[en] Information about radioactive cesium (¹³⁷Cs) distribution on lands with different uses is necessary for future decontamination works. This study investigated the degree of contamination and factors affecting ¹³⁷Cs accumulation in soils and wild plants in areas of different land use after the Fukushima Nuclear Power accident. We measured the level of ¹³⁷Cs in soils and wild plants in Iitate village and neighboring areas in 2014. Results indicated that ¹³⁷Cs in the agricultural soils was 11-14 kBq kg^-1, while the roadside soil with a high clay content showed the highest concentration (261 kBq kg^-1) and the mountain soil with high soil organic matter showed the lowest concentration (6 kBq kg^-1). The ¹³⁷Cs concentrations in wild plants directly reflected those in their respective soils. The ¹³⁷Cs uptake in wild plants did not differ among plant species grown in the same soil but differed within the same plant species grown in different soils. (author)

[en] In the present study, we reported the investigation of radiocesium migration from steep slope surrounding catchment to water body based on the radiocesium distribution and soil to sediment ratio. It was confirmed that the radiocesium was derived from the Fukushima accident by considering the ¹³⁴Cs to ¹³⁷Cs ratio corrected to the released day which is about 1. We found the higher radiocesium inventory in higher elevation area and steep slope forest catchment, revealing the atmospheric dry initial deposition-derived radiocesium and high retention of the forest zone. The radiocesium distribution data revealed that the radiocesium migrated more from the transition zone to the water body than from forest catchment, and accumulated in the deeper layer of sediment. The lower value of ¹³⁷Cs soil to sediment ratio provided an evidence of radiocesium migration from the catchment and its accumulation in the sediment. The physicochemical property of surface soil was revealed as one of the possible factors of radiocesium high retention in forest catchment. (author)

[en] Strontium-90 (⁹⁰Sr) and cesium-137 (¹³⁷Cs) were released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011. Strontium-90 concentration in environment was extremely lower than that of ¹³⁷Cs in the soil after the FDNPP accident. However, ⁹⁰Sr may induce higher risk of health effect to human than ¹³⁷Cs by considering longer biological half-life of ⁹⁰Sr than ¹³⁷Cs. Moreover, there is not sufficient data on ⁹⁰Sr horizontal and vertical distribution compared to ¹³⁷Cs, which is important for predicting their long-term migration. In the present study, the distribution of ⁹⁰Sr and ¹³⁷Cs in the soils of Kawauchi and Fukushima paddy rice fields was investigated and the migration of ⁹⁰Sr and ¹³⁷Cs in Lake Ogi sediment and its forestry catchment area was studied. A rough relation between ⁹⁰Sr and ¹³⁷Cs levels in soil is shown and such insufficient correlation might be defined by the low ⁹⁰Sr concentration and because of global fallout. Furthermore, ⁹⁰Sr gave higher coefficient of variation in comparison to ¹³⁷Cs, portraying that the movement of ⁹⁰Sr is more affected by the environmental factors rather than ¹³⁷Cs. The depth dependency of ⁹⁰Sr and ¹³⁷Cs in Lake Ogi forestry catchment area is shown for both radionuclides, and the activity concentration decreases with the increase of depth. However, the ⁹⁰Sr infiltrates more to 10 cm soil profile in contrast to ¹³⁷Cs, showing ⁹⁰Sr faster vertical migration than ¹³⁷Cs. Sediment to soil ratio for ⁹⁰Sr reported a higher value than that of ¹³⁷Cs, which possibly depicts more horizontal flowing of ⁹⁰Sr from forest soil to lake sediment than ¹³⁷Cs. Consequently, the higher mobility of ⁹⁰Sr than ¹³⁷Cs was proposed. (author)

[en] Precise ¹⁵²Eu gamma-ray measurements in the granite samples exposed to the Hiroshima atomic bomb require concentrating the europium (Eu) and excluding natural radioisotopes. In this study, an ion exchange method was applied for isolating Eu ions from granite samples at 56 m, 502 m and 818 m distances from the hypocenter. Although the Eu samples included ²³²Th atoms, the ¹⁵²Eu 344 keV gamma-ray full energy peaks were scarcely affected by the gamma rays from the radioisotopes of the thorium series. Almost all of the radioisotopes in the uranium and actinium series were removed. The Eu contents were determined by atomic absorption spectrometry. The ¹⁵²Eu specific radioactivities in the samples at 56 m and 502 m were higher than those inferred from the DS02 calculations. In the sample at 818 m, the measured value was in agreement with the calculated value based on the DS02. Estimations of the atomic bomb radiation doses are necessary for many investigations which attempt to decide the acceptable levels of radiation risk to the public and workers. The results in the present study will be useful for studying the uncertainties of the estimated atomic bomb radiation doses. (author)

[en] Although a variety of radiation-related education courses are provided in universities, information on faculty and student perceptions of radiation risk is limited. To obtain quantitative data on this issue, we conducted a written questionnaire survey at Nagasaki University on the perceived risks of 13 health hazards, of which six related to radiation exposure. The respondents were asked to estimate the risk of the various items to health on a rating scale of 1 to 5. 'Living near a nuclear plant' received the highest rating of 4, followed by 'not using solar UV protection in midsummer'. 'X-ray diagnostic tests' were rated at only 2, which was lower than the rating for 'air travel'. Among the respondents, undergraduate students showed the highest average risk rating across all items followed by nurses, and staff and graduate students, with doctors and dentists producing the lowest scores. These results suggest that level of specialist knowledge is associated with risk perception, and therefore that radiation education should be carefully planned to improve levels of understanding. (author)

[en] The devastating environmental contamination caused by the nuclear disaster at the Fukushima Daiichi Nuclear Power Station of The Tokyo Electric Power Company is exposing the residents of the disaster-affected areas to health risks attributable to radiation exposure, and fear of the development of ¹³¹I-induced thyroid cancer, which is a stochastic effect of radiation and is particularly high. As part of the response to nuclear disasters by the government of the municipality where the nuclear power station is located and in operation and by the governments of neighboring municipalities, it is necessary to conduct thyroid monitoring for the purpose of alleviating the fears of residents of the disaster-affected areas as well as those living in the contaminated, even if only slightly, neighboring areas (local residents). This health monitoring needs to be implemented without delay in the case of a disaster along with dissemination of a portable type thyroid monitoring system available at evacuation centers, etc. for assessing thyroid exposure doses. The establishment of a system for developing personnel ready to perform monitoring is also essential. Assessing thyroid exposure doses is indispensable as a means of assuring local residents not only of safety but also of security from the risks of radiation. To date, contamination has not been detected in people, except for residents contaminated by a large amount of iodine, by employing the mobile type of thyroid monitoring system. However, when local residents seeking security desire thyroid monitoring, it is preferable that a portable type simplified thyroid monitoring system be used as a means of ensuring security against radiation. (author)

[en] The seabed soil was collected at the Soya Strait of Hokkaido in September 2015, and ¹³⁴Cs derived from Fukushima Daiichi Nuclear Power Plant accident was detected at the seabed soil. It was suggested that this ¹³⁴Cs migrated from the Japan Sea to the Okhotsk Sea by the Tsushima Warm Current and the Soya Warm Current. (author)

[en] Radiophotoluminescence (RPL) photography has been proposed for the measurement of the spatial dose distribution of high radiation fields. A pulsed UV-LED illuminator was prepared as an excitation light source for the RPL photography. The fluorescence image of RPL material was observed by a gated intensified CCD camera. In a preliminary experiment, several tens of spherical RPL detectors were placed near an intense ⁶⁰Co source. The pulsed UV-LED illuminator and the gated intensified camera were pulse-operated to obtain the RPL photograph of the ball-shaped RPL detectors. The spatial dose distribution was calculated from the brightness of obtained RPL images. (author)

[en] The airborne dispersion of ²²³Ra and its descendent nuclides from an aqueous ²²³Ra²⁺ solution containing sodium chloride/citrate was investigated. The dispersion of ²²³Ra was not detected, and γ-rays of ²¹¹Pb and ²¹¹Bi caused by the ²¹⁹Rn dispersion were observed by means of γ-ray spectrometry. The detected radioactivity of ²¹¹Pb was found to decrease as the inner diameter of the vessel containing the ²²³Ra solution was decreased because of the decreasing surface area of the solution exposed to the air. The dispersal rate of ²¹⁹Rn from the aqueous solution was determined by the ratio of the number of the dispersed ²¹⁹Rn atoms calculated from the detected radioactivity of ²¹¹Pb on the samples. The values at room temperature were in the range of (1.6 ± 0.1) × 10^-3-(2.0 ± 0.1) × 10^-2. These rates were found to decrease with decreasing exposed surface area of the vessel used. (author)

[en] The contamination of spinach collected immediately following the Fukushima Daiichi nuclear disaster was investigated. The radionuclides deposited in the spinach were ¹³²Te, ¹³¹I, ¹³²I, ¹³⁴Cs, ¹³⁶Cs and ¹³⁷Cs. Only 40% of these radionuclides were removed when the spinach was washed with water or detergent. The two outside leaves of each spinach stump were contaminated with the radionuclides, but the three inside leaves were nearly uncontaminated. The most significant contamination was observed on the concavities, creases, veins and leaf or stem injuries of the spinach. Most of the radionuclides deposited on the surface, leading to a radioactivity concentration of the epidermal tissue 9 times that of the mesophyll tissue. (author)