Natural radioactivities in iron and nickel ores imported into Japan and the dose assessment for workers handling them.

Japan imports Fe and Ni ores from abroad for use as industrial raw materials in the manufacture of industrial products like stainless steel. Some of these ores might contain high levels of radioactivity, and then workers handling them would be exposed to radiation without being aware of it. Activity concentrations in these ores should be measured to evaluate the radiation exposure of workers. In this study, Fe and Ni ores used as industrial raw materials were collected from iron and steel companies, and the activity concentrations of the (238)U series, the (232)Th series and (40)K in these ores were determined using inductively coupled plasma mass spectrometry (ICP-MS) and gamma ray spectrometry. The activity concentrations of the (238)U series, the (232)Th series and (40)K in these ores samples were lower than the International Atomic Energy Agency (IAEA) values. The doses to workers handling these ores were estimated using methods for dose assessment given in a report by the European Commission. In each scenario, a maximum value of the annual effective dose to workers was estimated to be about 6.8 × 10(-6) Sv, which was lower than intervention exemption levels (annual dose 1.0 × 10(-3) Sv) given in International Commission on Radiological Protection (ICRP) Publication 82.

Variable Strength in Thoron Interference for a Diffusion-Type Radon Monitor Depending on Ventilation of the Outer Air.

Thoron interference in radon measurements using passive diffusion radon detectors/monitors is a crucial problem when it comes to assessing the internal exposure to radon precisely. The present study reported, as one of the potential factors, the effects of air flow conditions on changes in thoron interference. Rates of thoron infiltration (as thoron interference) into the diffusion chamber of the monitor were evaluated. The temporal variation was obtained based on measurements of the underfloor space of a Japanese wooden dwelling using a diffusion-type radon monitor, a reference radon monitor which was not affected by thoron interference, and a thoron monitor. The thoron infiltration rate for the diffusion-type monitor varied from 0% to 20%. In particular, it appeared to increase when ventilation of the underfloor space air was forced. The variable thoron infiltration rate, with respect to ventilation strength, implied that not only a diffusive process, but also an advective process, played a major role in air exchange between the diffusion chamber of the monitor and the outer air. When an exposure room is characterized by the frequent variation in air ventilation, a variable thoron response is considered to occur in radon-thoron discriminative detectors, in which only diffusive entry is employed as a mechanism for the discrimination of radon and thoron.

[Preliminary survey for communicating risk in medical exposure--perception of risk among nurses working in radiology].

A questionnaire survey was conducted on radiation risk and medical exposure, particularly in applications involving children. The survey was targeted at nurses (170 females) engaged in important roles in communicating risk regarding medical exposure. The questionnaire survey yielded the following findings. 1) A significant number of respondents associated the word "radiation" with "cancer treatment," "exposure," and "X-ray pictures." Perceptions about "food exposure" differed between respondents with children and those without. 2) Among the potential health problems posed by radiation, "effects on children," "cancer and leukemia," and "genetic effects" were perceived as the most worrisome. Significant differences in perception were noted regarding infertility between respondents with children and those without. 3) Concerning the effects of medical exposure on fetuses/children, only 10 percent of all respondents replied that they were not anxious about negative effects in either case. Among the respondents who felt uneasy about these aspects, most tended to assess exposed parts, doses, damage potentially suffered, timing of occurrence, and uncertainty, based on their professional experience and knowledge, to rationally distinguish acceptable risks from unacceptable ones and to limit concern to the unacceptable aspects.

Continuous measurements of bronchial exposure induced by radon decay products during inhalation.

The deposition of radon decay products is not equal in each of the respiratory regions and as the presence of radon has been linked with an increase in lung cancer risk, it is important to calculate the deposition of radon decay products in each of the respiratory regions. Recently, many studies on the deposition of radon in respiratory regions have been simulated using wire screens. The systems and equipment used in those studies are not suitable for field measurements as their dimensions are relatively massive, nor can they measure continuously. We developed a continuous bronchial dosimeter (CBD) which is suitable for field measurements. It was designed with specifications that allow it to be remain compact. The CBD simulates the deposition of radon decay products in the different respiratory regions by the use of a combination of wire screens. Deposition in the simulated regions of the lung can be continuously estimated in various environments. The ratio of activities deposited in a simulated nasal cavity (N) and tracheobronchial (TB) regions was calculated from the results of simultaneous measurements using CBD-R (reference), CBD-N (nasal), and CBD-TB (tracheobronchial) measurement units. After aerosols were injected into the radon chamber, the ratio of N and TB depositions decreased. This results indicate that the CBD gave a good response to changes in the environment. It was found that the ratio of N and TB deposition also varied with time in each actual environment.

Investigation of Natural Radioactivity in a Monazite Processing Plant in Japan.

Monazite is a naturally occurring radioactive material that is processed for use in a variety of domestic applications. At present, there is little information available on potential radiation doses experienced by people working with monazite. The ambient dose rate and activity concentration of natural radionuclides in raw materials, products, and dust in work sites as well as the Rn and Rn concentrations in work sites were measured in a monazite processing plant in Japan. Dose estimations for plant workers were also conducted. The activity concentration of the U series in raw materials and products for the monazite processing plant was found to be higher than the relevant values described in the International Atomic Energy Agency Safety Standards. The ambient dose rates in the raw material yard were higher than those in other work sites. Moreover, the activity concentrations of dust in the milling site were higher than those in other work sites. The Rn concentrations in all work sites were almost the same as those in regular indoor environments in Japan. The Rn concentrations in all work sites were much higher than those in regular indoor environments in Japan. The maximum value of the effective dose for workers was 0.62 mSv y, which is lower than the reference level range (1-20 mSv y) for abnormally high levels of natural background radiation published in the International Commission of Radiological Protection Publication 103.

Radon-thoron discriminative measurements in Gansu Province, China, and their implication for dose estimates.

Indoor radon measurements were carried out in cave dwellings of the Chinese loess plateau in Gansu province, where previously the Laboratory of Industrial Hygiene (LIH), China, and the U.S. National Cancer Institute (NCI) had conducted an international collaborative epidemiological study. The LIH-NCI study showed an increased lung cancer risk due to high residential radon levels, and estimated the excess odds ratio at 100 Bq/m3 to be 0.19 (Wang et al., 2002). The present study used two types of newly developed passive monitors: One is a discriminative monitor for radon and thoron; the other is a selective monitor for thoron decay products. The arithmetic mean concentrations of indoor radon and thoron were 91 and 351 Bq/m3, respectively. As reported by our previous study in Shanxi and Shaanxi provinces (Tokonami et al., 2004), the presence of high thoron concentration was confirmed and thoron was predominant over radon in the cave dwellings. However, the mean equilibrium equivalent thoron concentration (EETC) was found to be much lower than expected when assuming the equilibrium factor of 0.1 provided by the UNSCEAR (2000) report. The effective dose by radon and thoron decay products was estimated to be 3.08 mSv/yr. It was significantly lower than the dose of 8.22 mSv/yr estimated from the measurements that did not take into consideration any discrimination between radon and thoron. Excess relative risk of lung cancer per sievert may be much higher than the risk estimated from the LIH-NCI study, considering that discriminative measurements were not used in their study.

Gamma-dose rates from terrestrial and Chernobyl radionuclides inside and outside settlements in the Bryansk Region, Russia in 1996-2003.

In order to estimate current external gamma doses to the population of the Russian territories contaminated as a result of the Chernobyl accident, absorbed gamma-dose rates in air (DR) were determined at typical urban and suburban locations. The study was performed in the western districts of the Bryansk Region within the areas of 30 settlements (28 villages and 2 towns) with the initial levels of 137Cs deposition ranging from 13 to 4340 kBqm(-2). In the towns, the living areas considered were private one-story wooden and stone houses. DR values were derived from in situ measurements performed with the help of gamma-dosimeters and gamma-spectrometers as well as from the results of soil samples analysis. In the areas under study, the values of DR from terrestrial radionuclides were 25+/-6, 24+/-5, 50+/-10, 32+/-6, 54+/-11, 24+/-8, 20+/-6, 25+/-8, and 18+/-5 nGyh(-1) at locations of kitchen gardens, dirt surfaces, asphalt surfaces, wooden houses, stone houses, grasslands inside settlement, grasslands outside settlement, ploughed fields, and forests, respectively. In 1996-2001, mean normalized (per MBqm(-2) of 137Cs current inventory in soil) values of DR from (137)Cs were 0.41+/-0.07, 0.26+/-0.13, 0.15+/-0.07, 0.10+/-0.05, 0.05+/-0.04, 0.48+/-0.12, 1.04+/-0.22, 0.37+/-0.07, and 1.15+/-0.19 microGyh(-1) at the locations of kitchen gardens, dirt surfaces, asphalt surfaces, wooden houses, stone houses, grasslands inside settlement, grasslands outside settlement, ploughed fields, and forests, respectively. The radiometric data from this work and the values of occupancy factors determined for the Russian population by others were used for the assessments of annual effective doses to three selected groups of rural population. The normalized (per MBqm(-2) 137Cs current ground deposition) external effective doses to adults from 137Cs ranged from 0.66 to 2.27 mSvy(-1) in the years 1996-2001, in accordance with professional activities and structures of living areas. For the areas under study, the average external effective doses from 137Cs were estimated to be in the range of 0.39-1.34 mSvy(-1) in 2001. The average external effective doses from natural radionuclides appeared to be lower than those from the Chernobyl fallout ranging from 0.15 to 0.27 mSvy(-1).

Estimating Annual Individual Doses for Evacuees Returning Home to Areas Affected by the Fukushima Nuclear Accident.

To contribute to the reconstruction and revitalization of Fukushima Prefecture following the 2011 nuclear power disaster, annual individual doses were estimated for evacuees who will return home to Tamura City, Kawauchi Village, and Iitate Village in Fukushima. Ambient external dose rates and individual doses obtained with personal dosimeters were measured at many residential and occupational sites throughout the study areas to obtain fundamental data needed for the estimation. The measurement results indicated that the ratio of individual dose based on a personal dosimeter to the ambient external dose measurement was 0.7 with 10% uncertainty. Multiplying the ambient external dose by 0.7 may be an appropriate measure of the effective dose to an individual in the investigated area. Annual individual doses were estimated for representative lifestyles and occupations based on the ambient external dose rates at the measurement sites, taking into account the relationship between the ambient external dose and individual dose. The results were as follows: 0.6-2.3 mSv y in Tamura, 1.1-5.5 mSv y in Kawauchi, and 3.8-17 mSv y in Iitate. For all areas investigated, the estimated dose to outdoor workers was higher than that to indoor workers. Identifying ways to reduce the amount of time that an outdoor worker spends outdoors would provide an effective measure to reduce dose.

Radon and thoron exposures for cave residents in Shanxi and Shaanxi provinces.

Measurements of natural radiation were carried out in cave dwellings distributed in the Chinese loess plateau. Those dwellings are located in Shanxi and Shaanxi provinces. Radon and thoron gas concentrations were measured using a passive integrating radon-thoron discriminative detector. Concentrations of thoron decay products were estimated from measurements of their deposition rates. A detector was placed at the center of each dwelling for 6 months and replaced with a fresh one for another 6 months. Measurements were conducted in 202 dwellings from August 2001 through August 2002. A short-term measurement was conducted during the observation period. In addition, gamma-ray dose rates were measured both indoors and outdoors with an electronic pocket dosimeter. Radioactivities in soil were determined by gamma-ray spectrometry with a pure germanium detector. Among 193 dwellings, indoor radon concentrations ranged from 19 to 195 Bq m(-3) with a geometric mean (GM) of 57 Bq m(-3), indoor thoron concentrations ranged from 10 to 865 Bq m(-3) with a GM of 153 Bq m(-3), and indoor equilibrium equivalent thoron concentrations ranged from 0.3 to 4.9 Bq m(-3) with a GM of 1.6 Bq m(-3). Arithmetic means of the gamma-ray dose rates were estimated to be 140 nGy h(-1) indoors and 110 nGy h(-1) outdoors. The present study revealed that the presence of thoron is not negligible for accurate radon measurements and thus that special attention should be paid to thoron and its decay products for dose assessment in such an environment. More systematic studies are necessary for a better understanding of thoron and its decay products.

Dose estimation by ESR on tooth enamel from two workers exposed to radiation due to the JCO accident.

ESR dosimetry is useful to estimate the external dose for the general population as well as for occupational workers in a nuclear emergency. Three teeth were extracted from two exposed workers (A and B) related to the JCO criticality accident. Tooth enamel was carefully separated from other tooth parts and subjected to ESR dosimetry. Doses equivalent to the gamma-ray dose of 60Co were estimated as follows: for worker A, the buccal and lingual sides of the eighth tooth in the upper right side, 11.8 +/- 3.6 and 12.0 +/- 3.6 Gy, respectively; for worker B, the buccal and lingual sides of the fourth tooth in the upper right side and the fifth tooth in the upper left side, 11.3 +/- 3.4 and 10.8 +/- 3.3 Gy, 11.7 +/- 3.5 and 11.4 +/- 3.4 Gy, respectively. The estimated doses were found to be similar and not dependent on the tooth positions, whether the buccal or lingual sides in each tooth.

Activity concentration of natural radioactive nuclides in nonmetallic industrial raw materials in Japan.

Natural materials such as rock, ore, and clay, containing natural radioactive nuclides are widely used as industrial raw materials in Japan. If these are high concentrations, the workers who handle the material can be unknowingly exposed to radiation at a high level. In this study, about 80 nonmetallic natural materials frequently used as industrial raw materials in Japan were comprehensively collected from several industrial companies, and the activity concentrations of (238)U series, (232)Th series and (40)K in the materials was determined by ICP-MS (inductively-coupled plasma mass spectrometer) and gamma ray spectrum analyses. Effective doses to workers handling them were estimated by using methods for dose estimation given in the RP 122. We found the activity concentrations to be lower than the critical values defined by regulatory requirements as described in the IAEA Safety Guide. The maximum estimated effective dose to workers handling these materials was 0.16 mSv y(-1), which was lower than the reference level (1-20 mSv y(-1)) for existing situation given in the ICRP Publ.103.

Methodological extensions of meta-analysis with excess relative risk estimates: application to risk of second malignant neoplasms among childhood cancer survivors treated with radiotherapy.

Although radiotherapy is recognized as an established risk factor for second malignant neoplasms (SMNs), the dose response of SMNs following radiotherapy has not been well characterized. In our previous meta-analysis of the risks of SMNs occurring among children who have received radiotherapy, the small number of eligible studies precluded a detailed evaluation. Therefore, to increase the number of eligible studies, we developed a method of calculating excess relative risk (ERR) per Gy estimates from studies for which the relative risk estimates for several dose categories were available. Comparing the calculated ERR with that described in several original papers validated the proposed method. This enabled us to increase the number of studies, which we used to conduct a meta-analysis. The overall ERR per Gy estimate of radiotherapy over 26 relevant studies was 0.60 (95%CI: 0.30-1.20), which is smaller than the corresponding estimate for atomic bomb survivors exposed to radiation as young children (1.7; 95% CI: 1.1-2.5). A significant decrease in ERR per Gy with increase in age at exposure (0.85 times per annual increase) was observed in the meta-regression. Heterogeneity was suggested by Cochran's Q statistic (P < 0.001), which may be partly accounted for by age at exposure.

Invited article: in situ comparison of passive radon-thoron discriminative monitors at subsurface workplaces in Hungary.

During a one-year long measurement period, radon and thoron data obtained by two different passive radon-thoron discriminative monitors were compared at subsurface workplaces in Hungary, such as mines (bauxite and manganese ore) and caves (medical and touristic). These workplaces have special environmental conditions, such as, stable and high relative humidity (100%), relatively stable temperature (12°C-21°C), low or high wind speed (max. 2.4 m s(-1)) and low or elevated aerosol concentration (130-60,000 particles m(-3)). The measured radon and thoron concentrations fluctuated in a wide range among the different workplaces. The respective annual average radon concentrations and their standard deviations (in brackets) measured by the passive radon-thoron discriminative monitor with cellulose filter (CF) and the passive radon-thoron discriminative monitor with sponge filter (SF) were: 350(321) Bq m(-3) and 550(497) Bq m(-3) in the bauxite mine; 887(604) Bq m(-3) and 1258(788) Bq m(-3) in the manganese ore mine; 2510(2341) Bq m(-3) and 3403(3075) Bq m(-3) in the medical cave (Hospital Cave of Tapolca); and 6239(2057) Bq m(-3) and 8512(1955) Bq m(-3) in the touristic cave (Lake Cave of Tapolca). The respective average thoron concentrations and their standard deviation (in brackets) measured by CF and SF monitors were: 154(210) Bq m(-3) and 161(148) Bq m(-3) in the bauxite mine; 187(191) Bq m(-3) and 117(147) Bq m(-3) in the manganese-ore mine; 360(524) Bq m(-3) and 371(789) Bq m(-3) in the medical cave (Hospital Cave of Tapolca); and 1420(1184) Bq m(-3) and 1462(3655) Bq m(-3) in the touristic cave (Lake Cave of Tapolca). Under these circumstances, comparison of the radon data for the SF and CF monitors showed the former were consistently 51% higher in the bauxite mine, 38% higher in the manganese ore mine, and 34% higher in the caves. Consequently, correction is required on previously obtained radon data acquired by CF monitors at subsurface workplaces to gain comparable data for SF monitors. In the case of thoron, the data were unreliable and no significant tendency was seen during the comparison therefore comparison of previously obtained thoron data acquired by either CF or SF is doubtful. There was probable influence by relative humidity on the detection response; however, the effects of the high wind speed and elevated aerosol concentration could not be excluded. The results of this study call attention to the importance of calibration under extreme environmental conditions and the need for using reliable radon-thoron monitors for subsurface workplaces.

Occupational exposure to natural radiation in zirconium refractory plants in Japan.

The authors measured the ambient dose rate and activity concentration of natural radionuclides in raw materials, products, and aerosols on worksites, as well as the (222)Rn and (220)Rn concentrations in an unshaped refractory, a shaped refractory, and an electrocast refractory plant processing zirconium ore in Japan. Estimations were made of the effective doses to plant workers. The activity concentration of the (238)U series in raw materials and products in the refractory plants was higher than the critical values (10 Bq g(-1) for (40)K and 1 Bq g(-1) for all other radionuclides of natural origin) specified in the International Atomic Energy Agency Safety Guide. The ambient dose rate in the raw material warehouse of the electrocast refractory plant was 0.75 µSv h(-1), which was the highest among all the worksites at all the refractory plants studied. The activity concentrations of aerosols in the product-output site of the unshaped refractory plant was 0.0015 Bq m for U and 0.00078 Bq m(-3) for (232)Th, which were the highest of all the worksites for all refractory plants. The indoor (222)Rn and (220)Rn concentrations in all worksites of all the refractory plants were almost the same levels as those in everyday indoor places in Japan. The maximum value of the effective dose to workers was 430 µSv y(-1), which was lower than the intervention exemption level (1,000 µSv y(-1)) specified in ICRP Publication 82.

Activity concentration of natural radionuclides and radon and thoron exhalation rates in rocks used as decorative wall coverings in Japan.

In Japan, many dwellings have decorative wall coverings made from granite, andesite, tuff, gabbro, and marble. However, information regarding activity concentrations and radon (Rn) and thoron (Rn) exhalation rates for such rocks is very scarce. Therefore, samples of the granite, andesite, tuff, and marble that are used as wall coverings in Japan were collected from mining companies, and their activity concentrations and Rn and Rn exhalation rates were measured. Dose estimations for inhabitants living in houses built with these materials were also carried out. The activity concentration of natural radionuclides in all the materials was lower than the critical values described by the International Atomic Energy Agency (IAEA) (10,000 Bq kg for K and 1,000 Bq kg for all other radionuclides of natural origin). The maximum values of Rn and Rn mass exhalation rates for the granite samples were 0.12 and 430 mBq kg s, and those for the area exhalation rates were 1.8 and 6300 mBq m s, respectively; these values are higher than those for other samples. The maximum value of effective doses to inhabitants was 0.68 mSv y, which is lower than the intervention exemption level (1 mSv y) given in the International Commission on Radiological Protection (ICRP) Publication 82.

Database of the radioactivity of norm used as industrial raw materials.

Most ores used as industrial raw materials are imported mainly because Japan has poor natural resources. The activity concentrations in these materials should be investigated to evaluate the radiation exposure of workers. In this study, imported industrial raw materials were collected, and the activity concentrations in these resources were measured by using inductively coupled plasma mass spectrometry and gamma ray spectrometry. Furthermore,  a database of activity concentrations of NORMs was developed by referring to the measured results as well as referring to the literature, and a database on the web was published. The purpose of the database is to relieve anxieties among the general public and to provide extensive data regarding NORM for researchers and regulators. The database provides more than 900 activity concentrations in worldwide NORMs at no fee. (NORM database; http://www.nirs.go.jp/db/anzendb/NORMDB/ENG/index.php).

Perceived risk of nuclear power and other risks during the last 25 years in Japan.

The present study described the results of three "fixed-point" surveys on perceived risk related to a list of social and individual risk events during 25 years in Japan. Female clerical staff and researchers were asked to rank 30 items related to various types of technologies and human activities according to their subjective judgments on the order of perceived magnitude of risk in 1983, 1992, and 2007. A similar survey was undertaken for Japanese citizens using web-based questionnaires in 2007. In general, the risk perceptions of the Japanese people, irrespective of gender, age, and occupation, have been uniform during the last 25 years. The female clerical staffs have consistently judged nuclear power as most risky during the last 25 years, whereas researchers' judgment fluctuated with events such as the Chernobyl accident. The ranking of the risk of motor vehicles fell during the 25-y period, whereas those of health risks with food preservatives, x-rays, and antibiotics rose transiently in the 1992 survey. During the 15 years from 1992 to 2007, people tended to learn how to accommodate themselves to these technologies with low risks in exchange for high benefits, except in the case of nuclear power. Nuclear power was regarded as a high-risk item by the Japanese even before the Fukushima nuclear power plant accident in March 2011. This partly explains that the crisis inevitably provokes further high risk perception in Japan, although the overall health threat to the human population in Japan is estimated to be relatively limited so far.

Meta-analysis of second cancer risk after radiotherapy among childhood cancer survivors.

Cancer risks among childhood cancer survivors following radiotherapy have not yet been well characterised in terms of radiation dose. A meta-analysis of studies on the excess relative risk per gray (ERR) of second cancer was conducted previously; unfortunately, the small number of eligible studies restricted quantitative evaluations. To solve this problem, a statistical method to calculate ERR estimates from other estimates was developed, and a meta-analysis was conducted again. The PubMed database was searched and 26 relevant studies were identified. ERR estimates were available in 15 studies, and for the other 11 studies, the regression-based model was used to calculate ERR estimates from other estimates. The overall ERR estimate was 0.40, which was much lower than that of atomic bomb survivors exposed as young children. Heterogeneity of the risk among studies was suggested, and a further study is needed to explore the heterogeneity among studies.

Management of cosmic radiation exposure for aircraft crew in Japan.

The International Commission on Radiological Protection has recommended that cosmic radiation exposure of crew in commercial jet aircraft be considered as occupational exposure. In Japan, the Radiation Council of the government has established a guideline that requests domestic airlines to voluntarily keep the effective dose of cosmic radiation for aircraft crew below 5 mSv y(-1). The guideline also gives some advice and policies regarding the method of cosmic radiation dosimetry, the necessity of explanation and education about this issue, a way to view and record dose data, and the necessity of medical examination for crew. The National Institute of Radiological Sciences helps the airlines to follow the guideline, particularly for the determination of aviation route doses by numerical simulation. The calculation is performed using an original, easy-to-use program package called 'JISCARD EX' coupled with a PHITS-based analytical model and a GEANT4-based particle tracing code. The new radiation weighting factors recommended in 2007 are employed for effective dose determination. The annual individual doses of aircraft crew were estimated using this program.