The aim of this study was to evaluate the activity of 225 Ac in urine of patients undergoing radionuclide therapy with 225 Ac-DOTA-TATE. Activity concentration was determined in the urine samples collected within 72 hours after injection of 225 Ac-DOTA-TATE, using the ORTEC semiconductor gamma spectrometer, model TSP-DX-100T-PAC-PKG-1. Calculation of excreted activities was additionally performed based on scintig- raphy scans of patients receiving 225 Ac-DOTA-TATE. Scans were conducted 5 times for each patient: immedi- ately after injection, at 4 hours, and on the 1st, 2nd, and 3rd days after injection of the radiopharmaceutical. Absolute activity values and fractions of the injected activity were calculated based on the specific activity values. The results of the calculated activity concentration values demonstrate that maximum excretion was observed within the four hours after 225 Ac-DOTA-TATE injection. Significant differences between the two methods of determining 225 Ac activity were observed only on the third day after radiopharmaceutical injection, which allows for the simplification of future experimental work by using indirect radioactivity measurement methods for activity calculations. There were no significant differences between patient groups with different number of 225 Ac-DOTA-TATE injection, which allows for the exclusion of this parameter in the evaluation of experimental results. The results of this study represent the first published experimental data on the determi- nation of actinium excretion in patients.

INTRODUCTION: Peptide receptor therapy based on the 225 Ac radionuclide, due to the targeted effect on tumor cells, is the most promising method of treatment for patients with generalized forms of neuroendocrine tumors and castration-resistant prostate cancer. OBJECTIVE: The aim of the work was to evaluate the effectiveness of radioligand therapy of medicinal radiopharmaceuticals with 225 Ac. MATERIALS AND METHODS: Radioligand therapy based on 225 Ac radionuclide was performed in 7 patients with generalized prostate cancer and 3 patients with neuroendocrine tumors. RESULTS: Systemic radiation therapy with 225 Ac-PSMA 617 and 225 Ac-DOTATE showed its effectiveness in clinical practice — patients have a decrease in the level of accumulation of the radiopharmaceutical (RP) in pathological foci on PET-CT with 68 Ga-PSMA and 68 Ga-DOTATE; a decrease in the level of prostate-specific antigen (PSA) in the blood (for prostate cancer); reduction of manifestations of asthenic, pain and carcinoid (for neuroendocrine tumors) syndromes. Dosimetric studies make it possible to assess the biodistribution of a radiopharmaceutical drug in the body, accumulation in target organs and lesions. CONCLUSION: The appointment of this type of treatment requires an integrated approach based on a thorough study of medical records, assessment of the receptor status of the tumor tissue, timely detection and prediction of adverse reactions.

This study presents results of radiation-hygienic surveys of the Bryansk Oblast settlements bordering the Republic of Belarus. The data were obtained in the course of implementation of measures of the “Program of joint activities of Russia and Belarus within the framework of the Union State for the protection of the population and rehabilitation of the territories affected by the Chernobyl NPP accident” in 2019–2022. The first part of the study presents a general characteristic of the current state of the problem of returning the residents of radioactively contaminated territories to normal living conditions and provides information on the settlements of the surveyed region. The modern demographic composition of the population is considered; the structure of private subsidiary plots is investigated. The results described in this part of the study indicate the main ways, which are relevant for the formation of the internal exposure dose of the public at the current stage of the radiation accident.

During a stay in a radioactively contaminated forest, a person is inevitably exposed to ionizing radiation from the man-made radionuclides. The purpose of this study was to evaluate the external component of the annual effective dose due to exposure in the forests contaminated following the Chernobyl accident. The study was conducted in the south-western districts of the Bryansk region of Russia in the period 2015–2021. Field (in situ) gamma spectrometric measurements were carried out on 46 forest plots located in the areas of 27 settlements. As of 01.01.2017, the officially established values of soil contamination density with 137Cs in the territory of the settlements themselves were in the range from 33 to 2050 kBq/m2 . According to the field gamma spectrometry, the density of soil contamination with 137Cs on the forest plots varied from 21 to 1930 kBq/m2 . The density of soil contamination with 137Cs in forest was in good agreement with the officially established level of soil contamination with 137Cs in the nearby settlement: the ratio of one indicator to another ranged from 0.70 to 1.32 (mean = 0.94; median = 0.95). The scatter in the measured values of the ambient dose equivalent rate from 137Cs was quite significant: more than one order of magnitude, from 31 to 2700 nSv/h. The variability of the ambient dose equivalent rate from natural radionuclides was relatively small: from 13 to 29 nSv/h. Based on the obtained experimental data and on published values of the duration of human stay in forest, the annual effective dose to selected groups of population was estimated. The dose from natural radionuclides, even in the case of a prolonged stay in the forest (1400 hours per year for foresters), did not exceed 0.02 mSv/year. The estimated values of the effective dose from 137Cs varied very widely from 0.001 to 1.9 mSv/year, depending on the selected forest plot and population group. On the whole, the data obtained indicate that the officially established values of the density of soil contamination with 137Cs in a settlement can be directly used in dosimetric models to estimate the component of the effective dose to a person due to his/her staying in the forest which is located in the area of this settlement. The currently recommended conversion coefficient from the density of soil contamination with 137Cs in a settlement to the ambient dose equivalent rate from 137Cs in the nearby forest is 1.28 (nSv/h)/(kBq/m2 ). To estimate the effective dose from natural radionuclides, it is recommended to use the value of the ambient dose equivalent rate equal to 21 nSv/h.

The paper presents the activities of Rospotrebnadzor to ensure radiation safety in the framework of nuclear and radiation terrorism counteractions during the FIFA World Cup 2018 in Russia. One of the main activities of Rospotrebnadzor was to ensure radiation safety of food and drinking water. This task was solved by placing stationary radiation monitoring systems and organizing of continuous radiation monitoring of all foodstuffs and drinking water incoming to all sports facilities. In addition, selective radiation monitoring of samples of cooked food and drinking water at the catering facilities of the stadiums was organized. The second important activity was to ensure the radiation safety at the sites of mass people crowding with the use of portable equipment and/or car-borne radiological laboratories. The third activity was the identification and examination of the identified sources of ionizing radiation in case of alarm of radiation monitoring systems. The last but not the least activity was the interdepartmental cooperation, the effectiveness of which directly affects the response and resolution of issues related to emergency situations or situations that threaten radiation safety. The paper also briefly described the activities of the Saint-Petersburg Research Institute of Radiation Hygiene after Professor P.V. Ramzaev in the framework of ensuring radiation safety at the FIFA World Cup 2018.

Samples of vegetation (vascular plants) were collected at 14 grasslands on Kunashir, Iturup, Urup and Paramushir Islands in August–September 2012. All surveyed grasslands were virgin lands with respect to Fukushima fallout. Four plots were used as pastures for cattle in 2012. About 1 kg of green vegetation (mixed grass-forb crop) was taken from each of 13 plots. Seven samples of wormwood (Artemisia sp.) and three samples of Kuril dwarf bamboo (Sasa sp.) of the same mass were collected for comparison. A density of the above ground biomass was estimated at one of the plots. Activities of 134Cs and 137Cs radionuclides were determined by direct γ-ray spectrometry method using HP-germanium detectors. Inventories of 134Cs and 137Cs in the top 20 cm layer of soil were estimated by the authors earlier for each of these 14 plots based of the soil samples analysis. Caesium-134, a marker of Fukushima fallout, was determined in 18 of 24 vegetation samples. Caesium-137 activity was quantified in all of 24 samples. The activity concentration of the radionuclides in plants (wet weight) ranged from <0.05 Bq kg−1 to 1.6 Bq kg-1 for 134Cs and from 0.06 Bq kg−1 to 5.8 Bq kg-1 for 137Cs. About 2/5 (median = 41%, n = 18) of the total activity of 137Cs in plants was associated with the Fukushima accident. The soil-to-plant aggregated transfer coefficient (Tag) values in mixed grass-forb crop ranged from <0.2 × 10–3 m2 kg-1 to 11 × 10–3 m2 kg-1 for 134Cs and from 0.08 × 10–3 m2 kg-1 to 3.3 × 10–3 m2 kg-1 for 137Cs. The Tag values for 134Cs were statistically significantly higher compared to the Tag values for 137Cs. The median Tag for 134Cs in mixed grass-forb crop decreased in the 2011–2012 period by a factor of about two: from 12 × 10–3 m2 kg-1 to 6.6 × 10–3 m2 kg-1. The ecological half-time, Teco, of 134Cs in the plants was approximately one year. In 2011–2012, the median Tag for pre-Fukushima 137Cs in mixed grass-forb crop was estimated as 0.12 × 10–3 m2 kg-1. This value is lower by a factor of 100 and 50 compared to the median values of Tag that were deduced for Fukushima-derived radiocaesium in 2011 and 2012, respectively. The radiocaesium Tag values for Sasa sp. and Artemisia sp. agreed with those for mixed grass-forb crop. At grasslands with the aboveground biomass density of 1 kg m–2 and the Tag of 6 × 10–3 m2 kg-1 for 134Cs, the contribution of the vegetation contamination to total inventory of the radionuclide did not exceed 1%. For 137Cs, this contribution was less than 0.1%.

The study was conducted on Kunashir, Shikotan and Iturup Islands (Sakhalin Region of Russia) in order to evaluate the impact of the Fukushima accident on the “soil–grass–cow’s milk” exposure pathway. A total of 22 samples of cow’s milk were collected in the May 2011 – September 2012 period. Radiocaesium was isolated from thermally treated specimens using the antimony–iodide radiochemical method. The activity concentrations of 134Cs and 137Cs were measured by γ-ray spectrometry using high purity germanium detectors. Caesium-134 was detected in 18 of the total 22 samples of milk. The activity concentration of 134Cs in the samples varied from 0.08 Bq kg–1 to 2.00 Bq kg–1. Caesium-137 was quantified in all 22 samples: range = 0.088–2.43 Bq kg–1. On average, more than a half of the total 137Cs in the milk samples from Sakhalin Region was of Fukushima origin (mean = 60%, median = 57%, range = 13–95%). The highest activity concentrations and values of the soil–to–milk aggregated transfer coefficient, Tag, for 134Cs (and Fukushimaderived 137Cs) were observed in milk samples collected in mid-May 2011. The mean Tag values decreased in the May–October period of 2011 from 12 × 10−3 m2 kg–1 to 2.3 × 10−3 m2 kg–1. In September 2012, the Tag values remained unchanged (mean = 2.8 × 10−3 m2 kg–1) compared to those in September–October 2011. In the autumns of 2011 and 2012, the calculated values of Tag for Fukushima-derived radiocaesium were on average 17 times larger than the ones for pre-Fukushima 137Cs. The higher transfer of Fukushima-derived 137Cs (compared to pre-Fukushima 137Cs) for milk reflected the difference between the “new” and “aged” radiocaesium in the intensity of the radionuclide transfer from soil to grassland plants which were the major component of the cow’s diet in the area of our study. The ratio between the 137Cs activity concentration in the milk (fresh weight) and that in the grassland plants (dry weight) ranged from 0.028 to 0.11. The effective dose from ingestion of Fukushima-derived radiocaesium in locally produced cow’s milk for critical group of adult residents of the southern Kuril in the first year after the accident is conservatively estimated as 0.0027 mSv. The Fukushima accident has had a negligible impact on radiocaesium contamination of cow’s milk and the corresponding human exposure on the southern Kuril Islands: Shikotan, Kunashir and Iturup.

The study was conducted on Kunashir, Shikotan and Iturup Islands (Sakhalin Region of Russia) in order to evaluate the impact of the Fukushima accident on the “soil–grass–cow’s milk” exposure pathway. A total of 22 samples of cow’s milk were collected in the May 2011 – September 2012 period. Radiocaesium was isolated from thermally treated specimens using the antimony–iodide radiochemical method. The activity concentrations of 134Cs and 137Cs were measured by γ-ray spectrometry using high purity germanium detectors. Caesium-134 was detected in 18 of the total 22 samples of milk. The activity concentration of 134Cs in the samples varied from 0.08 Bq kg–1 to 2.00 Bq kg–1. Caesium-137 was quantified in all 22 samples: range = 0.088–2.43 Bq kg–1. On average, more than a half of the total 137Cs in the milk samples from Sakhalin Region was of Fukushima origin (mean = 60%, median = 57%, range = 13–95%). The highest activity concentrations and values of the soil–to–milk aggregated transfer coefficient, Tag, for 134Cs (and Fukushimaderived 137Cs) were observed in milk samples collected in mid-May 2011. The mean Tag values decreased in the May–October period of 2011 from 12 × 10−3 m2 kg–1 to 2.3 × 10−3 m2 kg–1. In September 2012, the Tag values remained unchanged (mean = 2.8 × 10−3 m2 kg–1) compared to those in September–October 2011. In the autumns of 2011 and 2012, the calculated values of Tag for Fukushima-derived radiocaesium were on average 17 times larger than the ones for pre-Fukushima 137Cs. The higher transfer of Fukushima-derived 137Cs (compared to pre-Fukushima 137Cs) for milk reflected the difference between the “new” and “aged” radiocaesium in the intensity of the radionuclide transfer from soil to grassland plants which were the major component of the cow’s diet in the area of our study. The ratio between the 137Cs activity concentration in the milk (fresh weight) and that in the grassland plants (dry weight) ranged from 0.028 to 0.11. The effective dose from ingestion of Fukushima-derived radiocaesium in locally produced cow’s milk for critical group of adult residents of the southern Kuril in the first year after the accident is conservatively estimated as 0.0027 mSv. The Fukushima accident has had a negligible impact on radiocaesium contamination of cow’s milk and the corresponding human exposure on the southern Kuril Islands: Shikotan, Kunashir and Iturup .

The caesium-134 and caesium-137 radionuclides released into the atmosphere as a result of the Fukushima accident were dispersed over the entire Northern Hemisphere. To assess the risks associated with the exposure due to Fukushima fallout, a comprehensive radiological survey was performed in the Russian Far East. One of the objectives of the project was to determine the densities of ground contamination by 137Cs and 134Cs on Sakhalin and Kuril Islands that constitute the Sakhalin oblast, an administrative region of Russia. In 2011, soil samples were collected at grasslands on Sakhalin, Kunashir and Shikotan Islands and results of the 2011 survey were published earlier. In the present study, activities of 137Cs and 134Cs were measured in soil samples obtained on Kunashir, Iturup, Urup and Paramushir Islands in 2012. From the studies carried out in 2011–2012, it was estimated that the Fukushima-derived 134Cs inventory at 37 undisturbed grassland sites in the Sakhalin oblast varied from 8 Bq m−2 to 345 Bq m−2 (as of 15 March 2011). For this date, the inventory of the 137Cs radionuclide originated from the Fukushima NPP was assumed to be the same as that of the 134Cs radionuclide. The southern Kuril Islands were the most contaminated due to Fukushima fallout. In 2011 and 2012, Fukushima-derived radiocaesium was detected only in the top 5 cm layer of soil at all sites, excluding one, where ~20% of the 134Cs inventory was found at a depth of 5–10 cm. In the period September 2011– September 2012, the inventory of 134Cs declined by ~26% at four plots selected for long-term observations. The decline in the 134Cs inventory closely corresponded to the reduction (29%) of 134Cs activity due to radioactive decay. Pre-accidental inventory of 137Cs in the top 20 cm layer of soil ranged from 53 Bq m−2 to 3630 Bq m−2. The mean reference inventory of pre-accidental 137Cs for 13 representative sites was amounted as 2600 Bq m−2. Hence, the Fukushima accident added relatively small quantities of radioactivity to the reference preaccidental inventory of 137Cs in grassland soils in the Sakhalin region: about 3% (~80 Bq m−2) on the average and 15% (~350 Bq m−2) at the maximum. Such small additional radioactive contamination is absolutely safe from a radiological point of view.

The Chernobyl accident in 1986 is one of the most large-scale radiation accidents in the world. It led to radioactive contamination of large areas in the European part of the Russian Federation and at the neighboring countries. Now, there are more than 4000 settlements with the total population of 1.5 million in the radioactively contaminated areas of the Russian Federation. The Bryansk region is the most intensely contaminated region. For example, the Krasnogorskiy district still has settlements with the level of soil contamination by cesium-137 exceeding 40 Ci/km 2 . The regions of Tula, Kaluga and Orel are also significantly affected. In addition to these four regions, there are ten more regions with the radioactively contaminated settlements. After the Chernobyl accident, the affected areas were divided into zones of radioactive contamination. The attribution of the settlements to a particular zone is determined by the level of soil contamination with 137 Cs and by a value of the average annual effective dose that could be formed in the absence of: 1) active measures for radiation protection, and 2) self-limitation in consumption of the local food products. The main regulatory document on this issue is the Federal law № 1244-1 (dated May, 15 1991) "On the social protection of the citizens who have been exposed to radiation as a result of the accident at the Chernobyl nuclear power plant". The law extends to the territories, where, since 1991: 1) the average annual effective dose for the population exceeds 1 mSv (the value of effective dose that could be formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products); 2) soil surface contamination with cesium-137 exceeds 1 Ci/km 2 . The paper presents results of calculations of the average effective doses in 2017. The purpose was to use the dose values (SGED 90 ) in zonation of contaminated territories. Therefore, the calculations have been done under the assumption that the doses were formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products. The dose to population, rather than the density of radioactive contamination of soil by 137 Cs, is the most objective characteristic of the actual radiation exposure to the residents of the contaminated areas.

The Chernobyl accident in 1986 being one of the most large-scale radiation accidents in the world led to radioactive contamination of large areas in the European part of the Russian Federation and at the neighboring countries. Nowadays, there are adout 4000 settlements with the total population of more than 1.5 million in the radioactively contaminated areas of the Russian Federation. The Bryansk region is the most intensely contaminated region: thus, in the Krasnogorskiy district, there are still settlements with the level of soil contamination with cesium-137 exceeding 40 Ci/km 2 . Tula, Kaluga and Orel regions are also significantly affected. In addition to these four regions, there are ten other regions with the settlements located in the zones of radioactive contamination. After the Chernobyl accident, the affected areas have been divided into the zones of radioactive contamination. Belonging of the settlements to the one or another zone is determined by level of soil contamination with 137Cs and by value of the average annual effective dose that could be formed in the conditions of the absence of active measures of radiation protection and self-limitation with respect of the consumption of the local food products. The paper presents results of calculations of the average accumulated effective doses for the population. It is known that the most objective qualitative and quantitative index of the estimation of the actual radiation influence on the population of contaminated territories is the accumulated dose to population. In contrast to average annual effective exposure dose, which is estimated based on certain assumptions, the value of average accumulated dose is based on the doses which were actually received by inhabitants.

The Chernobyl accident in 1986 is one of the most large-scale radiation accidents in the world. It led to radioactive contamination of large areas in the European part of the Russian Federation and at the neighboring countries. Now, there are more than 4000 settlements with the total population of 1.5 million in the radioactively contaminated areas of the Russian Federation. The Bryansk region is the most intensely contaminated region. For example, the Krasnogorskiy district still has settlements with the level of soil contamination by cesium-137 exceeding 40 Ci/km 2 . The regions of Tula, Kaluga and Orel are also significantly affected. In addition to these four regions, there are ten more regions with the radioactively contaminated settlements. After the Chernobyl accident, the affected areas were divided into zones of radioactive contamination. The attribution of the settlements to a particular zone is determined by the level of soil contamination with 137 Cs and by a value of the average annual effective dose that could be formed in the absence of: 1) active measures for radiation protection, and 2) self-limitation in consumption of the local food products. The main regulatory document on this issue is the Federal law № 1244-1 (dated May, 15 1991) “On the social protection of the citizens who have been exposed to radiation as a result of the accident at the Chernobyl nuclear power plant”. The law extends to the territories, where, since 1991: 1) the average annual effective dose for the population exceeds 1 mSv (the value of effective dose that could be formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products); 2) soil surface contamination with cesium-137 exceeds 1 Ci/km 2 . The paper presents results of calculations of the average effective doses in 2017. The purpose was to use the dose values (SGED 90 ) in zonation of contaminated territories. Therefore, the calculations have been done under the assumption that the doses were formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products. The dose to population, rather than the density of radioactive contamination of soil by 137 Cs, is the most objective characteristic of the actual radiation exposure to the residents of the contaminated areas.

The article contains substantiation of criteria of return of territories with radioactive pollution caused by Chernobyl NPP accident to conditions of normal population activity. It is established that in 12 entities of the Russian Federation (except Bryansk and Kaluga regions) all agricultural food produce, including that from the personal part-time farms, corresponds to hygienic specifications. Non- corresponding to the standard SanPiN 2.3.2.1078-01 on 137Cs are part of the milk samples produced at personal part-time farms of the Bryansk region and most of natural foodstuff samples (berries, mushrooms, fish and wild animals meat) in Bryansk and Kaluga regions. The content of 137Cs both in agricultural and in wild-growing foodstuff produced at radioactively contaminated territories depends not only on the density of radioactive pollution, but also on the types of soil. The average settlement annual effective dose of population irradiation (AAED90) in the 3700 among 4413 settlements as of 2014 was below 0.3 mSv/year. Only in 713 settlements of Bryansk, Kaluga, Oryol and Tula regions the AAED90 exceeds 0.3 mSv/year. In the Bryansk region, once subject to the greatest radioactive contamination, in 276 settlements AAED90 exceeds 1 mSv/year, and in 8 of them - 5 mSv/year.The legislation of the Russian Federation defines only criteria and requirements for consideration of the suffered territories as zones of radioactive contamination. Requirements on transfer of territories polluted by radiation accidents and their population to normal life activity conditions (regarding the radiological factor) are not developed.Radiological criteria are suggested for transfer of the settlements considered to be the zone of radioactive pollution to conditions of normal life activity: average irradiation dose of critical population group: 1.0 mSv per year and lower (AAED crit); decrease of radionuclide soil contamination density to the level enabling to use the territory for traditional agricultural production meeting sanitary requirements without special measures for decrease of the 137Cs or other radionuclides content.

The article contains substantiation of criteria of return of territories with radioactive pollution caused by Chernobyl NPP accident to conditions of normal population activity. It is established that in 12 entities of the Russian Federation (except Bryansk and Kaluga regions) all agricultural food produce, including that from the personal part-time farms, corresponds to hygienic specifications. Non- corresponding to the standard SanPiN 2.3.2.1078-01 on 137Cs are part of the milk samples produced at personal part-time farms of the Bryansk region and most of natural foodstuff samples (berries, mushrooms, fish and wild animals meat) in Bryansk and Kaluga regions. The content of 137Cs both in agricultural and in wild-growing foodstuff produced at radioactively contaminated territories depends not only on the density of radioactive pollution, but also on the types of soil. The average settlement annual effective dose of population irradiation (AAED90) in the 3700 among 4413 settlements as of 2014 was below 0.3 mSv/year. Only in 713 settlements of Bryansk, Kaluga, Oryol and Tula regions the AAED90 exceeds 0.3 mSv/year. In the Bryansk region, once subject to the greatest radioactive contamination, in 276 settlements AAED90 exceeds 1 mSv/year, and in 8 of them - 5 mSv/year. The legislation of the Russian Federation defines only criteria and requirements for consideration of the suffered territories as zones of radioactive contamination. Requirements on transfer of territories polluted by radiation accidents and their population to normal life activity conditions (regarding the radiological factor) are not developed. Radiological criteria are suggested for transfer of the settlements considered to be the zone of radioactive pollution to conditions of normal life activity: average irradiation dose of critical population group: 1.0 mSv per year and lower (AAED crit); decrease of radionuclide soil contamination density to the level enabling to use the territory for traditional agricultural production meeting sanitary requirements without special measures for decrease of the 137Cs or other radionuclides content.

The article contains the results of current internal exposure dose assessment for the citizens of some Bryansk region settlements affected by radioactive contamination due to the accident at Chernobyl NPP, obtained with the use of three different methodical approaches: based on the results of 137Cs content determination in the bodies of citizens of examined settlements; based on the data of radionuclide content in the local food products and structure of food ration of citizens; based on the data of groups and types of soil, prevailing in the farmland and in the forest areas. The comparison of resulting assessments is done.

Temporal variations of radionuclide levels in the epiphytic Usnea sp. lichens from the two islands Sakhalin and Kunashir, the Sakhalin region, Russia have been evaluated using the already published (2011–2013) and new experimental data (2015). A total of 62 lichen samples were measured using high purity germanium γ-ray detectors and multichannel analyzers. In the period 2011–2015, activity concentrations of the anthropogenic radionuclides 134Cs and 137Cs and the natural radionuclides 7Be and 40K were found to be in the range of (<0.53)–41.3, 0.55–50.6, 99–603 and 35–95 Bq kg–1 on dry weight, respectively. The activity concentrations of 134Cs and 137Cs in lichens were statistically significantly higher at Kunashir than at Sakhalin. The present-day levels of radiocesium activity concentrations in lichens are low: < 6 Bq kg–1 for 137Cs and <1 Bq kg–1 for 134Cs. A decline in the annual median 137Cs activity concentrations in lichens from 2011 to 2015 corresponds to a biological half-life of 1.2 y for Kunashir and 1.1 y for Sakhalin. The activity concentrations of 137Cs and 134Cs in lichens were strongly correlated (r=0.978, P<0.01) and the 134Cs biological half-life value of 1.2 y in the period 2011–2013 was similar to the corresponding 137Cs biological half-life value. The soil-tolichens aggregated transfer factor, Tag, for 134Cs at time t=0 after the Fukushima accident is calculated as 0.56 m2 kg–1 at Sakhalin and 0.31 m2 kg–1 at Kunashir. In contrast to radiocesium, the natural radionuclides 7Be and 40K did not show clear time-dependent variations in the Usnea lichens. No correlation was found between 7Be and 40K as well as between 40K and cesium radioisotopes. However, positive and statistically significant (P<0.05) correlations were obtained between 7Be and cesium radioisotopes. High abundance of the Usnea sp. lichens in the study area and large values of Tag for radiocesium in the lichens make these organisms suitable candidates for detection of low levels of airborne radioactive contamination of the environment.

The article discusses the issues associated with the current exposure of the population of 14 regions of Russia due to the Chernobyl accident, identified tasks facing Rospotrebnadzor today. The article describes criteria and requirements for ensuring of the mechanism of the transition of settlements from the conditions of a radiation accident to the public normal conditions.

The Chernobyl accident in 1986 is one of the most large-scale radiation accidents in the world. It led to radioactive contamination of large areas in the European part of the Russian Federation and at the neighboring countries. Now, there are more than 4000 settlements with the total population of 1.5 million in the radioactively contaminated areas of the Russian Federation. The Bryansk region is the most intensely contaminated region. For example, the Krasnogorskiy district still has settlements with the level of soil contamination by cesium-137 exceeding 40 Cu/km2. The regions of Tula, Kaluga and Orel are also significantly affected. In addition to these four regions, there are 10 more regions with the radioactively contaminated settlements. After the Chernobyl accident, the affected areas were divided into zones of radioactive contamination. The attribution of the settlements to a particular zone is determined by the level of soil contamination with 137Cs and by a value of the average annual effective dose that could be formed in the absence of: 1) active measures for radiation protection, and 2) self-limitation in consumption of the local food products. The main regulatory document on this issue is the Federal law № 1244-1 (dated May, 15,1991) «On the social protection of the citizens who have been exposed to radiation as a result of the accident at the Chernobyl nuclear power plant». The law extends to the territories, where, since 1991: – The average annual effective dose for the population exceeds 1 mSv (the value of effective dose that could be formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products); – Soil surface contamination with cesium-137 exceeds 1 Cu/km2. The paper presents results of calculations of the average effective doses in 2014. The purpose was to use the dose values (SGED90) in zonation of contaminated territories. Therefore, the calculations have been done under the assumption that the doses were formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products. The dose to population, rather than the density of radioactive contamination of soil by 137Cs, is the most objective characteristic of the actual radiation exposure to the residents of the contaminated areas.

The Chernobyl accident in 1986 is one of the most large-scale radiation accidents in the world. It led to radioactive contamination of large areas in the European part of the Russian Federation and at the neighboring countries. Now, there are more than 4000 settlements with the total population of 1.5 million in the radioactively contaminated areas of the Russian Federation. The Bryansk region is the most intensely contaminated region. For example, the Krasnogorskiy district still has settlements with the level of soil contamination by cesium-137 exceeding 40 Cu/km2. The regions of Tula, Kaluga and Orel are also significantly affected. In addition to these four regions, there are 10 more regions with the radioactively contaminated settlements. After the Chernobyl accident, the affected areas were divided into zones of radioactive contamination. The attribution of the settlements to a particular zone is determined by the level of soil contamination with 137Cs and by a value of the average annual effective dose that could be formed in the absence of: 1) active measures for radiation protection, and 2) self-limitation in consumption of the local food products. The main regulatory document on this issue is the Federal law № 1244-1 (dated May, 15,1991) «On the social protection of the citizens who have been exposed to radiation as a result of the accident at the Chernobyl nuclear power plant». The law extends to the territories, where, since 1991: – The average annual effective dose for the population exceeds 1 mSv (the value of effective dose that could be formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products); – Soil surface contamination with cesium-137 exceeds 1 Cu/km2. The paper presents results of calculations of the average effective doses in 2014. The purpose was to use the dose values (SGED90) in zonation of contaminated territories. Therefore, the calculations have been done under the assumption that the doses were formed in the absence of active radiation protection measures and self-limitation in consumption of the local food products. The dose to population, rather than the density of radioactive contamination of soil by 137Cs, is the most objective characteristic of the actual radiation exposure to the residents of the contaminated areas.