Minimal Internal Radiation Exposure in Residents Living South of the Fukushima Daiichi Nuclear Power Plant Disaster

Following the Fukushima nuclear power plant disaster, assessment of internal radiation exposure was indispensable to predict radiation-related health threats to residents of neighboring areas. Although many evaluations of internal radiation in residents living north and west of the crippled Fukushima nuclear power plant are available, there is little information on residents living in areas south of the plant, which were similarly affected by radio-contamination from the disaster. To assess the internal radio-contamination in residents living in affected areas to the south of the plant or who were evacuated into Iwaki city, a whole body counter (WBC) screening program of internal radio-contamination was performed on visitors to the Jyoban hospital in Iwaki city, which experienced less contamination than southern areas adjacent to the nuclear plant. The study included 9,206 volunteer subjects, of whom 6,446 were schoolchildren aged 4–15 years. Measurements began one year after the incident and were carried out over the course of two years. Early in the screening period only two schoolchildren showed Cs-137 levels that were over the detection limit (250 Bq/body), although their Cs-134 levels were below the detection limit (220 Bq/body). Among the 2,760 adults tested, 35 (1.3%) had detectable internal radio-contamination, but only for Cs-137 (range: 250 Bq/body to 859 Bq/body), and not Cs-134. Of these 35 subjects, nearly all (34/35) showed elevated Cs-137 levels only during the first year of the screening. With the exception of potassium 40, no other radionuclides were detected during the screening period. The maximum annual effective dose calculated from the detected Cs-137 levels was 0.029 and 0.028 mSv/year for the schoolchildren and adults, respectively, which is far below the 1 mSv/year limit set by the government of Japan. Although the data for radiation exposure during the most critical first year after the incident are unavailable due to a lack of systemic measurements, the present results suggest that internal radio-contamination levels more than one year after the incident were minimal for residents living south of the crippled Fukushima nuclear plant, and that the annual additional effective doses derived from internal Cs contamination were negligible. Thus, internal radio-contamination of residents living in southern radio-contaminated areas appears to be generally well controlled.     

An estimation of Canadian population exposure to cosmic rays

The worldwide average exposure to cosmic rays contributes to about 16% of the annual effective dose from natural radiation sources. At ground level, doses from cosmic ray exposure depend strongly on altitude, and weakly on geographical location and solar activity. With the analytical model PARMA developed by the Japan Atomic Energy Agency, annual effective doses due to cosmic ray exposure at ground level were calculated for more than 1,500 communities across Canada which cover more than 85% of the Canadian population. The annual effective doses from cosmic ray exposure in the year 2000 during solar maximum ranged from 0.27 to 0.72 mSv with the population-weighted national average of 0.30 mSv. For the year 2006 during solar minimum, the doses varied between 0.30 and 0.84 mSv, and the population-weighted national average was 0.33 mSv. Averaged over solar activity, the Canadian population-weighted average annual effective dose due to cosmic ray exposure at ground level is estimated to be 0.31 mSv.     

Limited Internal Radiation Exposure Associated with Resettlements to a Radiation-Contaminated Homeland after the Fukushima Daiichi Nuclear Disaster

Resettlement to their radiation-contaminated hometown could be an option for people displaced at the time of a nuclear disaster; however, little information is available on the safety implications of these resettlement programs. Kawauchi village, located 12–30 km southwest of the Fukushima Daiichi nuclear power plant, was one of the 11 municipalities where mandatory evacuation was ordered by the central government. This village was also the first municipality to organize the return of the villagers. To assess the validity of the Kawauchi villagers’ resettlement program, the levels of internal Cesium (Cs) exposures were comparatively measured in returnees, commuters, and non-returnees among the Kawauchi villagers using a whole body counter. Of 149 individuals, 5 villagers had traceable levels of Cs exposure; the median detected level was 333 Bq/body (range, 309–1050 Bq/kg), and 5.3 Bq/kg (range, 5.1–18.2 Bq/kg). Median annual effective doses of villagers with traceable Cs were 1.1 x 10^-2 mSv/y (range, 1.0 x 10^-2-4.1 x 10^-2 mSv/y). Although returnees had higher chances of consuming locally produced vegetables, Cochran-Mantel-Haenszel test showed that their level of internal radiation exposure was not significantly higher than that in the other 2 groups (p=0.643). The present findings in Kawauchi village imply that it is possible to maintain internal radiation exposure at very low levels even in a highly radiation-contaminated region at the time of a nuclear disaster. Moreover, the risks for internal radiation exposure could be limited with a strict food control intervention after resettlement to the radiation-contaminated village. It is crucial to establish an adequate number of radio-contaminated testing sites within the village, to provide immediate test result feedback to the villagers, and to provide education regarding the importance of re-testing in reducing the risk of high internal radiation exposure.     

Measurement of <Superscript>131</Superscript>I activity in thyroid of nuclear medical staff and internal dose assessment in a Polish nuclear medical hospital

This paper presents results of ¹³¹I thyroid activity measurements in 30 members of the nuclear medicine personnel of the Department of Endocrinology and Nuclear Medicine Holy Cross Cancer Centre in Kielce, Poland. A whole-body spectrometer equipped with two semiconductor gamma radiation detectors served as the basic research instrument. In ten out of 30 examined staff members, the determined ¹³¹I activity was found to be above the detection limit (DL = 5 Bq of ¹³¹I in the thyroid). The measured activities ranged from (5 ± 2) Bq to (217 ± 56) Bq. The highest activities in thyroids were detected for technical and cleaning personnel, whereas the lowest values were recorded for medical doctors. Having measured the activities, an attempt has been made to estimate the corresponding annual effective doses, which were found to range from 0.02 to 0.8 mSv. The highest annual equivalent doses have been found for thyroid, ranging from 0.4 to 15.4 mSv, detected for a cleaner and a technician, respectively. The maximum estimated effective dose corresponds to 32% of the annual background dose in Poland, and to circa 4% of the annual limit for the effective dose due to occupational exposure of 20 mSv per year, which is in compliance with the value recommended by the International Commission on Radiological Protection.     

External and internal irradiation of a Rural Bryansk (Russia) population from 1990 to 2000, following high deposition of radioactive caesium from the chernobyl accident

In 1990, a joint Nordic-Russian project was initiated in order to make independent estimations of the effective dose to selected groups of inhabitants in a highly contaminated area around the city of Novozybkov in the western Bryansk region of Russia. The inhabitants were living in six villages with initial contamination levels of ¹³⁷Cs between 0.9 and 2.7 MBq m⁻². Some villages had been decontaminated, others not. Both school children and adults participated in the study. The external irradiation of 100–130 inhabitants was determined during 1 month in September-October each year from 1990 to 2000 (except 1999), using individual thermoluminescent dosemeters. The body burden of ^137,134Cs was determined by in vivo measurements in about 500 inhabitants annually from 1991 to 2000, and for a subgroup also with analysis of the ¹³⁷Cs concentration in urine. The mean effective dose (E) from external and internal irradiation due to ^137,134Cs deposition varied between 2.5 and 1.2 mSv per year between 1990 and 2000. The total mean E decreased, on average, by 9% per year, while the mean external dose decreased by 16% per year. The dose rate from internal radiation decreased more slowly than the dose rate from external radiation, and also showed an irregular time variation. The contribution from the internal dose to the total E was 30–50%, depending on the village. Predictions for the long-term changes in the effective dose to people living in the areas are presented. The cumulated E for the 70 years following the accident was estimated to be about 90 mSv with the assumption that both internal and external dose decrease by 2% per year after year 2000. The highest E during a life-time received by single individuals living in the area may amount to around 500 mSv considering the individual variations in E.     

Studies of radon-exposed miner cohorts using a biologically based model: comparison of current Czech and French data with historic data from China and Colorado

Cosmic radiation is an occupational risk factor for commercial aircrews. In this large European cohort study (ESCAPE) its association with cancer mortality was investigated on the basis of individual effective dose estimates for 19,184 male pilots. Mean annual doses were in the range of 2–5 mSv and cumulative lifetime doses did not exceed 80 mSv. All-cause and all-cancer mortality was low for all exposure categories. A significant negative risk trend for all-cause mortality was seen with increasing dose. Neither external and internal comparisons nor nested case-control analyses showed any substantially increased risks for cancer mortality due to ionizing radiation. However, the number of deaths for specific types of cancer was low and the confidence intervals of the risk estimates were rather wide. Difficulties in interpreting mortality risk estimates for time-dependent exposures are discussed.Abbreviations CI confidence interval - CLL chronic lymphatic leukemia - RRC radiation-related cancers - NRRC non-radiation-related cancers - RR relative risk - SMR standardized mortality ratio     

Long-term external radiation exposure of inhabitants in the western Bryansk region of Russia as a consequence of the Chernobyl accident

The western Bryansk region in south-western Russia was highly contaminated with ¹³⁷Cs and ¹³⁴Cs due to the Chernobyl accident in 1986. In 1990, a joint Nordic-Russian project was initiated in order to make measurements and estimates of the absorbed doses to selected groups of inhabitants in this area. The participating individuals were living in small villages with contamination levels between 0.9 and 2.7 MBq m^–2. Only some villages had been decontaminated. Both schoolchildren and adults participated in the study and the number of persons was between 100 and 130 each year, residing in 5 villages. Every year in September–October, from 1990 to 1998, we performed individual measurements of external absorbed doses, assessed with thermoluminescent (TL) dosemeters (LiF). The mean effective dose per year from external irradiation due to the Chernobyl accident of the inhabitants in the villages ranged between 0.8 and 2.9 mSv during the study period and decreased with an apparent half-time of 3.7–8.2 years, depending on village and group. The highest individual doses within one village were, on average higher by a factor of 3 than the mean value for that village. Under the conservative assumption of a decrease rate in the external effective dose of 2% per year after 1998, individuals in the most highly exposed village are assumed to receive a life-time effective dose of about 75 mSv (between 1986 and 2056) from external exposure to caesium radionuclides. The mean value for the villages under study was estimated to be around 65 mSv using the assumed rate of decrease. Received: 20 December 2000 / Accepted: 1 October 2001     

Esophagus cancer and radiation exposure due to nuclear test fallout: an analysis based on the data of the Semipalatinsk historical cohort, 1960-1999

This paper describes the Semipalatinsk historical cohort study and, in particular, examines the association between combined external and internal radiation exposure and esophagus cancer. Esophagus cancer is the most frequent single cancer site in the cause of death follow-up for the Semipalatinsk cohort. Set up in the 1960s, this historical cohort included 10 exposed settlements in the vicinity of the Semipalatinsk nuclear test site in East Kazakhstan as well as 6 comparison settlements in a low exposure area of the same region. The external and internal radiation doses to the population of the settlements under study were mainly due to local fallout from atmospheric nuclear testing (1949-1962). The database includes dosimetry and health information for 19.545 inhabitants of exposed and comparison villages in the Semipalatinsk region, comprising a total of 582.750 person-years of follow-up between 1960 and 1999. Cumulative effective dose estimates in this cohort range from 20 mSv to -4 Sv, with a mean dose of 634 mSv in the exposed group. Relative risks were calculated in terms of rate ratios, using a Poisson regression model for grouped person-time data. Esophagus cancer was found substantially elevated, with a statistically significant increase of the relative risk with dose and an ERR/Sv of 2.37 (1.45; 3.28) for the total cohort. If the data set was restricted to the exposed group only, the ERR/Sv was found considerably lower (0.18 (-0.16; 0.52)), whereas the dose-response remained significant only in women. Overall, our results based on the Semipalatinsk historical cohort indicate an association between fallout exposure and the risk of esophagus cancer that should be further investigated.     

Trends in childhood leukaemia in the Nordic countries in relation to fallout from atmospheric nuclear weapons testing.

OBJECTIVE--To obtain further information about the risks of childhood leukaemia after exposure to ionising radiation at low doses and low dose rates before or after birth or to the father''s testes shortly before conception. DESIGN--Observational study of trends in incidence of childhood leukaemia in relation to estimated radiation exposures due to fallout from atmospheric nuclear weapons testing during the 1950s and 1960s. SETTING--Nordic countries. SUBJECTS--Children aged under 15 years. MAIN OUTCOME MEASURES--Incidence rates of leukaemia by age at diagnosis, sex, country, and calendar year of diagnosis or year of birth; exposure category; relation between leukaemia and exposure for children aged 0-14 and 0-4 separately. RESULTS--During the high fallout period the average estimated dose equivalent to the fetal red bone marrow was around 140 mu Sv and the average annual testicular dose 140 mu Sv. There was little evidence of increased incidence of leukaemia among children born in these years. Doses to the red bone marrow of a child after birth were higher, and during the high exposure period children would have been subjected to an additional dose equivalent of around 1500 mu Sv, similar to doses received by children in several parts of central and eastern Europe owing to the Chernobyl accident and about 50% greater than the annual dose equivalent to the red bone marrow of a child from natural radiation. leukaemia incidence and red marrow dose was not related overall, but rates of leukaemia in the high exposure period were slightly higher than in the surrounding medium exposure period (relative risk for ages 0-14: 1.07, 95% confidence interval 1.00 to 1.14; for ages 0-4: 1.11, 1.00 to 1.24). CONCLUSIONS--Current predicted risks of childhood leukaemia after exposure to radiation are not greatly underestimated for low dose rate exposures.     

Measurement of <Superscript>131</Superscript>I activity in air indoor Polish nuclear medical hospital as a tool for an internal dose assessment

This paper presents results of ¹³¹I air activity measurements performed within nuclear medical hospitals as a tool for internal dose assessment. The study was conducted at a place of preparation and administration of ¹³¹I (“hot room”) and at a nurse station. ¹³¹I activity measurements were performed for 5 and 4 consecutive working days, at the “hot room” and nurse station, respectively. Iodine from the air was collected by a mobile HVS-30 aerosol sampler combined with a gas sampler. Both the gaseous and aerosol fractions were measurement. The activities in the gaseous fraction ranged from (28?±?1 Bq m^?3) to (492?±?4) Bq m^?3. At both sampling sites, the activity of the gaseous iodine fraction trapped on activated charcoal was significantly higher than that of the aerosol fraction captured on Petrianov filter cloth. Based on these results, an attempt has been made to estimate annual inhalation effective doses, which were found to range from 0.47 mSv (nurse female) to 1.3 mSv (technician male). The highest annual inhalation equivalent doses have been found for thyroid as 32, 27, 13, and 11 mSv, respectively, for technician male, technical female, nurse male, and nurse female. The method presented here allows to fill the gaps in internal doses measurements. Moreover, because method has been successful used for many years in radioactive contamination monitoring of air in cases of serious nuclear accidents, it should also be used in nuclear medicine.     

Population dose near the Semipalatinsk test site

To determine the consequences of atmospheric atomic bomb tests for the population in the surroundings of the former nuclear weapons test site near Semipalatinsk in Kazakhstan, a pilot study was performed by an international cooperation between Kazakh, French, Czech and German institutions at two villages, Mostik and Maisk. Together with Kazakh scientists, eight experts from Europe carried out a field mission in September 1995 to assess, within the framework of a NATO supported project, the radiological situation as far as external doses, environmental contamination and body burden of man were concerned. A summary of the results obtained is presented. The actual radiological situation near the test site is characterized by fallout contaminations. Cs was found in upper soil layers in concentrations similar to those of the global fallout. Also Sr, Am and Co were observed. The resulting present dose to the population is low. Mean external doses from soil contamination for Maisk and Mostik (0.60–0.63 mSv/ year) presently correspond to mean external doses in normal environments. Mean values of the annual internal doses observed in these two villages are below 2 μSv/year for ⁹⁰Sr. For other radionuclides the internal doses are also negligible. Received: 12 March 1998 / Accepted in revised form: 1 August 1998     

Internal Radiation Exposure Dose in Iwaki City,Fukushima Prefecture after the Accident at Fukushima Dai-ichi Nuclear Power Plant

As a result of the accident at the Fukushima Daiichi Nuclear Power Plant (FNPP) on 11 March 2011, a huge amount of radionuclides, including radiocesium, was released and spread over a wide area of eastern Japan. Although three years have passed since the accident, residents around the FNPP are anxious about internal radiation exposure due to radiocesium. In this study, we screened internal radiation exposure doses in Iwaki city of Fukushima prefecture, using a whole-body counter. The first screening was conducted from October 2012 to February 2013, and the second screening was conducted from May to November 2013. Study participants were employees of ALPINE and their families who underwent examination. A total of 2,839 participants (1,366 men and 1,473 women, 1–86 years old) underwent the first screening, and 2,092 (1,022 men and 1,070 women, 1–86 years old) underwent the second screening. The results showed that 99% of subjects registered below 300 Bq per body in the first screening, and all subjects registered below 300 Bq per body in the second screening. The committed effective dose ranged from 0.01–0.06 mSv in the first screening and 0.01–0.02 mSv in the second screening. Long-term follow-up studies are needed to avoid unnecessary chronic internal exposure and to reduce anxiety among the residents by communicating radiation health risks.     

Ionizing radiation and risk of chronic lymphocytic leukemia in the 15-country study of nuclear industry workers

In contrast to other types of leukemia, chronic lymphocytic leukemia (CLL) has long been regarded as non-radiogenic, i.e. not caused by ionizing radiation. However, the justification for this view has been challenged. We therefore report on the relationship between CLL mortality and external ionizing radiation dose within the 15-country nuclear workers cohort study. The analyses included, in seven countries with CLL deaths, a total of 295,963 workers with more than 4.5 million person-years of follow-up and an average cumulative bone marrow dose of 15 mSv; there were 65 CLL deaths in this cohort. The relative risk (RR) at an occupational dose of 100 mSv compared to 0 mSv was 0.84 (95% CI 0.39, 1.48) under the assumption of a 10-year exposure lag. Analyses of longer lag periods showed little variation in the RR, but they included very small numbers of cases with relatively high doses. In conclusion, the largest nuclear workers cohort study to date finds little evidence for an association between low doses of external ionizing radiation and CLL mortality. This study had little power due to low doses, short follow-up periods, and uncertainties in CLL ascertainment from death certificates; an extended follow-up of the cohorts is merited and would ideally include incident cancer cases.     

Pilot study of the Urals population by tooth electron paramagnetic resonance dosimetry

During 1949–1956, about 76 × 10⁶ m³ of radioactive liquid waste containing a total activity of 10¹⁷ Bq was discharged into the Techa River by the first Russian industrial nuclear facility Mayak. As a consequence, the population living in the river valley received considerable internal and external radiation doses. The results of a first application of electron paramagnetic resonance (EPR) of tooth enamel for a retrospective individual dose evaluation of the residents of the Techa riverside are presented. Three main contributions to the dose absorbed in tooth enamel have been considered: external exposure mainly from the Techa River sediments, internal exposure mainly due to ⁹⁰Sr; and background radiation including all other sources of exposure except the Techa River. The teeth of 86 inhabitants of the town Kamensk-Uralskii were analysed to determine the age-dependent contribution of the background radiation to the enamel dose. For 22 residents of the middle and lower Techa riverside, measurements of the ⁹⁰Sr whole-body content and EPR measurements of the absorbed dose in enamel were used to establish a correlation between these two quantities. Finally, absorbed doses in the enamel of five residents of the upper Techa riverside were determined by the EPR method. Contributions of the background radiation and the internal ⁹⁰Sr contamination were subtracted to determine the external exposure of the residents.     

Measurement of Individual Doses of Radiation by Personal Dosimeter Is Important for the Return of Residents from Evacuation Order Areas after Nuclear Disaster

To confirm the availability of individual dose evaluation for the return of residents after the accident at the Fukushima Dai-ichi Nuclear Power Plant (FNPP), we evaluated individual doses of radiation as measured by personal dosimeters in residents who temporarily stayed in Evacuation Order Areas in Kawauchi village, which is partially located within a 20 km radius of the FNPP. We also compared individual doses with the external radiation doses estimated from the ambient dose rates and with doses estimated from the concentrations of radionuclides in the soil around each individual’s house. Individual doses were significantly correlated with the ambient doses in front of the entrances to the houses (r = 0.90, p<0.01), in the backyards (r = 0.41, p<0.01) and in the nearby fields (r = 0.80, p<0.01). The maximum cumulative ambient doses in the backyards and fields around the houses were 6.38 and 9.27 mSv/y, respectively. The maximum cumulative individual dose was 3.28 mSv/y, and the median and minimum doses were 1.35 and 0.71 mSv/y. The estimated external effective doses from concentrations of artificial radionuclides in soil samples ranged from 0.03 to 23.42 mSv/y. The individual doses were moderately correlated with external effective doses in the backyards (r = 0.38, p<0.01) and in the fields (r = 0.36, p<0.01); however, the individual doses were not significantly correlated with the external effective doses in front of the entrances (r = 0.01, p = 0.92). Our study confirmed that individual doses are low levels even in the evacuation order area in Kawauchi village, and external effective dose levels are certainly decreasing due to the decay of artificial radionuclides and the decontamination of contaminated soil. Long-term follow-up of individual doses as well as internal-exposure doses, environmental monitoring and reconstruction of infrastructure are needed so that residents may return to their hometowns after a nuclear disaster.     

A cytogenetic study of nuclear power plant workers using the micronucleus-centromere assay.

A cytogenetic study was performed in 215 nuclear power plant workers occupationally exposed to radiation using the micronucleus-centromere assay for peripheral blood lymphocytes. As control population served administrative staff with yearly doses below 1 mSv. The increase of the micronucleus frequency with age, observed in the non-smoking control population, is mainly due to an enhanced number of centromere-positive micronuclei, pointing to an increased chromosome loss. No differences in the number of micronuclei, centromere-positive and centromere-negative micronuclei between smokers and non-smokers are observed. An analysis of the micronucleus data vs. the dose accumulated over the 10 years preceding the venepuncture shows no significant clastogenic or aneuploidogenic effects of the exposure in the studied population which is representative for workers in the nuclear industry at present. According to the linear fits to our data an increase of the micronucleus frequency pro rata 0.5 per 1000 binucleated cells per year, related to the centromere-negative micronuclei, may be expected for workers with the maximal tolerable dose of 20 mSv/year.     

The Semipalatinsk nuclear test site: a first assessment of the radiological situation and the test-related radiation doses in the surrounding territories

As a result of atmospheric nuclear tests at the Semipalatinsk test site `Polygon', adjacent territories were contaminated by radionuclide fallout. The population of some districts in the Semipalatinsk oblast were exposed to elevated levels of radiation. Contamination and exposure mostly resulted from early atmospheric tests. The radiological situation of the Semipalatinsk oblast is described. Effective dose estimates due to external and internal exposure attributable to the 1949 and 1953 tests in villages near the Polygon range from 70 mSv to 4470 mSv. Received: 13 February 1997 / Accepted in revised form: 1 July 1997     

Solid cancer mortality associated with chronic external radiation exposure at the French atomic energy commission and nuclear fuel company

Studies of nuclear workers make it possible to directly quantify the risks associated with ionizing radiation exposure at low doses and low dose rates. Studies of the CEA (Commissariat à l'Energie Atomique) and AREVA Nuclear Cycle (AREVA NC) cohort, currently the most informative such group in France, describe the long-term risk to nuclear workers associated with external exposure. Our aim is to assess the risk of mortality from solid cancers among CEA and AREVA NC nuclear workers and its association with external radiation exposure. Standardized mortality ratios (SMRs) were calculated and internal Poisson regressions were conducted, controlling for the main confounding factors [sex, attained age, calendar period, company and socioeconomic status (SES)]. During the period 1968-2004, there were 2,035 solid cancers among the 36,769 CEA-AREVA NC workers. Cumulative external radiation exposure was assessed for the period 1950-2004, and the mean cumulative dose was 12.1 mSv. Mortality rates for all causes and all solid cancers were both significantly lower in this cohort than in the general population. A significant excess of deaths from pleural cancer, not associated with cumulative external dose, was observed, probably due to past asbestos exposure. We observed a significant excess of melanoma, also unassociated with dose. Although cumulative external dose was not associated with mortality from all solid cancers, the central estimated excess relative risk (ERR) per Sv of 0.46 for solid cancer mortality was higher than the 0.26 calculated for male Hiroshima and Nagasaki A-bomb survivors 50 years or older and exposed at the age of 30 years or older. The modification of our results after stratification for SES demonstrates the importance of this characteristic in occupational studies, because it makes it possible to take class-based lifestyle differences into account, at least partly. These results show the great potential of a further joint international study of nuclear workers, which should improve knowledge about the risks associated with chronic low doses and provide useful risk estimates for radiation protection.     

Procédures de ventilation pulmonaire par aérosol Tc-DTPA : contamination aérienne, contaminations interne et cutanée externe des manipulateurs

Efficiency of an optimization procedure of radiation protection measures with lung ventilation by ^99mTc-DTPA aerosol was evaluated by measuring airborne radioactivity and by looking for external and internal contaminations of technologists. Despite numerous precautions, small amounts of radioactivity were airborne in 71.4% of procedures and a small internal contamination of technologists (1.6–881 Bq; median: 36.3 Bq) was found. The latter was highest in case of deficient patient collaboration and with technical incidents. A very low external contamination (0.1-29.1 Bq; median: 0.1 Bq) was demonstrated with 82% of procedures. Estimated effective doses by internal contamination (0.01-6.2 nSv; median 0.3 nSv) was minimal compared with the maximal legally admissible doses for professionally exposed workers (10 mSv/year); it does not represent an excessive irradiation risk.     

Vertical Distribution and Estimated Doses from Artificial Radionuclides in Soil Samples around the Chernobyl Nuclear Power Plant and the Semipalatinsk Nuclear Testing Site

For the current on-site evaluation of the environmental contamination and contributory external exposure after the accident at the Chernobyl Nuclear Power Plant (CNPP) and the nuclear tests at the Semipalatinsk Nuclear Testing Site (SNTS), the concentrations of artificial radionuclides in soil samples from each area were analyzed by gamma spectrometry. Four artificial radionuclides (²⁴¹Am, ¹³⁴Cs, ¹³⁷Cs, and ⁶⁰Co) were detected in surface soil around CNPP, whereas seven artificial radionuclides (²⁴¹Am, ⁵⁷Co, ¹³⁷Cs, ⁹⁵Zr, ⁹⁵Nb, ⁵⁸Co, and ⁶⁰Co) were detected in surface soil around SNTS. Effective doses around CNPP were over the public dose limit of 1 mSv/y (International Commission on Radiological Protection, 1991). These levels in a contaminated area 12 km from Unit 4 were high, whereas levels in a decontaminated area 12 km from Unit 4 and another contaminated area 15 km from Unit 4 were comparatively low. On the other hand, the effective doses around SNTS were below the public dose limit. These findings suggest that the environmental contamination and effective doses on the ground definitely decrease with decontamination such as removing surface soil, although the effective doses of the sampling points around CNPP in the present study were all over the public dose limit. Thus, the remediation of soil as a countermeasure could be an extremely effective method not only for areas around CNPP and SNTS but also for areas around the Fukushima Dai-ichi Nuclear Power Plant (FNPP), and external exposure levels will be certainly reduced. Long-term follow-up of environmental monitoring around CNPP, SNTS, and FNPP, as well as evaluation of the health effects in the population residing around these areas, could contribute to radiation safety and reduce unnecessary exposure to the public.