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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.

In case of nuclear accidents, it is important to determine the magnitude of radiation doses received by people living in contaminated territories. Direct measurement of individual external doses using personal dosimeters (PDs) worn by subjects is the most reliable solution for this necessity. However, it is not practical to expect that all returnees to the affected areas wear PDs. Thus, conversion factors from the ambient dose equivalent (ADEs) to the effective dose for various aged individuals must be determined appropriately. Previous studies demonstrated that the ratio of PDs to ADEs at various areas of Fukushima Prefecture mostly existed in the range of 0.6-0.7 [e.g.,1-3]. These studies provided evidence that PD readings would be reasonable estimators for the effective doses of adult subjects at locations where radioactive cesium is widely and uniformly deposited on the ground. In the present study, we experimentally obtained the response of PDs (D-shuttle, Chiyoda Technol., Tokyo, Japan; Dose i, Fuji Electric, Tokyo, Japan) attached to the front of five age-specific anthropometric phantoms (newborn, 1 y, 5y, 10y and adult male) for lateral radiations of 137Cs with various rotational angles. The PD/ADE ratio for the D-shuttle on the five phantoms with rotational irradiation simulating the exposure in Fukushima Prefecture were 0.87, 0.85, 0.83, 0.83 and 0.77, respectively. The ratio for newborns was 11 % higher than that for adult males. This body size dependency can be explained by the PD response to exposure direction. We discussed the results of this study and our field experiments to construct conversion coefficients from the ADE to the effective doses for age-group residents living in affected areas, which will be presented at the conference., International Conference on Individual Monitoring of Ionising Radiation (IM2022) and Neutron and Ion Dosimetry Symposium (NEUDOS-14)

It is very important to determine the precise internal thyroid doses of Fukushima residents involved in the 2011 Fukushima nuclear disaster, particularly for small children. This has been challenging due to the lack of direct human measurements to identify 131I, the biggest contributor to the thyroid doses. We previously used a dataset of late whole-body counter (WBC) measurements targeting 134Cs and 137Cs for the thyroid dose estimation in comparison with the intake ratios of 131I to 137Cs (or 134Cs) derived from thyroid and whole-body doses individually obtained from different subject groups, assuming simultaneous acute intake via inhalation. Herein, we applied the same method to the doses of residents in Iwaki city (located south of the Fukushima Daiichi Nuclear Power Plant) with a relatively high activity ratio (131I/137Cs) for the ground deposition density. Our analyses revealed that the intake ratio (131I/137Cs) for the Iwaki residents was 4.2–4.3, which is relatively consistent with the values obtained in other studies (average 3.0–5.0). No regional difference in the intake ratios from other areas was observed, but further studies are required to determine the accurate intake ratio in the early phase of the accident, in particular focusing on the reasonable interpretation of results of the late WBC measurements to evaluate the actual Cs intake.

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 thyroid internal doses of Fukushima residents mainly from their intake of 131I due to the lack of direct measurements. Only about 1,300 data of the residents related to 131I have been available, and 1,080 of the data were obtained from the screening campaign that was conducted by the Nuclear Emergency Response Local Headquarter at the end of March 2011 in Kawamata-town, Iwaki-city, and Iitate-village. Here, we reassessed the thyroid doses of the 1,080 subjects aged  15-y-old by using new age-specific conversion factors to determine the 131I thyroid contents from net signals of the devices used, with consideration of the possible uncertainty related to the measurements. The results demonstrated that the thyroid equivalent doses of the subjects were < 30 mSv (excluding outliers). We also demonstrate the 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 131I 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 for Iitate-village were similar to that for Iwaki-city even though the 131I concentration in tap water was much higher in Iitate-village than Iwaki-city. The range of thyroid doses for Minamisoma-city was similar to those for Iitate-village and Iwaki-city, and the range for Fukushima-city was smallest among the five municipalities. Since the major route of intake has remained unclear, this paper presented the plausible upper and lower thyroid doses, between which the actual doses are thought to exist mostly, based on the 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 thyroid internal dose assessment.

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, 131I. In a previous dose estimation, we used the results of whole-body counter (WBC) measurements targeting 134Cs and 137Cs, based on the assumption that these radioisotopes were incorporated at the same time as 131I 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 Cs 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 Cs detection rates (and the 90th percentile values of the 137Cs intake) of the prompt and late evacuees were about 20% (5.4  103 Bq) and 60% (1.6  104 Bq), respectively. Approximately 20% of the individuals analyzed were categorized as late evacuees. These differences in Cs 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.

International Commission on Radiological Protection recommends that aircraft crew and frequent flyers be informed of their individual doses received from cosmic radiation onboard aircrafts. The cosmic radiation dose in aviation is generally assessed by model calculations. In Japan, the code “JISCARD EX” is used since 2007 for management of cosmic radiation exposure of aircraft crew. In the present study, the precision of this code was investigated in regard to neutrons which contribute the most to the effective dose in aviation. Measurements of cosmic neutrons were performed with two moderator-type neutron monitors having different response functions: a conventional-type rem meter (NCN1) and an extended energy-range rem meter (WENDI-II) in four long-haul flights to Singapore, Sydney, Washington, D.C. and London from Japan (Narita or Kansai airport). Through the combined analyses of these measurements, the contribution of high-energy (>15 MeV) neutron component was estimated. The ambient dose equivalents, H*(10), measured with WENDI-II agreed well with the calculations made by JISCARD EX, while the contribution of the high-energy component obtained as the difference between the measured H*(10) values of two monitors was systematically higher than the model calculations.

BACKGROUND Public interest in radiation rose after the Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Station accident was caused by an earthquake off the Pacific coast of Tohoku on March 11, 2011. Various reports on the accident and radiation were spread by the mass media, and people displayed their emotional reactions, which were thought to be related to information about the Fukushima accident, on Twitter, Facebook, and other social networking sites. Fears about radiation were spread as well, leading to harmful rumors about Fukushima and the refusal to test children for radiation. It is believed that identifying the process by which people emotionally responded to this information, and hence became gripped by an increased aversion to Fukushima, might be useful in risk communication when similar disasters and accidents occur in the future. There are few studies surveying how people feel about radiation in Fukushima and other regions in an unbiased form. OBJECTIVE The purpose of this study is to identify how the feelings of local residents toward radiation changed according to Twitter. METHODS We used approximately 19 million tweets in Japanese containing the words “radiation” (放射線), “radioactivity” (放射能), and “radioactive substances” (放射性物質) that were posted to Twitter over a 1-year period following the Fukushima nuclear accident. We used regional identifiers contained in tweets (ie, nouns, proper nouns, place names, postal codes, and telephone numbers) to categorize them according to their prefecture, and then analyzed the feelings toward those prefectures from the semantic orientation of the words contained in individual tweets (ie, positive impressions or negative impressions). RESULTS Tweets about radiation increased soon after the earthquake and then decreased, and feelings about radiation trended positively. We determined that, on average, tweets associating Fukushima Prefecture with radiation show more positive feelings than those about other prefectures, but have trended negatively over time. We also found that as other tweets have trended positively, only bots and retweets about Fukushima Prefecture have trended negatively. CONCLUSIONS The number of tweets about radiation has decreased overall, and feelings about radiation have trended positively. However, the fact that tweets about Fukushima Prefecture trended negatively, despite decreasing in percentage, suggests that negative feelings toward Fukushima Prefecture have become more extreme. We found that while the bots and retweets that were not about Fukushima Prefecture gradually trended toward positive feelings, the bots and retweets about Fukushima Prefecture trended toward negative feelings.

One of the most important lessons learned from the Fukushima Daiichi Nuclear Power Plant accident is that direct (in vivo) measurements of thyroid exposure to radioiodine (mainly, 131I) in the affected populations should be initiated in a timely manner. Furthermore, the existing commercial detectors are not necessarily suitable for the measurement of young children, who are especially vulnerable to radiation exposure and therefore important to screen. This paper presents the development of a new thyroid monitor for such measurements and the results from phantom-based experiments. The monitor has two unique probes having multiple high-energy-resolution type Gd3(Al,Ga)5O12(Ce) (GAGG) detectors that can be placed directly on the young subject's anterior neck. The crystal size of the GAGG detector is 1 cm3, and a probe consisting of a 4 × 1 or 4 × 2 detector array can be selected depending on the subject's body size. The thickness of the 4 × 1 array probe is 24 mm, which is less than that for a conventional NaI(Tl) survey meter having a crystal 1 inch in diameter and 1 inch long (38 mm). Experimental and computational calibrations of the new monitor using existing and virtual phantoms allowed us to determine the full energy peak efficiency for the 131I thyroid contents of different age groups from 3-mo-old to 10-yr-old and minimum detectable activity (MDA) values under various conditions. As a result, the attainable MDA for subjects age ≤5 years under a normal background level (∼0.05 μSv h−1) was found to be ∼30 Bq, which was low enough to identify children with thyroid-equivalent doses over 10 mSv up to about 25 days after the 131I intake. Our new monitor would be useful in direct thyroid measurements for vulnerable young children following a large nuclear accident.

Annual per-capita aviation doses of the Japanese people from commercial flights were calculated for 6 years period from 2009 (solar minimum) to 2014 (solar maximum) using the flight routes provided by major Japanese airlines. For international flights, the area other than Japan was separated to nine regions and collective effective doses were estimated from the number of the Japanese flyers to those regions multiplied by the calculated aviation route doses to representing cities. Collective effective doses for domestic flights were estimated as the products of the collective distances (man km) and the unit-distance route dose determined from three major routes. The flyer-average, annual per-capita dose from the international flights was estimated as 54 μSv and one-flight average dose from the domestic flights was 1.7 μSv. As the Japanese population average, the annual per-capita dose was 8.3 μSv, of which nearly 90% was from the international flights.

One of the most important lessons learned from the Fukushima Daiichi Nuclear Power Plant accident is that direct (in vivo) measurements of thyroid exposure to radioiodine (mainly, 131I) in the affected populations should be initiated in a timely manner. Furthermore, the existing commercial detectors are not necessarily suitable for the measurement of young children, who are especially vulnerable to radiation exposure and therefore important to screen. This paper presents the development of a new thyroid monitor for such measurements and the results from phantom-based experiments. The monitor has two unique probes having multiple high-energy-resolution type Gd3(Al,Ga)5O12(Ce) (GAGG) detectors that can be placed directly on the young subject’s anterior neck. The crystal size of the GAGG detector is 1 cm3, and a probe consisting of a 4 × 1 or 4 × 2 detector array can be selected depending on the subject’s body size. The thickness of the 4 × 1 array probe is 24 mm, which is less than that for a conventional NaI(Tl) survey meter having a crystal 1 inch in diameter and 1 inch long (38 mm). Experimental and computational calibrations of the new monitor using existing and virtual phantoms allowed us to determine the full energy peak efficiency for the 131I thyroid contents of different age groups from 3-mo-old to 10-yr-old and minimum detectable activity (MDA) values under various conditions. As a result, the attainable MDA for subjects age ≤5 years under a normal background level (~0.05 μSv h-1) was found to be ~30 Bq, which was low enough to identify children with thyroid-equivalent doses over 10 mSv up to about 25 days after the 131I intake. Our new monitor would be useful in direct thyroid measurements for vulnerable young children following a large nuclear accident.

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.

Summary: The natural radioactive nuclides especially 210Po, are volatilized at the temperature (600–800 °C) of a burning cigarette and are taken into the human body. Therefore, analysis of natural radioactivity of 210Po in cigarettes and the effective dose to smokers should be evaluated. The activity concentration of 210Po in sixteen brands of Philippine cigarettes was measured by alpha spectrometry, and estimation of effective dose of 210Po to smokers was performed. The activity concentration of 210Po in cigarettes distributed in the Philippines ranged from 5.5 to 17.8 mBq/cigarette and the mean value of their activity concentrations was 12.0 mBq/cigarette. The mean value of annual effective doses of 210Po to smokers obtained from these activity concentrations was 0.021 mSv/y, which was lower than the reference level (1–20 mSv/y) for existing situation in ICRP Publication 103. Keywords: NORM, 210Po, Cigarette, Tobacco

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

Background Public interest in radiation rose after the Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Station accident was caused by an earthquake off the Pacific coast of Tohoku on March 11, 2011. Various reports on the accident and radiation were spread by the mass media, and people displayed their emotional reactions, which were thought to be related to information about the Fukushima accident, on Twitter, Facebook, and other social networking sites. Fears about radiation were spread as well, leading to harmful rumors about Fukushima and the refusal to test children for radiation. It is believed that identifying the process by which people emotionally responded to this information, and hence became gripped by an increased aversion to Fukushima, might be useful in risk communication when similar disasters and accidents occur in the future. There are few studies surveying how people feel about radiation in Fukushima and other regions in an unbiased form. Objective The purpose of this study is to identify how the feelings of local residents toward radiation changed according to Twitter. Methods We used approximately 19 million tweets in Japanese containing the words “radiation” (放射線), “radioactivity” (放射能), and “radioactive substances” (放射性物質) that were posted to Twitter over a 1-year period following the Fukushima nuclear accident. We used regional identifiers contained in tweets (ie, nouns, proper nouns, place names, postal codes, and telephone numbers) to categorize them according to their prefecture, and then analyzed the feelings toward those prefectures from the semantic orientation of the words contained in individual tweets (ie, positive impressions or negative impressions). Results Tweets about radiation increased soon after the earthquake and then decreased, and feelings about radiation trended positively. We determined that, on average, tweets associating Fukushima Prefecture with radiation show more positive feelings than those about other prefectures, but have trended negatively over time. We also found that as other tweets have trended positively, only bots and retweets about Fukushima Prefecture have trended negatively. Conclusions The number of tweets about radiation has decreased overall, and feelings about radiation have trended positively. However, the fact that tweets about Fukushima Prefecture trended negatively, despite decreasing in percentage, suggests that negative feelings toward Fukushima Prefecture have become more extreme. We found that while the bots and retweets that were not about Fukushima Prefecture gradually trended toward positive feelings, the bots and retweets about Fukushima Prefecture trended toward negative feelings.

For the aim of managing the in-flight cosmic radiation exposure of frequent flyers, we have investigated an application of a recently developed electronic personal dosimeter (D-shuttle) for aviation dosimetry. In four long-haul flights between Japan and Germany, it was confirmed that the D-shuttle values were in the range of 25%–30% of the total H*(10) estimated by a route-dose calculation program JISCARD EX. It was found that the values obtained with D-shuttle on the chest were nearly the same with those in a hand luggage placed under the passenger seat, while the values obtained in a suitcase which was placed in the cargo area were notably lower than those in the cabin. According to these findings, it would be possible to monitor the annual aviation doses of frequent flyers by using the D-shuttle dosimeters kept in a hand luggage. Such continuous measurements will also be useful for verification of an unpredicted additional exposure from solar energetic particles.

We developed a new thyroid monitor using multiple high energy resolution Gd3(Al,Ga)5O12(Ce) (HR-GAGG) detectors (each crystal size = 1-cm3), in particular with an intention of measuring small children (including infants) for their internal thyroid exposure from radioiodine following a nuclear accident. The small-sized HR-GAGG detectors allowed to be placed around the human neck at the close distance to increase the geometrical efficiency for 131I localized in the thyroid. We tested two arrangements of the eight HR-GAGG detectors using four age-specific phantoms in each of which a thyroid-shaped container filled with standard 131I solution was installed. The results demonstrated that the minimum detectable activity (MDA) of the new monitor reached 20–30 Bq with a counting time of 180 s, which is significantly lower than that of a conventional NaI(Tl) survey meter (crystal size: 1-inch-dia,1-inch-thick) commonly used for measuring air dose rates.

A new thyroid monitor using multiple high energy resolution Gd3(Al,Ga)5O12(Ce) (HR-GAGG) detectors with each crystal size of one cubic centimeter has been developed, in particular with an intention of measuring small children (including infants) for their internal thyroid exposure from radioiodine following a nuclear accident. The small-sized HR-GAGG detectors allowed to be placed around the human neck at the close distance to increase the geometrical efficiency for 131I localized in the thyroid. An arrangement of eight HR-GAGG detectors surrounding the neck was tested using age-specific phantoms in each of which a thyroid-shaped container filled with standard 131I solution was installed, demonstrating that the minimum detectable activity (MDA) of the new monitor reached 20–30 Bq with a counting time of 180 sec, which was about 10 times lower than that of a conventional NaI(Tl) survey meter (with a crystal size of 1 inch in diameter and 1 inch in thickness) commonly used for measuring air dose rates.

In the aftermath of the 2011 Fukushima nuclear disaster, a screening survey for thyroid internal exposure from intake of radioiodine was performed on 1080 children using handheld NaI(Tl) survey meters. This article presents the design and results of a practical exercise conducted to develop the skills of personnel who would be potentially engaged in such a survey. Participants of this exercise were asked to measure manikin heads in which point sources were installed under normal (~0.05 μSv h−1) and elevated (~0.5 μSv h−1) background conditions. The results demonstrated that the measurements were less dependent on the background radiation level, and the deviation of net signals obtained by the participants were within 10–20% for dose rates above 0.2 μSv h−1. This result suggests that dose rates can be reliably obtained above a provisional operational intervention level for the device, 0.5 μSv h−1 under a real nuclear accident situation.

The radiation environment inside residential houses was measured at MinamiSoma-shi and Iitate-mura in Fukushima Prefecture. The average measured reduction coefficients, which are the ratios of the indoor and outdoor ambient-dose-equivalent rates were 0.35 and 0.45 at the centers of the first and second floors, respectively. The indoor dose rates on the second floors were larger than those on the first floors. The indoor dose rates increased with measurement height. The indoor and outdoor photon energy spectra were measured, revealing that the indoor scattered photon component is larger than the outdoor one.

Twenty-five beauty products known to contain natural radionuclides were collected, and their 222Rn mass exhalation rates were measured. The effective doses to workers due to 222Rn exhaled from these products were estimated. The 222Rn mass exhalation rates of these products were below 177 μBq kg-1 s-1 and were almost identical to those of natural rocks in Japan. The maximum effective dose of 222Rn exhaled from these products was 71 μSv y-1.

After the Fukushima Nuclear Power Plant accident, one of the main issues at stake was the potential intake of contaminated foodstuff by residents of the affected areas. In this context, the importance of the management of the internal exposure by food intake has emerged. For this purpose, a system was developed for estimating the amount of the radioactivity ingested through the diet in order to manage the internal exposure evolution of exposed people. The ultimate goal of this system is to consider all the radiation exposure data including medical exposure in an integrated manner.

Cosmic-ray origin neutrons were measured with a scintillation detector at the summit of Mt. Fuji at an altitude of 3776 m during the summer of 2008. The averaged neutron ambient dose equivalent rate converted from the count rates of the detector was 0.47 (+/-) 0.001 micro Sv/h, which is approximately four times greater than the calculated value of 0.11 (+/-) 0.01 micro Sv/h. It is postulated that the discrepancy between the measured and calculated neutron ambient dose equivalent rates is on account of the additional charged particle component of the mixed radiation field. To examine the characteristics of the detector at high altitude, a simple model equation which relates the count rates of the detector to the calculated fluence rates of cosmic radiation has been supposed. Based on the model equation it is estimated that the neutron ambient dose equivalent rate would be 0.14 (+/-) 0.04 micro Sv/h, and the proton contribution would be 0.28 (+/-) 0.03 micro Sv/h converted as neutron ambient dose equivalent rate. The results agree to the values of the measured and calculated neutron dose equivalent rates, and the discrepancy between them within the errors.

Dose rate of cosmic-ray origin neutrons (abbreviated to “cosmic neutrons”) at aviation altitude was estimated based on the measurements at Mt. Fuji. Cosmic neutrons were measured in a facility of the Mt. Fuji Weather Station located at the summit of Mt. Fuji, the highest mountain in Japan (3776 m in altitude), in the summer of 2008 and 2009. The average of 1 cm ambient dose equivalent H*(10) for two measurements was verified by numerical model simulation and then used to empirically estimate the solar force field potential (FFP). The H*(10) rates at aviation altitude estimated from the measurements at Mt. Fuji were compared to those obtained in in-flight measurements onboard a civilian aircraft flying near Mt. Fuji at the time between the two measurements at the mountain. According to the results obtained, we expect that the empirical estimation based on the measurements at Mt. Fuji will work effectively for dosimetry of cosmic radiation in troposphere.

Information on the accurate spectrum of energetic cosmic-ray particles, particularly neutrons and protons, are important for radiological protection of aircraft crew. However, verification of cosmic radiation doses in aircraft is still difficult because detector signals attributing to different radiation components are mixed and hardly separated by means of a conventional, transportable radiation instrument. We have thus developed a new monitoring system "CREPAS" composed of a phoswich-type scintillation detector coupled with a high-speed data acquisition unit which can measure the waveform of 0 to 5 V signals from -20 to 400ns with 2ns intervals; the waveform data of 12-bit dynamic range are transferred to a personal computer via USB2.0 interface. The signal waveforms are analyzed on site in real time for discrimination of different radiation components such as neutrons, protons, muons/electrons and gamma rays. In order to examine its feasibility, CREPAS was exposed to accelerator beams and then used for cosmic radiation measurements at the summit of a high mountain and in a chartered jet aircraft. It was verified that this system can successfully measure cosmic-ray energetic neutrons (>10MeV) separately from other components. Determination of the precise energy spectra of neutrons and other components calls for further investigation.

Neutron energy spectrum from 7 to 180 MeV, photon energy spectrum from 4 to 50 MeV and proton energy spectrum from 94 to 145 MeV were measured simultaneously using a phoswich-type neutron detector with particle discrimination methods at atmospheric depth of 249 g/cm 2 , a vertical cut-off rigidity of 10.2 GV and at a heliocentric potential of 312 MV. We compared our results with other measured and calculated particle energy spectra. Our measured results give a large, sharp neutron peak around 70 MeV, although Bonner balls show a broad peak around 100 MeV due to low energy resolution. The measured photon and proton spectra are between the calculated energy spectra. This onboard study provides the first experimental neutron energy spectrum over 10 MeV with a high-energy resolution.

Exposure to cosmic radiation in operation of a jet aircraft is considered to be a part of the occupational exposure. Cosmic radiation doses received in aviation are generally evaluated by numerical model simulations. The precision of the model calculation should be verified by measurements. From the viewpoint of radiological protection, neutrons are the most contributing radiation component and have to be precisely measured. Neutron measurements were thus performed in a long-haul flight using a relatively new transportable neutron monitor (WENDI-II) which responds fairly well to the cosmic-ray neutrons. The in-flight measurement was carried out on 5-6 November 2009 on a polar route flight from New York/John F. Kennedy airport to Seoul/Incheon airport. The flying time was ~14 h. The observations obtained as 1 cm ambient dose equivalent were compared with model calculations using a computer program developed by the authors for the calculation of aviation route doses 'JISCARD EX'. Good agreements between the measured and calculated values were observed over the polar route where the geomagnetic cut-off rigidity is the lowest.

The opportunity of exposure to high-energy radiation up to GeV is increasing as in civilian aircrafts and at particle accelerators. The transport of such energetic particle is still difficult to describe precisely and thus verification by measurement using a well characterized instrument is indispensable for reliable dosimetry. However, no reference calibration field has been established for the high-energy range. We thus propose to use a facility at the summit of Mt. Fuji (3776 m in altitude; N35.36°, E138.73°), the highest place in Japan, for characterization of radiation instruments that are possibly used in high-energy radiation fields. For demonstration of the effectiveness, two moderator-type neutron monitors (NCN1 and WENDI-II) having different energy response functions were employed for cosmic-ray neutron measurements in the summer of 2009. In comparison with numerically simulated values, it was found that the extended energy neutron monitor (WENDI-II) has a good property suitable for measurement of the cosmic-ray neutrons with the broad range of energy. The unexpected response of NCN1 is to be investigated in ongoing studies.

A phoswich-type neutron detector was developed in order to measure high-energy cosmic ray neutron spectra in aircraft. The neutron detector consists of an EJ309 organic liquid scintillator that is 121.7mm in diameter and 121.7mm in length and is covered with a 15mm thick EJ299-13 outer plastic scintillator. The neutron response functions of the detector are required for the unfolding method to obtain the energy spectrum. The neutron response functions were created based on MCNPX simulations using an anticoincidence mode with the experimental light-output correlations with particle energies, uniformity of light collection and energy resolutions. The light-output correlation with particle energy, the uniformity of light collection and the energy resolutions were evaluated based on experiments. Measurements of neutron response functions were performed using four quasi-monoenergetic neutron beams from 40 to 80 MeV p-Li reactions to verify the calculated results. The calculated response functions show good agr...

Neutron energy spectrum from 7 to 180 MeV and photon energy spectrum from 4 to 50 MeV were measured onboard an aircraft using a newly developed phoswich-type neutron detector at 10.8 km altitude (atmospheric depth of 249 g/cm2) and geographical latitude of 39°N (a vertical cut-off rigidity of 10.2 GV) near Japan on February 13, 2008 (at a heliocentric potential of 312 MV). Our results were compared with other measurements obtained using 3He-loaded or extended-energy multi moderator neutron spectrometers (Bonner balls) at aviation altitudes, an organic liquid scintillator on the ground, and a double-scatter neutron telescope at the top of the atmosphere and with calculations using the LUIN2000, EXPACS and RMC codes. Our measured results give a large, sharp peak around a neutron energy of 70 MeV, although Bonner balls present a broad peak around 100 MeV due to low energy resolution. Our neutron fluxes agree well with the others. The measured photon energy spectrum is between the LUIN2000- and EXPACS-calcula...

To improve radiation safety in high-energy accelerator facilities, the authors have been developing the new radiation dose monitor device DARWIN: Dose monitoring system Applicable to various Radiations with WIde energy raNges. DARWIN is composed of (a) a phoswitch-type scintillation detector, which consists of liquid organic scintillator BC501A coupled with ZnS(Ag) scintillation sheets doped with 6 Li, and (b) a data acquisition (DAQ) system for digital analysis of the waveform of the scintillator signals. The DAQ system was recently updated in order to apply DARWIN in monitoring dose rates in radiation fields having time structure, introducing an originally developed module based on a field-programmable gate array. To examine the performance of DARWIN placed in radiation fields composed of varieties of particles over wide energy ranges, the authors mounted DARWIN on a jet aircraft and measured neutron, photon, muon, electron, and positron dose rates at high altitudes. The measured dose rates excellently agreed with the corresponding data calculated by EXPACS over a wide altitude range. This agreement indicates the applicability of DARWIN to dose monitoring in complex radiation fields such as those in high-energy accelerator facilities and aircrafts.

Cosmic radiation exposure of aircraft crew, which is generally evaluated by numerical simulations, should be verified by measurements. From the perspective of radiological protection, the most contributing radiation component at aviation altitude is neutrons. Measurements of cosmic neutrons, however, are difficult in a civilian aircraft because of the limitations of space and electricity; a small, battery-operated dosimeter is required whereas larger-size instruments are generally used to detect neutrons with a broad range of energy. We thus examined the applicability of relatively new transportable neutron monitors for use in an aircraft. They are (1) a conventional rem meter with a polyethylene moderator (NCN1), (2) an extended energy-range rem meter with a tungsten-powder mixed moderator (WENDI-II), and (3) a recoil-proton scintillation rem meter (PRESCILA). These monitors were installed onto the racks of a business jet aircraft that flew two times near Japan. Observed data were compared to model calculations using a PHITS-based Analytical Radiation Model in the Atmosphere (PARMA). Excellent agreement between measured and calculated values was found for the WENDI-II. The NCN1 showed approximately half of predicted values, which were lower than those expected from its response function. The observations made with PRESCILA showed much higher than expected values; which is attributable to the presence of cosmic-ray protons and muons. These results indicate that careful attention must be paid to the dosimetric properties of a detector employed for verification of cosmic neutron dose.

放射線医学総合研究所において，サーベイメータ校正と緊急被ばく医療時用線量計の試験を優先目的としたγ線及び中性子線照射場の構築を行った。照射装置には137Cs(7.4MBq，74MBq，740MBq，7.4GBq，74GBq)，60Co(74MBq)，241Am(3.7GBq)，241Am-Be(185GBq)，ダミーの合計9種の線源が装備されている。これまで，照射テーブル上の線量率，線量率の方向依存性及び距離依存性に関して実測による調査を行ってきた。線源から1m位置での1cm線量当量率は，γ線照射時には0.7×10－6から6.9×10－3Svh－1の範囲であり，中性子線照射時は1.3×10－4 Svh－1であることがわかった。γ線源(中性子線源)に対する線量率分布の等方的分布からのずれの大きさは，3％(4％)以内であった。γ線源中心と球形電離箱幾何中心の間の距離に対する線量率の依存性においては，照射テーブル及び壁面からの散乱線の寄与のために逆二乗則からわずかなかい離が見られた。結果として，構築した照射場の性能は優先目的に対する要件を満足するものと考えている。今後の課題は，更に高精度な照射実験を行う利用者のために，照射場の評価，整備を進展させることである。

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 re- turn 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 residen- tial and occupational sites throughout the study areas to obtain fun- damental 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 individ- ual in the investigated area. Annual individual doses were estimated for representative lifestyles and occupations based on the ambi- ent external dose rates at the measurement sites, taking into ac- count the relationship between the ambient external dose and individual dose. The results were as follows: 0.6–2.3 mSv y−1 in Tamura, 1.1–5.5 mSv y−1 in Kawauchi, and 3.8–17 mSv y−1 in Iitate. For all areas investigated, the estimated dose to out- door 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.

Aluminum Oxide is well known as a TLD material for environmental dosemeasurement. The use of aluminum oxide TLD became popular due to its high sensitivity, small fading, and physical stability. However the TL material was not easy to analyze due to thermal quenching and light fading effect. The development of Optically Stimulated Luminescence (OSL) method made Aluminum Oxide simplified the analytical process and equipment. A light emitting diode (LED) stimulation method was developed, which enabled the development of a compact reader, called microStar. This study was conducted to understand the characteristic of low dose measurement using the microStar and its application for environmental dose measurement. OSL dosimeters (OSLD) were irradiated using a 74 GBq and 7.4 GBq Cs-137 radiation source at National Institute of Radiological Science. Irradiations included various delivered doses from 20 KGy to 1 mGy free in air. The microStar gets good read out results. The microStar can be used for environmental dose measurement. Over 10 microStar readers have been deployed around the Fukushima Daiichi Nuclear Power Plant (NPP) for monitoring members of the general public, workers, and environmental dose.

We measured a cosmic-neutron energy spectrum for the energy range from 9 to 160 MeV at the summit of Mt. Fuji at 3776 m above sea level, using a phoswich-type scintillation detector to study high altitude cosmic-ray exposure. Neutron signals from phoswich-type scintillation detector were separated from other particle signals by means of a pulse shape discrimination method, and unfolded with the FERDO-U code. The measured unfolded cosmic-neutron energy spectrum showed two peaks, one at around 20 MeV and the other at 110 MeV. The 110 MeV peak had good energy resolution, and the peak energy and the spectral neutron fluence rate around the peak were in agreement with those of our calculation. On the contrary, the appearance of a 20 MeV peak did not agree with the previous cosmic-neutron spectrum measurements and calculations. We believe that it is due to the overlap of signals of different particles caused by insufficient particle identification.

Mt. Fuji is located approximately 300 km southwest of TEPCO’s Fukushima Daiichi Nuclear Power Plant. We performed the radiation survey along two main Mt. Fuji’s trails from 04:30 to 18:30 on July 9, 2011. We climbed Yoshida trail from Fuji-Subaru Line fifth station (2,300 m in altitude) to Yoshida-Subashiri top (3,720 m in altitude) and descended Subashiri trail from the Yoshida-Subashiri top to Subashiri new fifth station (2,000 m in altitude) on foot while measuring gamma rays. The dose rate 1 m above ground as measured using a NaI(Tl) scintillation survey meter was within the range from 0.03 to 0.05 μSv/h throughout our measuring trip. We used a NaI(Tl) scintillation spectrometer for gamma-ray pulse height spectra measurement. The gamma-ray pulse height spectra obtained at least 2,500 m in altitude on both Yoshida and Subashiri trails showed the peaks of two radioactive cesium isotopes (134Cs and 137Cs) and natural radioactive nuclides. It was confirmed that a radioactive plume released from the Fukushima Daiichi Nuclear Power Plant had arrived at least 2,500 m above sea level of Mt. Fuji.

As a preliminary step for predicting groundwater flow in a plateau 30–50 m above sea level, a model for three-dimensional analysis of groundwater flow was formulated and its validity was verified. The plateau consists of Neogene sedimentary rocks and a Quaternary deposit. Most of the groundwater originates in precipitation, with the groundwater table lying in the Quaternary deposit. Steady-state analysis was conducted by using the finite element method. The results of pore-water pressure measurement and water examination were useful in verifying the validity of the model. In constructing the model, reducing the hydraulic conductivity according to the depth on the basis of the results of the actual measurement was important.

Transition radiation (TR) X-rays are expected to be a highly brilliant X-ray source because the interference among TR X-rays emitted from many thin foils placed periodically in vacuum can increase their intensity and make them quasi-monochromatic. In order to study the interference (resonance) effects of TR, we measured the energy spectra of TR for several sets of thin foil stacks at various emission angles. It was found that the resonance effects of TR are classified into intrafoil and interfoil resonances and the intensity of TR X-rays increases nonlinearly with increasing foil number, attributed to the interfoil resonance. It became evident that the brilliance of TR is as high as that of SR.

[1] Fluctuations of energetic radiation that seemed to be caused by a summer thunderstorm were observed at the top of Mt. Fuji. The largest of such fluctuations was gradual and lasted for about 20 minutes, and was found to be high-energy gamma rays having a continuous energy spectrum up to 10 MeV or more. As for the feature of these fluctuations, it seems naturally that such fluctuations are caused by the bremsstrahlung photons generated by the energetic electrons produced continuously with an intense electric field in the thundercloud rather than originated in the process of lightning discharge.