl NPP accident. Collective dose to the public due to the Chernobyl NPP accident is higher up to several orders of magnitude compared to the dose to the Japanese population after the «Fukushima-1» accident. No statistically reliable long-term medical consequences are expected for all groups of the Japanese public, additionally exposed due to «Fukushima-1» accident. 134 emergency workers have developed acute radiation sickness due to the Chernobyl NPP accident. Emergency workers with doses higher than 150 mSv had increased radiation-induced morbidity with leukemia and solid cancers. Among the individuals, that were kids or adolescents in the exposure period after the Chernobyl NPP accident and residing on the territories of Belorussia, Ukraine and four most radioactively contaminated regions of the Russian Federation, morbidity with thyroid cancer is increase by a factor of 10 compared to the pre-accidental levels. The following lessons of the Chernobyl NPP and «Fukushima-1» NPP can be derived: faults in the NPP design and lack of response after the recognition of the faults; lack of timely full-scale prophylactic with iodine; unjustified resettlement of the residents of the radioactively contaminated territories several years after the accident.

To ensure the quality assurance of CT-examinations, it is necessary to obtain the high-quality diagnostic information and maintain the optimal exposure levels of patients and medical staff. This paper is focused on the requirements and main aspects of quality assurance of CT-examinations, which include quality control of the equipment, methods of CT-image quality control, optimization of radiation protection, as well as management of the unintended and accidental medical exposure. The paper contains recommendations on quality control of diagnostic equipment, methods for monitoring the quality control of CT-images, values of diagnostic reference levels for the detection of abnormally high patient doses and optimization of the radiation protection of patients, as well as the recommendations for management of radiation and non-radiation accidents. All main sections of the paper represent an unified quality assurance system in computed tomography.

In April 2020 we commemorate the 90th birthday of the major scientist, doctor of technical sciences, Professor Eduard Mechislavovich Krisiyk. A new field of research on radiation-hygienic assessment of the natural sources of ionizing exposure and limitation of the public exposure has been developed under his scientific supervision and personal participation. For the first time in the international practice E.M. Krisiyk as the main author developed the requirements for the concentration of the natural radionuclides in the building materials; as the co-author – in phosphoric fertilizers, indicated the necessity of their radiation control. His scientific results were included into various Russian legislative and methodical documents: Federal state law “On the radiation safety of the public” in 1996, Norms of the radiation safety NRB-96 and NRB-99, Basic sanitary rules on the provision of the radiation safety OSPORB-99, Federal targeted program “Radon”, various guidelines. His scientific school, his flock and followers are successfully developing the scientific-methodical basics of the regulation of the natural exposure of the public of the Russian Federation at the current stage.

A lack of accessible information about the demand for domestic articles on the mitigation of consequences of the accident at the Chernobyl nuclear power plant in the early post-accident period necessitates referring to publications presented in international bibliographic databases, which can be a good help in planning research and preparing publications. The intention is an analysis of articles in the field of eliminating the biomedical consequences of the Chernobyl accident in the world and in Russia, indexed in the Scopus database in 1986–2018. A search query gave an array of 3929 articles in Scopus. The largest number of articles was published by authors from the USA (13.2%), Ukraine (12.6%) and Russia (12.2%). A significant number of articles were published by international authors. The average annual number of articles was (119±6) in the whole array and (15±2) in the Russian array. In the whole array, 11.5% of the articles dealt with the biomedical problems of the liquidators of the consequences of the Chernobyl accident; 12.5% – the population living in the radioactively-contaminated territories; 18.7% – neoplasms; 8.6% – medical radiation physics; 21.2% – radioecology; 12.0% – biochemistry, genetics and molecular biology. In the Russian array, these respective percentages were 19.8, 17.3, 18.1, 21.7, 18.8% and 10.2%. On average, there were 10.5 citations per article, 70% of the articles were at least once cited, self-citations made up to 17.6%, and the Hirsch index was 81. A quite high demand for articles in the field of eliminating the biomedical consequences of the Chernobyl accident has been revealed among the world scientific community. Russian scientists should form a habit of quoting articles from their colleagues more often. Some domestic magazines still have a low publishing culture. A lack of transliterated lists of references not only precludes from indexing articles in Scopus, but also interferes with citing research papers from domestic scientists, their affiliated research institutions, and Russia as a whole.

The aim of this work is to assess the radiogenic risk of solid cancers incidence in the members of the Urals Childhood Exposure Cohort. The cohort includes people exposed under 20 years of age as a result of two radiation accidents at the Mayak Production Association in the Southern Urals (discharges of radioactive waste into the Techa River and the formation of the East Ural radioactive trace). The number of the cohort for solid cancer incidence analysis is 31,578 individuals. All the members were postnatally exposed and some of them – in-utero. Some of their parents were exposed before conception. 2,018 solid cancers were registered on the incidence catchment area during the period 1956-2018, the total amount of person years was 818,083. The analysis was carried out by the Poisson regression method with a simple parametric excess relative risk model. 95% confidence intervals were estimated with maximum likelihood approach. Only a postnatal dose was used in the first solid cancer incidence analysis of this cohort members with due account for preconception exposure of parents. TRDS-2016 mean postnatal dose accumulated over the entire follow-up period in the stomach of cohort members was 0.047 Gy. The analysis showed linear dependence of solid cancer incidence excess relative risk on postnatal dose. Excess relative risk was 0.66/Gy, р=0.006 with a five-year latency period. While estimating excess relative risk in different age groups at the beginning of exposure, a significant risk was present only in the age group under 1 year and amounted to 2.16/Gy; р<0.02 at the onset of exposure. The present results are in agreement with the results of the solid cancer incidence risk analysis both in the Techa River Cohort of exposed In-Utero where a statistically significant excess relative risk from a postnatal dose was revealed, and with the results of risk analysis in the Japanese cohort of people exposed in-utero and in early childhood.

The annual permissible atmospheric release levels of radionuclides are established with the condition that the population annual dose should not exceed the dose quota. Two conservative assumptions on the population exposure are applied in handbooks for calculation of the permissible release levels: a person can reside in any point outside the sanitary protection zone of nuclear facility; all exposure pathways, including food consumption, are determined by the place of residence. Calculation of the annual dose for adults living near the Smolensk, Rostov and Bilibino NPP was performed for three scenarios to evaluate the degree of conservatism of these assumptions. Scenario 1 assumed permanent residence in a critical point of the area with production of all food in this point and consumption only local food by the population. Scenario 2 assumed that a certain part of food is imported. In scenario 3 dose assessment was made for a permanent resident of the closest settlement near NPP, taking into consideration realistic characteristics of the exposure conditions. Atmospheric release levels of radionuclides assessed during the radiation and technical surveys of the NPP’s emission sources in 2017 – 2019 were used as the initial data. It is shown that the assumptions on the conditions of population exposure significantly affect the conservatism of the annual dose assessment. The calculated annual dose for the most conservative scenario is higher than for realistic scenario by 6,3 times (for the Smolensk NPP), 8,4 times (Rostov NPP), 883 times (Bilibino NPP). The highest degree of conservatism was shown for the internal radiation dose estimates. The results of calculation of the annual dose from NPP’s emissions strongly depend on the method for dose assessment from releases of ³H and ¹⁴C. Use of the regional values of consumption of locally produced food allows reasonable reducing the conservatism of the annual dose estimates from the NPP’s permanent radionuclide releases.

According to leading experts, the vast arsenal of radioprotective agents available in the world today does not fully meet modern practical needs, both in the field of radiation protection, and in the prevention and treatment of complications of radiotherapy. The purpose of the study was to evaluate the effect of the salt-forming acids type on the radioprotective activity of NOS inhibitor T1023. The chemical part of this study included methods of chemical synthesis, physicochemical and elemental analysis. Pharmacological part – assessment of acute toxicity using V.B. Prozorovsky express method and the study of radioprotective activity using Till and McCulloch method based on the ability of mice hematopoietic cells to form spleen colonies after irradiation. The number of endogenous hematopoietic spleen colonies were assessed on the 8th day after total exposure to gamma-irradiation at a dose of 6 Gy in six independent experiments. As a result of directed chemical synthesis, six new derivatives of T1023 – salts of N-isobutanoyl-S-isopropylisothiourea have been developed, identified and characterized. The results of studying the safety and radioprotective activity of the synthesized compounds showed that changes in the salt-forming acid don’t significantly influence the toxicity: all studied compounds are in the 3rd class of toxicity and hazard. At the same time, it was found that the replacement of the salt-forming acid significantly influenced the severity of the radioprotective effect. For some of these compounds radioprotective efficacy is comparable to or exceeds the efficacy of the initial compound T1023. It is important to note that these new compounds were used in lower, more save doses than T1023. The results suggest promising further development of NOS inhibitors – isothiourea derivatives as radioprotective agents.

The paper presents the data that allow calculate the attenuation factors in lead, tungsten and concrete of various thicknesses or the thickness of shielding made of these materials for a given attenuation factor for the spectra of gamma radiation of ¹³¹I and ¹⁷⁷Lu radionuclides. Using these data the effectiveness of the protection of supporting equipment (portable containers, shielded syringes, etc.) and the possible doses of external radiation of medical personnel in the radionuclide therapy department were calculated. It is shown that there are short-term operations in the production process when a radiation source (container with a capsule with activity, syringe with activity), being near the body of a medical worker, creates a significant dose rate. For this reason the annual individual dose of external exposure of a medical worker can approach or exceed 1/3 of the dose limit. Calculation of the attenuation of ¹³¹I gamma radiation by stationary shield showed that the thickness of walls and floors made of concrete 200 – 400 mm will ensure that the permissible values of the dose rates of gamma radiation in the air do not exceed at annual turnover of activity in the radionuclide therapy department of ~ 3.3 · 10¹² Bq.

The article provides a radiation-hygienic assessment of the current state of drinking water supply sources for the population in the observation area of the the Beloyarsk NPP and the Institute of Nuclear Materials. We determined the content of natural (²³⁴U, ²³⁸U, ²²⁶Ra, ²²⁸Ra, ²¹⁰Po, ²²²Rn, ²¹⁰Pb, ²²⁸Th, ²³⁰Th, ²³²Th) and technogenic (³H, ¹⁴C, ⁶⁰Co, ⁹⁰Sr, ¹³⁴Cs, ¹³⁷Cs, ²³⁸Pu, ^239,240Pu, ²⁴¹Am) radionuclides in drinking water of tap water, water boreholes and water wells in test settlements located at different distances and directions from radiation hazardous facilities. Results of monitoring of water sources in 2012–2013 and 2019 showed the radiation safety of drinking water in the vicinity of the Beloyarsk NPP according to several criteria. Thus, the maximum levels of the gross specific alpha-activity of radionuclides in water samples were 3.9 times lower than the control level (0.2 Bq/kg), the gross specific beta-activity was 5.7 times lower than the control level (1 Bq/ kg). Over the entire observation period, none of the drinking water samples exceeded the control levels both for individual radionuclides and for the sum of the ratios of specific activities to control levels. The content of natural and artificial radionuclides in drinking water near the Beloyarsk NPP decreases in the following order: water wells > water boreholes > tap water. For the past 20 years, there was a decrease in tritium specific activity in drinking water of the Beloyarsk NPP region by 20–35%, depending on the source of water supply. It was noted that the launch of the BN-800 reactor also did not lead to an increase in the content of other artificial radionuclides (⁹⁰Sr, ¹³⁷Cs) in groundwater. The average annual effective dose of internal exposure of the population due to drinking water consumption in the vicinity of the Beloyarsk NPP is 0.05 mSv, according to conservative estimates – 0.07 mSv, which is below the radiation safety threshold (0.1 mSv/a) recommended by the WHO. Natural radionuclides play the primary role in the formation of the annual average effective dose for internal irradiation (98.9%) due to drinking water consumption on the considered territories. ²¹⁰Po makes the largest contribution to the dose from natural radioisotopes – 43%, somewhat less is made by ²¹⁰Pb – 25%. The third place in the dose formation from natural radionuclides belongs to ²³⁴U (8%), ²²⁸Ra (7%), ²²⁶Ra (6%) and ²³⁰Th (6%). The contribution of other natural radioisotopes in the formation of the internal radiation dose from drinking water consumption does not exceed 2-3%. The contribution of technogenic radionuclides to the annual average effective dose from the consumption of drinking water is negligible (about 1%). Of the technogenic components, ⁹⁰Sr (60%), ³H (20%), and ²⁴¹Am (12%) play the most significant role in the formation of the internal exposure dose.

Objectives. To define the levels of volume activity of tritium compounds and fraction of organically bound tritium in urine of chemical production workers of “Mayak Production Association” in present-day conditions; to identify the relationship between volume activity levels and professional occupation (department and profession). Material and methods. 245 urine samples from 171 workers of Mayak Production Association tritium production facility were collected in the period from 2017 to 2019. Volume activity of tritium compounds was measured by liquid scintillation method using spectrometer Quantulus-1220. The samples were distilled or dried and then combusted using an automatic preparation and oxidization system Sample Oxidizer A307. The “R” software was used for statistical analysis and for processing the measurement results and occupational factors. Chaddok’s scale was applied to determine the degree of correlation. The significance level was taken equal to 5%. Results. The value of total tritium volume activity in the urine and tritium volume activity in the water phase varied within 4 orders of magnitude (from ~30 Bq/dm³ to ~250 kBq/dm³). The value of volume activity of organically bound tritium in the urine varied within 2 orders of magnitude (from ~6 Bq/dm³ to ~3000 kBq/dm³). The fraction of organically bound tritium in the urine of the workers was within the range from 0,07% to 74%, and did not differ statistically significantly from lognormal distribution with parameters GM=2,7% and GSD=3,7. Very high rank correlation was detected between total volume activity of tritium compounds and tritium volume activity in the water phase in the urine. Noticeable rank correlations were detected between the total volume activity of tritium compounds in the urine and volume activity of organically bound tritium, as well as between tritium volume activity in the water phase and volume activity of organically bound tritium in the urine. The total tritium volume activity and tritium volume activity in the water phase in the urine of the workers of the 1st department and of the analytical laboratory of Mayak Production Association tritium production facility were statistically significantly higher than in the workers of the 2nd department according to median values. Statistically significant differences between medians of the total tritium volume activity in the urine and tritium volume activity in the water phase related to profession were observed only in the workers in the 1st department. Conclusion. Estimation of tritium volume activity in the water phase by the level of total tritium volume activity in the urine without sample preparation is possible with 95% reliability within limits of one order of magnitude towards the model value. Estimation of volume activity of organically bound tritium in the urine without sample preparation by the level of total tritium volume activity in the urine without sample preparation is possible with 95% reliability within limits of two orders of magnitude towards the model value. The effect of occupational factors to the levels of volume activity of tritium compounds in the urine of Mayak Production Association professional workers was detected.

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.

The paper presents results of the radon survey carried out in preschool and school institutions in Dushanbe, Republic of Tajikistan. Radon concentration was measured using solid state nuclear track detectors Radtrak². Track detectors were exposed for 3 months during the heating and warm seasons of the year in the same premises. In total, the measurements were performed in 200 premises of 14 kindergartens and 36 schools. The radon equilibrium equivalent concentration during the heating and warm seasons and the annual average radon equilibrium equivalent concentration were calculated. Annual average radon equilibrium equivalent concentration in surveyed buildings ranged from 42 to 331 Bq/m³ with the mean value of 98 Bq/m³ on the first floor and 56 Bq/m³ on the second floor. It was shown that both seasonal values and annual average value of radon equilibrium equivalent concentration in the premises on the second floor are lower than in the premises on the first floor. The annual average effective dose to children from exposure to radon and its progeny in the premises of schools and kindergartens in Dushanbe ranged from 0,64 to 1,64 mSv. The limit value of annual average radon equilibrium equivalent concentration in dwellings and public buildings is set to 100 Bq/m3 for newly built buildings and 200 Bq/m³ for existing buildings in the Radiation safety norms (NRB-06) of the Republic of Tajikistan. This limit was exceeded only on the first floors in one kindergarten during the heating season, in three schools during the warm season and in eight schools during the heating season. When comparing the results of measurements of radon equilibrium equivalent concentration with data on the geological structure of underlying rocks at the locations of the surveyed buildings, no regularity was found. Additional detailed measurements in the buildings, including basements, will help to identify the source of radon entry into the indoor air and to develop recommendations for implementing radon remediation actions separately for each building. The survey results were also used to develop a radon map of Dushanbe.