Improved data analysis techniques for calculating more accurate radon and thoron exhalation rates from building interior solid walls.

The impacts of mathematical models and associated parameters on radon (222Rn) and thoron (220Rn) exhalation rates based on in-situ testing at building interior solid walls were demonstrated to improve data analysis techniques. The results showed that the heterogeneity of their activity concentrations within the measurement system was more significant for thoron than radon. The diurnal variation in indoor radon should be considered for better data quality. In conclusion, a model should be appropriately made and selected under the purposes and accuracy requirements of the exhalation test.

Validation study of ambient dose equivalent conversion coefficients for radiocaesium distributed in the ground: lessons from the Fukushima Daiichi Nuclear Power Station accident.

Ambient dose equivalent conversion coefficients (ADCRCs) for converting a radiocaesium inventory to ambient dose equivalent rates (air dose rates) depend on the vertical distribution of radiocaesium in soil. To access the validity of ADCRCs, the air dose rate at 1 m above ground and the vertical distribution of radiocaesium in the soil around the Fukushima Daiichi Nuclear Power Station (FDNPS) present between 2011 and 2019 were measured in the current study. ADCRCs were calculated using air dose rates and three different parameters representing the vertical distribution of radiocaesium in soil: (1) relaxation mass depth (ß), (2) effective relaxation mass depth (ßeff) and (3) relaxation mass depth recommended by the International Commission on Radiation Units and Measurements before the FDNPS accident (ßICRU). When ADCRCs based on ß and ßeff were compared to those based on ß and ßICRU, a positive correlation was found. To confirm the applicability of the ADCRCs based on the three types of ß values, radiocaesium inventories were estimated using the air dose rates and ADCRCs, and the obtained results were compared to the radiocaesium inventory calculated using soil sample measurements. Good agreement was observed between the radiocaesium inventories estimated using the ADCRCs based on ß and ßeff and measured by investigating soil samples. By contrast, the radiocaesium inventory estimated using the ADCRCs based on ßICRU was overestimated compared with that measured by investigating soil samples. These findings support the applicability of ADCRCs based on ß and ßeff in the Fukushima region. Furthermore, the ßICRU result suggests that differences in soil characteristics between Japan and other countries should be considered for evaluating ADCRCs.

Status of radon exposure in Bangladeshi locations and dwellings.

Potentially higher cancer risk due to exposure from natural background radiation was indicated for the Bangladeshi population by estimations based on the countrywide study. Several regions with elevated natural background exhibited higher soil radium and thorium contents than the world average. Being the decay products of these radioactive elements, natural radon isotopes could constitute environmental risk factors for internal radiation exposure to the lungs of people living in these areas. Although lung cancer is one of the most prevalent types of cancer in Bangladesh, its status and features are still unclear. To clarify the present status of one of the potential risk factors for lung cancer in the country, this review intends to ascertain the countrywide radon exposure, and its pathways by types of local dwelling and by regions, which would provide an indication of the internal exposures in areas of elevated natural background radiation and radionuclides of soil as well as an understanding of the preliminary contribution of environmental radon on the country's lung cancer prevalence. In this review, countrywide monitored air radon exposures for Bangladeshi dwellings and workplaces are organized from peer-reviewed published papers. Radon has been identified as one of influential sources of radiation dose in Bangladesh with its higher radon exhalation and emanation rate from soil. A novel nationwide depiction of the overall assessed indoor and soil radon levels for Bangladesh has been made through radiation maps. This would be helpful for designing future systematic radon/radiological monitoring and research on the country's lung cancer prevalence.

DEVELOPMENT OF EMERGENCY MONITORING SYSTEM FOR ALPHA-PARTICLE-EMITTING RADIONUCLIDES IN THE AIR.

During the early phase of a nuclear accident, major radioactive materials are released into the environment, necessitating the prompt deployment of various protective actions to avoid or reduce radiation exposure. To implement these actions, the levels of radioactivity in the environment should be determined. However, the radioactivity concentrations of artificial alpha-particle-emitting radionuclides such as plutonium are difficult to measure in airborne samples, because they are interfered with natural radionuclides such as uranium decay products. Therefore, chemical separation is required to measure the concentrations. This study presents a new emergency monitoring system for airborne samples, which performs multiple-pulse time-interval analysis (MTA) without chemical separation. The system is used in conjunction with an alpha/beta-particle survey meter and adopted an analysis method focusing on the detected time interval of each particle. Its features are that a short time to output measurement result, easy handling and nondestructive. The estimated detection limit of the system was 9.5 × 10-2 Bq m-3. The MTA-based monitoring system could be useful in situations requiring prompt measurement and screening of samples.

PROBABILISTIC ANALYSES OF 131I THYROID ACTIVITY IN PERSONS WITH SURFACE CONTAMINATION IN DIRECT MEASUREMENT WITH A STANDING-TYPE WHOLE-BODY COUNTER AS AN EMERGENCY RESPONSE IN A RADIOLOGICAL INCIDENT.

The authors' previous study suggested that a simple standing-type whole-body counter called FASTSCAN (Canberra, Meriden, CT, USA), widely installed throughout Japan after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, could be used for thyroid measurements in internal dose assessment after a future radiological incident accompanied by the release of 131I into the environment. The present study performed Monte-Carlo simulations using a computational human phantom with several patterns of body surface contamination and used the results to formulate a method for probabilistic analyses of 131I thyroid activity in persons with surface contamination. The major advantage of this method is that the upper limit of the thyroid activity can be determined from the relative frequency distribution without identifying where body surface contamination remains. Therefore, this method is especially effective for use in the early phase of a radiological incident when time and resources are limited, making it difficult to physically remove all body surface contamination for the purpose of gaining more accurate population-wide thyroid screening measurements. As a case study of the FDNPP accident, the proposed method was applied to the results of in vivo measurements for a male subject with body surface contamination. In comparing the probabilistic analyses before and after removal of the subject's contaminated work clothes, the uncertainty of the relative frequency distribution of 131I thyroid activity was reduced by their removal. Therefore, in terms of accurate estimates and avoidance of radiation exposure from their contaminated clothes, efforts to remove body surface contamination still should be made as much as possible in the chaotic situation of the early phase of a radiological incident.

The Effect and Effectiveness of Decontaminating a Pond in a Residential Area of Fukushima.

ABSTRACT: Special reconstruction and revitalization bases were designated in Fukushima's difficult-to-return zone by the Japanese government as targets of intensive decontamination to drastically lower air dose rates and enable residents to return. A pond amid residences of one of these bases was targeted for decontamination, and this study aimed at evaluating the effect and effectiveness of the decontamination using decontamination factor, air dose rate reduction factor, and the additional annual effective dose to residents. Air dose rates were measured in situ with the second-generation Kyoto University Radiation Mapping system, while soil core samples were collected and measured for radioactivity in the laboratory by gamma spectrometry. Lower decontamination factors were observed for more deeply distributed radiocesium soil profiles, whereas areas covered with gravel demonstrated the largest reduction in air dose rates. Decontamination effectively lowered the radiocesium inventory and air dose rates by 51-93% and 37-91%, respectively. Moreover, the additional annual effective dose to the public changed from 1.7 ± 0.79 mSv to 1.2 ± 0.57 mSv because of decontamination representing a dose aversion of 29%. These findings demonstrate how decontaminating ponds in residential areas can help to further lower the external exposure.

The ecological half-life of radiocesium in surficial bottom sediments of five ponds in Fukushima based on in situ measurements with plastic scintillation fibers.

Plastic scintillation fibers (PSFs) have been instrumental in in situ surface contamination surveys post the Fukushima Daichi Nuclear Power Plant accident. Their deployment to monitoring bottom sediments in aquatic environments provides the spatial extent of contamination over wide areas compared to discrete points as provided traditionally by sediment sampling. This study evaluated the wide area ecological half-life (Teco) of radiocesium concentration for surface sediments of five ponds in Fukushima using PSFs, monitoring data generated between 2013 and 2019. The least squares' regression method was employed to evaluate the Teco. Four ponds had a Teco ranging from 3.0 ± 0.3 years to 11.4 ± 2.3 years. A forest-catchment pond exhibited a relatively long Teco of 41.6 ± 55 years. Local variation in the Teco appears to be influenced by sedimentation as we demonstrated larger values for areas showing potential sedimentation in the forest catchment pond. This study demonstrates the importance of wide area in situ monitoring techniques, such as PSF, in providing an overview of the spatial-temporal trends of radiocesium in bottom sediments and confirms the importance of forests as secondary contaminant sources to their drainage.

Difference in the Cesium Body Contents of Affected Area Residents Depending on the Evacuation Timepoint Following the 2011 Fukushima Nuclear Disaster.

Estimating the internal thyroid dose received by residents involved in the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has been a challenging task because of the shortage of direct human measurements related to the largest contributing radioisotope to the dose, I. In a previous dose estimation, we used the results of whole-body counter (WBC) measurements targeting Cs and Cs, based on the assumption that these radioisotopes were incorporated at the same time as I in the early phase of the accident. The main purpose of this study was to clarify whether the trace of the early intake remained in the WBC measurements that were started several months after the accident. In the present work, WBC data of 1,639 persons from Namie town, one of the heavily contaminated municipalities, were analyzed together with their evacuation behavior data. The results demonstrated that the cesium detection rate in the WBC results was several times higher in the late evacuees [who evacuated outside the 20-km radius of the FDNPP at 3:00 p.m. (Japanese Local Time) on 12 March or later] compared to the prompt evacuees (who evacuated before 3:00 p.m. on 12 March). Among the adults, the cesium detection rates (and the 90th percentile values of the Cs intake) of the prompt and late evacuees were about 20% (5.4 × 10 Bq) and 60% (1.6 × 10 Bq), respectively. Approximately 20% of the individuals analyzed were categorized as late evacuees. These differences in cesium would be caused by exposure to the radioactive plume in the afternoon on 12 March, which was likely to influence the late evacuees. On the other hand, the intake on 15 March, when the largest release event occurred, was expected to be relatively small for Namie town's residents. In conclusion, the trace of the early intake remained in the WBC measurements, although this would not necessarily be true for all subjects. The results obtained from this study would provide useful information for the reconstruction of the early internal thyroid doses from radioiodine in the future.

Reassessment of Internal Thyroid Doses to 1,080 Children Examined in a Screening Survey after the 2011 Fukushima Nuclear Disaster.

The dose reconstruction of populations potentially affected by the accident at the Fukushima Daiichi nuclear power plant in March 2011 is of great importance. However, it has been difficult to assess internal thyroid doses to Fukushima residents (mainly from their intake of I) due to the lack of direct measurements. For the residents, only about 1,300 data points related to I are available, and 1,080 of the data points were obtained from the screening campaign that was conducted by the Nuclear Emergency Response Local Headquarters at the end of March 2011 in Kawamata Town, Iwaki City, and Iitate Village. Here, we reassessed thyroid doses to 1,080 subjects aged ≤15 y old using new age-specific conversion factors to determine I thyroid contents from net signals of the devices used, with consideration for the possible uncertainty related to the measurements. The results demonstrated that thyroid equivalent doses to the subjects were <30 mSv (excluding outliers). We also demonstrate dose distributions of each age group from the above three municipalities and those of subjects from Minamisoma City and Fukushima City. One of the findings was that the I intake was similar among different age groups in each of the three municipalities. This was consistent with the assumption that ingestion was a dominant route of intake rather than inhalation. The range of thyroid doses to Iitate Village residents was similar to that to Iwaki City residents even though the I concentration in tap water was much higher in Iitate Village than Iwaki City. The range of thyroid doses to Minamisoma City residents was similar to that to Iitate Village and Iwaki City residents, and the range for Fukushima City residents was smallest among the five municipalities. Since the major route of intake has remained unclear, this paper presents the plausible upper and lower thyroid doses, between which the actual doses are thought to mostly exist, based on two intake scenarios: single inhalation and repeated ingestion. Further research is thus necessary to extract useful evidence from the individual evacuation behaviors for improving the present internal thyroid dose assessment.

EVALUATION AND STATISTICAL ANALYSIS OF THE USE OF INFOGRAPHICS IN RADIOLOGY EDUCATION.

Interest in the need for systematic radiology education has increased since the Fukushima Daiichi nuclear disaster. Practice and attitude surveys on radiology education have been previously undertaken and indicate that there is currently limited quantitative knowledge on the use of radiation and radiological consequences. Although maintenance of an education system and measurements of its effects on knowledge levels have been conducted, no novel developments have been made in the methods of measurement. In this study, we measured the effect of the infographics to develop more effective educational materials and lecture methods in radiology education. In addition, we quantitatively evaluated the effects of using infographics on changes in knowledge levels using statistical analysis.

DEVELOPMENT OF A PELTIER TYPE CLOUD CHAMBER WITH WIDE VIEW FIELD.

Cloud chamber contributes to radiation education by facilitating observation of particle tracks formed by radiation. Peltier-based chamber achieves cooling without the need for dry ice,. we developed a cloud chamber based on peltier thermoelectric modules and has a multilayered heat insulation system to maintain a stable cool environment. It produces sharp particle tracks without requiring a dark room for observing the tracks. Its large top window (diameter of 12.5 cm) provides a relatively wider observation field capable of accommodating five to six students at a time.

RESULTS AND DISCUSSION ON JAPANESE PUBLIC OPINION SURVEYS (2006-17) ABOUT NUCLEAR AND RADIATION APPLICATIONS.

Public opinion on the application of nuclear technology and radiation could change when a nuclear related event occurs. Japan Atomic Energy Relations Organization has tracked its variation through a nationwide opinion survey in Japan by almost the same way every year since FY 2006. We can identify a continuous long-term fluctuation of Japanese opinion before and after the TEPCO Fukushima Daiichi nuclear disaster using the data. In this study we focused on the trends of public opinion for nuclear energy, impressions and knowledge on radiation, and zero-risk request. For example, radiation can be recognised that it is dangerous and complicated matter by Japanese public regardless of that accident. However, a big change of opinions on radiation was shown on the impression for the word of 'Useful' between before and after the accident.

PRELIMINARY TECHNICAL DISCUSSION ON A NEW RADON AND ITS PROGENY CONTINUOUS MONITOR USING TWO-FILTER METHOD.

Focusing on the scalability of Two-Filter Method, we started to develop a monitor for the concentration of radon and its progeny. In this study, we investigated the influence of a high-humidity environment on measuring radon concentration, and the influence of the decay chamber of the monitor on the measurement. In the high-humidity test, the conversion factor of (Bqm-3)/(cpm) tends to raise with increasing humidity. On the measurement of radon progeny, existence of the decay chamber of the monitor makes measurement sensitivity lower under environments of little aerosols. Radon concentration measurement by the developed monitor could be influenced by environmental humidity, and that counting loss could occur due to deposition of radon progeny inside of the decay chamber. Correction relating these would be needed based on the data of calibration tests.

DEVElOPMENT OF DOSE ESTIMATION SYSTEM INTEGRATING SEDIMENT MODEL FOR RECYCLING RADIOCESIUM-CONTAMINATED SOIL TO COASTAL RECLAMATION.

We have developed a dose estimation system integrating assessment methods of radionuclide dispersion in ocean for the case of recycling radiocesium-contaminated soil to coastal reclamation. Radionuclide dispersion in ocean is assessed considering dissolved radionuclide and adsorbed radionuclide on particle by sediment model (OECD/NEA). Time series of Cs-137 dispersion at Fukushima coastal area is assessed by the sediment model and result is almost same with measured value. The major exposure pathways in recycling are estimated by using result of radiocesium dispersion assessment, and internal exposure dose by marine products ingestion is sufficiently lower than external exposure dose of worker.

MCNP SIMULATIONS WITH A PERSONALISED VOXEL PHANTOM TO VERIFY 131I CONTENT IN THYROID ESTIMATED BASED ON MEASUREMENTS WITH AN NaI(Tl) SPECTROMETER.

One of the authors (O.K.) stayed in the area located ~110 km south from the Fukushima Daiichi Nuclear Power Plant during the arrival of radioactive plumes released into the environment due to the accident in March 2011 in Japan. A previous study determined his 131I thyroid content using an NaI(Tl) spectrometer. The one remaining issue was to investigate the measurement error due to inevitable differences in the configuration (e.g. the thyroid shape and volume) between the physical phantom employed for calibration of the spectrometer and the real subject. In the present study, Monte Carlo simulations for the thyroid measurements were performed using the Monte Carlo N-Particle (MNCP) code to investigate discrepancies in peak efficiencies of the spectrometer between the personalised voxel phantom created from O.K.'s magnetic resonance images and the several typical/reference phantoms that exist. As a result, the peak efficiencies for the Oak Ridge Institute of Nuclear Studies (ORINS) phantom were found to be comparable to those for the reference voxel phantoms reproducing realistic human anatomy (the Adult Male phantom and the Japanese Male phantom). The peak efficiency for the personalised phantom, on the other hand, was fairly close to that of the other physical phantom (the Transfer phantom) actually used for the calibration of the spectrometer, suggesting that the 131I thyroid content determined for him in the previous study was sufficiently accurate. The discrepancies of peak efficiencies at the primal photon energy of 131I (365 keV) among the different phantoms were improved by extending the distance between the neck and the spectrometer; however, the appropriate measurement geometry in an actual situation will depend on the primary purpose of the measurements and should be determined accordingly.

Cooperation process between a local government and experts in official voluntary decontamination of environmental radioactivity.

Kashiwa city, inside the Tokyo metropolitan area and located ~200 km south of the Fukushima Dai-ichi Nuclear Power Plant, received a raised environmental ambient radiation dose due to the disaster relative to the rest of area. In this paper, the challenging process of the official voluntary decontamination activity in Kashiwa city, Chiba prefecture, which was carried out with strong cooperation between a local government and experts, is described and reviewed in terms of the effectiveness of the radiation protection. The support system for the official voluntary decontamination work was constructed by the citizens. It was completed within ~15 months after the accident, by way of the following five main steps. (i) A local forum was organized, commencing an open discussion. (ii) (a) Some civic groups started their own activities independent of the national and local governments' policies and measures, and (b) Kashiwa city office held information symposia and risk communication meetings with key persons as a kind of stakeholders as well as education and training of official leaders for voluntary decontamination work. (iii) Joint positive discussion and work projects between civic groups and the local government were started by key personnel. (iv) Local government planned and fixed its official decontamination strategy based on the results of several open discussions. (v) A guidance book for official voluntary decontamination by citizens was distributed by Kashiwa city office. The systematic framework for voluntary decontamination by citizens in Kashiwa city was developed through cooperation between a local government and decontamination experts, which was rare at that time. The authors believe that the process is valuable and should be shared with experts from various fields around the world.

Integrating radiation protection criteria for radioactive waste management into remediation procedures in existing exposure situations after a nuclear accident.

Experience after the accident at the Fukushima Daiichi nuclear power station has shown that there is a need to establish radiation protection criteria for radioactive waste management consistent with the criteria adopted for the remediation of existing exposure situations. A stepwise approach to setting such criteria is proposed. Initially, a reference level for the annual effective dose from waste management activities in the range 1-10 mSv should be set, with the reference level being less than the reference level for the ambient dose. Subsequently, the reference level for the annual effective dose from waste management activities should be reduced in one or more steps to achieve a final target value of 1 mSv. The dose criteria at each stage should be determined with relevant stakeholder involvement. Illustrative case studies show how this stepwise approach might be applied in practice.

Current situations and discussions in Japan in relation to the new occupational equivalent dose limit for the lens of the eye.

Since the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens of the eye in 2011, there have been extensive discussions in various countries. This paper reviews the current situation in radiation protection of the ocular lens and the discussions on the potential impact of the new lens dose limit in Japan. Topics include historical changes to the lens dose limit, the current situation with occupational lens exposures (e.g., in medical workers, nuclear workers, and Fukushima nuclear power plant workers) and measurements, and the current status of biological studies and epidemiological studies on radiation cataracts. Our focus is on the situation in Japan, but we believe such information sharing will be useful in many other countries.

Accurate Measurement of Indoor Radon Concentration using a Low-Effective Volume Radon Monitor.

AlphaGUARD is a low-effective volume detector and one of the most popular portable radon monitors which is currently available. This study investigated whether AlphaGUARD can accurately measure the variable indoor radon levels. The consistency of the radon-concentration data obtained by AlphaGUARD is evaluated against simultaneous measurements by two other monitors (each ~10 times more sensitive than AlphaGUARD). When accurately measuring radon concentration with AlphaGUARD, we found that the net counts of the AlphaGUARD were required of at least 500 counts, <25% of the relative percent difference. AlphaGUARD can provide accurate measurements of radon concentration for the world average level (~50 Bq m-3) and the reference level of workplace (1000 Bq m-3), using integrated data over at least 3 h and 10 min, respectively.