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Low-background liquid scintillation counter is one of the popular measuring instruments used to investigate tritium radioactivity in environmental media. These instruments require the liquid sample and organic solvent to be mixed for tritium measurement. In the European Union, the registration, evaluation, authorization and restriction of chemicals regulation was established to control the use of chemical substances of very high concern. It is important to find continuously available alternative reagents. In this paper, a performance evaluation was conducted using four scintillation cocktails according to Japanese conventional procedure; although one of them, Gold Star LT2, contains nonylphenol ethoxylate, it will continue to be available for research and development. From the evaluation results it was confirmed that Gold Star LT2 would be a satisfactory alternative scintillator, which is similar performance of Ultima Gold LLT.

In Japan, the deuterium plasma experiment using the Large Helical Device was started at the National Institute for Fusion Science (NIFS) in March 2017 to investigate high-temperature plasma physics and hydrogen isotope effects in research leading towards the realisation of fusion energy. The deuterium plasma experiment produces small amount of tritium by fusion reactions. To understand any impacts by the experiment to the surrounding environment, monthly precipitation samples have been collected at the NIFS site since November 2013 to assess the relationship between isotope composition and chemical species in precipitation including tritium. By comparing data before and after the deuterium plasma experiment start, it was found that tritium released from the main stack of the fusion test facility had no impact on the environment surrounding NIFS.

137Cs in river systems can be taken up by aquatic animals. In this paper, total 137Cs concentration in the Ukedo River system and 137Cs presence in dissolved, acid-soluble and -insoluble fractions in river water samples were determined. Total 137Cs concentration had the maximum value of 2.08 Bq kg−1 below the Ogaki Dam in May 2012. In the base flow condition, > 87% of 137Cs existed in the dissolved state, and the acid-soluble state and the insoluble state were

Researchers have used various methods to obtain the exhalation rates of radon and thoron from soil and building materials. One of the typical methods for radon exhalation rate is the circulation method using an accumulation container, an external or internal sampling pump and a continuous radon monitor. However, it is necessary to consider sampling flow rate if this method is applied to exhalation rate measurement for thoron due to its short half-life. Based on a calibration experiment, the measured thoron concentrations obtained by an electrostatic collection type radon and thoron monitor (RAD7) were found to be influenced strongly by the sampling flow rate. It was also found that the thoron exhalation rate from a soil sample depended on the pressure difference which was proportional to the increasing sampling flow rate. The thoron exhalation rate measured at the generally used sampling flow rate of the internal sampling pump of the RAD7 was overestimated compared with the value at 0 L min−1.

Some areas around the world have anomalies with high natural radiation that may affect public health due to chronic-low-dose radiation exposure. In the paper, we summarized several studies that find Mamuju, Indonesia, a unique high natural radiation area. The majority of the relevant papers are about monitoring, main sources, and influential factors for the enhancement of radon and dose assessments. Under these circumstances, the Mamuju region is regarded as a promising area for conducting epidemiological studies, and it will provide a unique opportunity for improving and expanding low-dose-rate data on human health effects.

In March 2013, increased

TSP and atmospheric 210Pb concentrations were observed at Tsukuba, Japan during July 2001 to March 2005. TSP concentrations ranged from 14.5 to 152.4 µg m−3. 210Pb concentrations ranged from 0.04 to 0.86 mBq m−3 which was low in summer and high in winter to spring. Although TSP concentrations changed annually, 210Pb concentrations had almost the same concentration level and seasonal variation. The correlation coefficient between 210Pb concentration and NO3− concentration was slightly higher than for other ion species. This result indicated that both had been attached to the same particle size and transported to the sampling site.

In a large fusion test facility, when a deuterium-plasma experiment is conducted a small amount of tritium is produced by the d(d, p)t reaction. From the viewpoints of radiation management and public acceptance, the tritium monitoring and recovery systems were developed and installed for the fusion test device. As for the tritium monitoring equipment, an expiratory test system of tritium was utilized for the internal dose assessment of workers. Active tritium samplers were operated continuously to monitor the amount of tritium released from the stack. As for the tritium recovery equipment, an exhaust detritiation system (EDS) for the plasma experiment has been developed and installed at the downstream of the vacuum pumping system in the fusion test device. All of the exhausted tritium from the vacuum vessel was treated by the EDS during the deuterium-plasma experimental campaign. Then, the tritium recovery rate achieved was more than 95%.

222Rn and 226Ra concentrations of less than a few to several thousands of Bq L−1 have been observed in several underground bodies of water around the world. Although regulations for these concentrations in water have been implemented internationally, there are currently no regulations in place in Japan. However, concentrations that exceed these internationally recognized regulatory values have also been observed in Japan. In this study, concentrations in spring water in the northern part of Japan were measured and the effective dose from intake of the water was evaluated. 222Rn concentrations were measured using a liquid scintillation counter, and 226Ra concentrations were measured using a high purity germanium detector after chemical preparation. The measured 222Rn concentrations (=12.7 ± 6.1 Bq L−1) and 226Ra concentrations (−1) did not exceed the reference values set by international and European/American organizations. A conservative estimate of the annual effective ingestion dose of 8 μSv for 222Rn and 226Ra obtained in this study is much smaller than the estimated overall annual effective dose of 2.2 mSv from natural radiation to the Japanese population. However, this dosage accounts for 8% of the WHO individual dosing criteria of 0.1 mSv/year for drinking water.

In order to understand the regional property of tritium concentration in natural water at Hirosaki City, Aomori Prefecture Japan, natural spring water samples were collected from 15 sites in 2016 and tritium concentration was measured by low-level tritium counting procedure using a commercially available solid polymer electrolyte (SPE) tritium enrichment system. The limit of detection of this procedure was approximately 0.06 Bq/L. Findings showed tritium concentrations in natural spring water samples ranged from 0.30 to 0.55 Bq/L with mean value of 0.44±0.08 Bq/L. These results were within the range of reported concentrations in rain and surface and shallow groundwater in Japan including other places of Aomori Prefecture. The presently obtained data could be considered as the background level of the Hirosaki area. The annual effective dose would be negligibly small compared with the annual effective dose limit of 1 mSv, if the committed effective dose equivalent from drinking water to residents was calculated using the highest tritium concentration data.

In the deuterium plasma experiment using Large Helical Device at the National Institute for Fusion Science (NIFS), a small amount of tritium is produced by the D–D fusion reaction. Then, a part of produced tritium is discharged into the environment via a stack. Thus, the atmospheric tritium in the site of NIFS has been monitored before starting the deuterium plasma experiment. The atmospheric tritium concentrations at NIFS were indicated to be background levels in Japan. To investigate the impact of tritium discharged from the stack, the correlation between the atmospheric tritium concentration and the tritium concentration observed in the stack was evaluated, and no significant correlation was found. In addition, the atmospheric tritium concentration at NIFS ranged within the background levels in Japan. Therefore, the impact of discharged tritium from the stack would be negligible in the environment at NIFS.

To understand the behavior of atmospheric 129I that originated from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, activity concentrations of 129I in samples of atmospheric particulate matter (PM), comprising coarse (>1.1 μm) and fine (

Resuspension of 137Cs from the contaminated ground surface to the atmosphere is essential for understanding the environmental behaviors of 137Cs and estimating external and inhalation exposure of residents. Kajino et al. (2016) assessed the 137Cs resuspension flux from bare soil and forest ecosystems in East Japan in 2013 using a numerical simulation constrained by surface air concentration measurements. However, the simulation was found to underestimate the observed deposition amounts by two orders of magnitude. The reason for this underestimation is that the simulation assumed that resuspended 137Cs is carried by submicron aerosols, which have low deposition rates. Based on the observational indications that soil dust and bioaerosols are the major carriers of resuspended 137Cs, a new simulation is performed with higher deposition rates constrained by both surface concentrations and deposition amounts. In the new estimation, the areal total annual resuspension of 137Cs in 2013 is 25.7 TBq, which is equivalent to 0.96 % of the initial deposition (2.68 PBq). Due to the rapid deposition rates, the annual redeposition amount is also large at 10.6 TBq, approximately 40 % of the resuspended 137Cs. The resuspension rate through the atmosphere (0.96 % y−1) seems slow, but it (2.6 × 10−5 d−1) may not be negligibly small compared to the actual decreasing trend of the ambient gamma dose rate obtained in Fukushima Prefecture after the radioactive decay of 137Cs plus 134Cs in 2013 is subtracted (1.0–7.9 × 10−4 d−1): Resuspension can account for 1–10 % of the decreasing rate due to decontamination and natural decay through land surface processes. The current simulation underestimated the 137Cs deposition in Fukushima city in winter by more than an order of magnitude, indicating the presence of additional resuspension sources. The site of Fukushima city is surrounded by major roads. Heavy traffic on wet and muddy roads after snow removal operations could generate superlarge (approximately 100 µm in diameter) road dust or road salt particles, which is not included in the model but might contribute to the observed 137Cs at the site.

The radioactivity of cesium in the water and sediments of two major rivers was measured along with airborne radioactivity in Namie Town, after the recent partial lift on the evacuation order in 2017. The observed concentrations were up to 384 ± 11 mBq/L for 137Cs in unfiltered water and 1.28 ± 0.09 mBq m−3 for 137Cs in air, while the sediment had a maximum of 44,900 ± 23 Bq kg−1 for 137Cs. The potential yearly committed effective dose was estimated based on the data.

Most radiation protection items made from modern lead contain 210Pb. This study estimated the impact on eye lens of radiation derived from the 210Pb in three types of radiation protection glasses. The counts from the glasses were measured using a Geiger–Müeller survey meter. The net count rate was 92 ± 1 cpm at a distance of 0.5 cm for one type of glasses. Additionally, we conducted a qualitative γ-ray spectrum analysis using a high-purity germanium semiconductor detector. The absorbed dose in the eye lens was related to 210Pb and its daughter radionuclide, 210Bi; this dose was calculated by applying dose conversion coefficients provided by the International Commission on Radiological Protection. The absorbed dose rate in eye lens was conservatively calculated to be on the order of 10 nGy/h for the type of glasses containing the most 210Pb. The dose from β-rays accounted for >99%. In addition, we investigated the dose-reduction effect using a thin acrylic plate. The count rate approximately decreased to background level by inserting a plate with a thickness of 1 mm. We conclude that the impact of 210Pb contained in radiation protection glasses is negligibly small, particularly considering the usefulness of the significant external exposure reduction.

To obtain a better understanding of recent tritium concentration and its seasonal cycle in Japan, monthly precipitation samples were collected in Hokkaido, Gifu and Okinawa prefectures from June 2014 to December 2017. The arithmetic mean ( ± standard deviation) of tritium concentrations in precipitation samples from Hokkaido, Gifu and Okinawa were estimated to be 0.62 ± 0.27 Bq L−1, 0.32 ± 0.12 Bq L−1 and 0.13 ± 0.05 Bq L−1, respectively. These results indicate that the concentrations increase with latitude. In addition, the highest and the lowest concentrations appeared in spring and summer, respectively. To clarify the origins and sources of these cycles, further analyses of chemical compositions of precipitation and meteorological conditions are needed.

The activities carried out to obtain public consent for deuterium experiments in LHD, which began in 2017, are reviewed in this paper. In addition, the upgrades and the safety management of LHD for deuterium experiments, including neutron yield measurement system, exhaust detritiation system, institutional regulation for radiation control, and other issues, are briefly presented. During the first campaign of the deuterium experiments in LHD, the shielding of gamma-ray and neutron by the concrete wall of the LHD torus hall was evaluated. Also, the confinement of radioactive isotopes in air inside the torus hall was investigated. No increase of radiation dose was measured outside the torus hall, although the high radiation dose field inside the torus hall was found during deuterium experiments. Therefore, almost all gamma-rays and neutrons were shielded by the concrete wall of the torus hall due to its sufficient thickness of 2 m. The radioactive isotopes in air as well as in other components were well confined in the torus hall. In particular, the pressure control inside the torus hall being lower than outside the torus hall effectively prevented the radioactive isotopes in air from diffusing to the unprescribed area.

Deuterium plasma operations using a large fusion test device have been carried out since 2017 at the National Institute for Fusion Science. A small amount of tritium was produced by the fusion reaction, d(d, p)t. Then, a part of the tritium was released into the environment. Thus, monitoring the level of tritium in the environment around the fusion test facility is important. This is done before starting the deuterium plasma experiment. The environmental tritium concentrations indicated that they are at background levels in Japan. After starting the deuterium plasma experiment, the environmental tritium around the fusion test facility was within the range of environmental variation. This suggests that there was no impact of tritium on the environment during the first deuterium plasma experimental campaign.

The latest car-borne survey was carried out by Hirosaki University in order to grasp the local distribution of the absorbed dose rate in air after the evacuation order was lifted on Namie Town in 2017. The car-borne survey of absorbed dose rate in air was carried out on most of the roads which were accessible by car in Namie Town using a 3-in × 3-in NaI(Tl) scintillation spectrometer. The range of the absorbed dose rate in air was calculated to be 0.041–11 μGy h−1. The distribution maps of the absorbed dose rate in air were drawn based on the data obtained during the surveys in 2011, 2015 and 2017. The comparison of these absorbed dose rates in air suggests that the elevated absorbed dose rate in air in Namie Town caused by the FDNPP accident may be decreasing faster than natural decline which includes weathering effect and physical decay due to the artificial decontamination.

Soil samples from the surface to a 5 cm depth were collected at a residential house in Koriyama City, Fukushima Prefecture using a scraper plate every three months from March 2014 to September 2014 to evaluate the vertical distribution profiles and inventories of 134Cs and 137Cs in soil. The vertical distribution profiles of radiocesium (134Cs and 137Cs) in soil showed that greater than 86% of the total radiocesium was absorbed in the upper 2 cm 3 years after the accident. Radiocesium in the surface layer seems to move to the lower layer over time. The migration of radiocesium in surface layer might be influenced by the ground surface runoff by rainfall. Radiocesium inventories in June increased significantly over the short period between March and June. In contrast, the radiocesium inventories in September did not increase significantly compared to the values in June. Radiocesium resuspension and deposition caused by decontamination work and meteorological events might be one possible reason for the increased radiocesium inventories observed in June.

Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively high exposure to natural radiation. The goals of the present study were to characterize exposure of the entire Mamuju region as a high natural background radiation area (HNBRA) and to assess the existing exposure as a means for radiation protection of the public and the environment. A cross-sectional study method was used with cluster sampling areas by measuring all parameters that contribute to external and internal radiation exposures. It was determined that Mamuju was a unique HNBRA with the annual effective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated. The study results are new scientific data allowing better understanding of health effects related to chronic low-dose-rate radiation exposure and they can be used as the main input in a future epidemiology study., 論文

This paper does not necessarily reflect the views of the International Commission on Radiological Protection. Several radiation monitoring research projects are underway on dose assessment, biological analysis, and risk communication under an agreement with Namie Town. Indoor radon and thoron progeny concentrations have been measured using passive-type monitors to estimate internal doses due to inhalation. In addition, airborne radiocaesium concentrations at five points in Namie Town have been analysed using a high-purity germanium detector to estimate internal doses for comparison with radon. External radiation doses from natural and artificial radionuclides have also been estimated using an in-situ gamma-ray spectrometer. Other support activities are mentioned briefly in this article

A long-term measurement technique of radon exhalation rate was previously developed using a passive type radon and thoron discriminative monitor and a ventilated type accumulation chamber. In the present study, this technique was applied to evaluate the thoron exhalation rate as well, and long-term measurements of radon and thoron exhalation rates were conducted for four years in Gifu Prefecture. The ventilated type accumulation chamber (0.8 × 0.8 × 1.0 m3) with an open bottom was embedded 15 cm into the ground. The vertical distributions of radon and thoron activity concentrations from the ground were obtained using passive type radon-thoron discriminative monitors (RADUETs). The RADUETs were placed at 1, 3, 10, 30, and 80 cm above the ground inside the accumulation chamber. The measurements were conducted from autumn 2014 to autumn 2018. These long-term results were found to be in good agreement with the values obtained by another methodology. The radon exhalation rates from the ground showed a clearly seasonal variation. Similar to findings of previous studies, radon exhalation rates from summer to autumn were relatively higher than those from winter to spring. In contrast, thoron exhalation rates were not found to show seasonal variation.

In this study, to get a better understanding in characterizing groundwater and ensure its effective management, the radon concentrations in water samples were measured through Ryukyu limestone in southern Okinawa Island, Japan. Water samples were collected from a limestone cave (Gyokusendo cave, dropping water) and two springs (Ukinju and Komesu, spring water), and the radon concentrations were measured by liquid scintillation counters. The radon concentrations in the samples from the Gyokusendo cave, and Ukinju and Komesu springs were 10 &plusmn, 1.3 Bq L&minus, 1, 3.2 &plusmn, 1.0 Bq L&minus, 1, and 3.1 &plusmn, 1.1 Bq L&minus, 1, respectively. The radon concentrations showed a gradually increasing trend from summer to autumn and decreased during winter. The variation of radon concentrations in the dripping water sample from the Gyokusendo cave showed a lagged response to precipitation changes by approximately 2&ndash, 3 months. The estimated radon concentrations in the dripping water sample were calculated with the measured radon concentrations from the dripping water obtained during the study period. Based on our results, groundwater in the Gyokusendo cave system was estimated to percolate through the Ryukyu limestone in 7&ndash, 10 days, and the residence time of groundwater in the soil above Gyokusendo cave was estimated to be approximately 50&ndash, 80 days. This work makes a valuable contribution to the understanding of groundwater processes in limestone aquifers, which is essential for ensuring groundwater sustainability.

Ten years have elapsed since the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, and the relative contribution of natural radiation is increasing in Fukushima Prefecture due to the reduced dose of artificial radiation. In order to accurately determine the effective dose of exposure to artificial radiation, it is necessary to evaluate the effective dose of natural as well as artificial components. In this study, we measured the gamma-ray pulse-height distribution over the accessible area of Namie Town, Fukushima Prefecture, and evaluated the annual effective dose of external exposure by distinguishing between natural and artificial radionuclides. The estimated median (range) of absorbed dose rates in air from artificial radionuclides as of 1 April 2020, is 133 (67&ndash, 511) nGy h&minus, 1 in the evacuation order cancellation zone, and 1306 (892&ndash, 2081) nGy h&minus, 1 in the difficult-to-return zone. The median annual effective doses of external exposures from natural and artificial radionuclides were found to be 0.19 and 0.40 mSv in the evacuation order cancellation zone, and 0.25 and 3.9 mSv in the difficult-to-return zone. The latest annual effective dose of external exposure discriminated into natural and artificial radionuclides is expected to be utilized for radiation risk communication.

The 11th Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Thu. 3 Dec.

Mamuju is a region of Indonesia with relatively high exposure to natural radiation. Since 2012, Mamuju has been a uranium and thorium exploration area. Several mapping studies of the region have been carried out to depict NORM (naturally occurring radioactive material) areas and areas with uranium anomalies. This paper is the first study to use radioactivity measurements of laterite and volcanic rocks to determine the characteristics of radionuclides and other mineral measurements, which are essential for categorising Mamuju rocks and exploring the region as a potential mining area. The radioactivity of the samples was measured using a high-purity germanium (HPGe) detector. Furthermore, we used X-ray fluorescence (XRF) to determine the rock mineral composition. Mamuju is anomalous due to its high content of 238U and 232Th concentrations of 539&ndash, 128,699 Bq&middot, kg&minus, 1 (average: 22,882 Bq&middot, 1) and 471&ndash, 288,639 Bq&middot, 1 (average: 33,549 Bq&middot, 1), respectively. The major elements are dominant, including Fe2O3, SiO2, Al2O3, and Na2O, with several other major elements such as MnO, TiO2, and CaO.

Activity concentrations of 234U, 235U, 238U, 226Ra, 228Ra, 222Rn, 210Po, 210Pb, 40K, 3H, 14C, 134Cs and 137Cs were determined in 20 different Japanese bottled drinking water commercially available in Japan. The origins of the mineral water samples were geographically distributed across different regions of Japan. Activity concentrations above detection limits were measured for the radionuclides 234U, 235U, 238U, 226Ra, 228Ra and 210Po. An average total annual effective dose due to ingestion was estimated for adults, based on the average annual volume of bottled water consumed in Japan in 2019, reported to be 31.7 L/y per capita. The estimated dose was found to be below the recommended World Health Organisation (WHO) guidance level of 0.1 mSv/y for drinking water quality. The most significant contributor to the estimated dose was 228Ra.

Non-Exchangeable Organically Bound Tritium (Nx-OBT) in a biological reference material: NIST 1575a Pine Needles was determined by radiometry and noble gas mass spectrometry. Nx-OBT concentration ranged from 1.08 to 1.45 Bq L−1-combustion water (CW) (n = 4) with mean value (± S.D.) of 1.25 ± 0.15 Bq L−1-CW in radiometry and ranged from 1.12 to 1.35 Bq L−1-CW (n = 3) with mean value of 1.22 ± 0.25 Bq L−1-CW in mass spectrometry. For the Pine Needles reference material, there is no proposed value about Nx-OBT, but our results showed a good agreement with the data determined by different methods. Thus, it is useful material for the quality control of Nx-OBT measurements.

A performance test was carried out using five different gamma-ray spectrometers applicable to thyroid monitoring. The energy resolution and efficiency for 7.6-cm × 7.6-cm NaI(Tl), 5.1-cm × 5.1-cm CeBr3, 3.8-cm × 3.8-cm SrI2(Eu), and 2.5-cm × 2.5-cm SrI2(Eu) gamma-ray scintillation spectrometers and a CdTe gamma-ray semiconductor spectrometer were evaluated using the Oak Ridge Institute for Nuclear Studies thyroid-neck phantom with a mock I source for prompt thyroid monitoring after a nuclear emergency. The respective energy resolutions of the full-energy peak for ~0.360 MeV of 3.8-cm × 3.8-cm SrI2(Eu) and 2.5-cm × 2.5-cm SrI2(Eu) scintillation spectrometers were 4.2% and 4.3%, and these values were very close to the value obtained by the CdTe semiconductor spectrometer. The efficiencies of four of the gamma-ray spectrometers were compared based on the efficiency of the 7.6-cm × 7.6-cm NaI(Tl) scintillation spectrometer at 0 cm from the phantom surface, and these values were ~70% for 5.1-cm × 5.1-cm CeBr3, ~30% for 3.8-cm × 3.8-cm SrI2(Eu), 10% for 2.5-cm × 2.5-cm SrI2(Eu) and 2% for 1-cm × 0.1-cm CdTe. Furthermore, the detection limits at various dose rates for the four gamma-ray scintillation spectrometers were evaluated using the method based on International Organization for Standardization publication ISO 11929:2010.

The caesium retention characteristics of a potassium-nickel hexacyanoferrate resin in a polyacrylnitrile (KNiFC–PAN) matrix were tested in fresh water over the range of 2.5–400 mL min−1. The experimental setup used 2 mL resin and 4-L aliquots of freshwater samples. The results showed nearly 100% retention at speeds below 10 mL min−1, above 80% up to 100 mL min−1, and approached 50% at 400 mL min−1. Using 100 mL min−1 flow rate and KNiFC–PAN resin in a well-type HPGe detector, the minimum detectable concentration was reduced to 3 mBq kg−1 for 4-L aliquots of water samples from the previous 15 mBq kg−1 achieved by Powdex ion-exchange resin and a planar type HPGe detector.

A car-borne survey was carried out in Douala, the largest city in Cameroon to make a detailed distribution map of the absorbed dose rate in the city, to locate the high natural radiation areas useful later to carry out indoor radon, thoron, and thoron progeny measurements. Gamma-ray dose rates were measured using 3-in × 3-in NaI(Tl) detector. Activity concentrations of238U,232Th and40K in soil from Douala city were determined by two methods: the first, usingin situgamma spectrometry and the second, at the laboratory using a NaI(Tl) detector. A heterogeneous distribution of absorbed dose rates in air was observed on the dose rate distribution map, and varies from 29 to 86 nGy h−1with an average of 50 nGy h−1, lower than the world average value of 59 nGy h−1. The activity concentrations with NaI(Tl) detector varied from 18 to 47 Bq kg−1for238U, 21 to 54 Bq kg−1for232Th, and 10 to 410 Bq kg−1for40K with averages of 29, 38, and 202 Bq kg−1respectively, forin situmeasurements. They vary between 29–98 Bq kg−1for238U, 29–92 Bq kg−1for232Th, and 40 to 79 Bq kg−1for40K, with averages of 60, 57, and 56 Bq kg−1respectively for soil samples collected at Douala III subdivision. The highest value of the annual effective dose forin situmeasurements by car was observed at Ndogbong and was found to be 0.7 mSv y−1, higher than the world average value of 0.5 mSv y−1.

A water bubbler system that can distinguish chemical forms of tritium was proposed for long-term tritium monitoring of the exhaust gas of a large fusion test device. The characteristics and performance of the water bubbler system were evaluated under operational conditions and confirmed to be suitable for tritium monitoring. For the tritium measurements, the water bubbler system determined the tritium activity and distinguished the chemical forms of tritium. The tritium activity and chemical forms in the exhaust gas provided helpful information to understand the tritium behavior in the large fusion test device.

The long-lived radioactive iodine ($^{129}$I) is a useful geochemical tracer in the atmospheric environment. We recently observed clear seasonal trends in air concentration and deposition of $^{129}$I in Japan. Using these data, we developed a global atmospheric $^{129}$I transport model to reveal key processes for the global atmospheric $^{129}$I cycle. The model generally reproduced the observed seasonal change in air concentration and deposition of $^{129}$I in Japan, and the global distribution of $^{129}$I concentration in rain as presented in past literature. Numerical experiments changing the intensity of anthropogenic and natural sources were conducted to quantify the impact of anthropogenic sources on the global $^{129}$I cycle. The results indicated that the atmospheric $^{129}$I from the anthropogenic sources was deposited in winter and can be accumulated mainly in the northern part of Eurasia. In contrast, the atmospheric $^{129}$I from the natural sources dominated the deposition in summer. These results suggested that the re-emission process of $^{129}$I from the Earth's surface may be important as a secondary impact of $^{129}$I in the global-scaled environment. Furthermore, although wet deposition dominated the total deposition in the Northern hemisphere, dry deposition regionally and seasonally contributed to the total deposition over arctic and northern part of Eurasia in winter, suggesting that the dry deposition may play a key role in the seasonal change of $^{129}$I deposition in the Northern hemisphere high latitudes., 長寿命放射性ヨウ素($^{129}$I)は、大気環境における放射性核種の有用な地球化学トレーサである。本研究では、$^{129}$Iの大気濃度および沈着の観測を実施し、観測データから大気濃度および沈着の明瞭な季節変動を得た。さらに、大気中の$^{129}$I循環を支配する要因を明らかにすることを目的として、得られた観測データを用いて、移流、乱流拡散、大気沈着、光化学、ガス粒子変換、核燃料再処理工場からの$^{129}$Iの排出、海洋および陸域からの$^{129}$Iの揮発の各物理・化学過程を考慮した全球ヨウ素輸送モデルを開発した。全球ヨウ素輸送モデルは、我々が観測した$^{129}$Iの大気濃度および沈着の季節変動、そして既往文献の$^{129}$Iの降水中濃度の全球分布を良好に再現した。開発した全球ヨウ素輸送モデルを用いて人為起源と自然起源の$^{129}$Iインベントリの強度を変化させる数値実験を実施し、地球全体の$^{129}$I循環に対する人為起源の$^{129}$Iの影響を評価した。その結果、冬季においては、人為起源の$^{129}$Iが主にユーラシアの北部に沈着する可能性があることが示された。一方で、夏季においては、自然起源の$^{129}$Iが北半球中高緯度の沈着に支配的であった。これらの結果は、地球表面からの$^{129}$Iの再飛散過程が全球規模での$^{129}$I循環に重要であることを示唆している。さらに、冬季のユーラシア北部や北極域においては局所的に乾性沈着が寄与しており、乾性沈着が環境中の$^{129}$Iの季節変化に重要な影響を及ぼすことが示唆された。

The Large Helical Device (LHD) successfully started the deuterium experiment in March 2017, in which further plasma performance improvement is envisaged to provide a firm basis for the helical reactor design. Some major upgrades of facilities have been made for safe and productive deuterium experiments. For radiation safety, the tritium removal system, the integrated radiation monitoring system, and the access control system have been newly installed. Each system has new interlock signals that will prevent any unsafe plasma operation or plant condition. Major interlock extensions have been implemented as a part of the integrated radiation monitoring system, which also has an inter-connection to the LHD central operation and control system. The radiation monitoring system RMSAFE (Radiation Monitoring System Applicable to Fusion Experiments) is already operating for monitoring γ(X)-rays in LHD. Some neutron measurements have been additionally applied for the deuterium experiments. The LHD data acquisition system LABCOM can acquire and process 24 h every day continuous data streams. Since γ(X)-ray and neutron measurements require higher availability, the sensors, controllers, data acquisition computers, network connections, and visualization servers have been designed to be duplicated or multiplexed for redundancy. The radiation monitoring displays in the LHD control room have been carefully designed to have excellent visual recognition, and to make users immediately aware of several alerts regarding the dose limits. The radiation safety web pages have been also upgraded to always show both dose rates of γ(X)-rays and neutrons in real time.