The authors newly developed the deformation adult Japanese male (DJM) and female (DJF) voxel phantoms with eight different body sizes by modifying the average adult Japanese male (JM-103) and female (JF-103) voxel phantoms. These adult Japanese phantoms were used to calculate organ doses due to external photon exposures. The calculated organ doses were compared with those of the ICRP reference male (RCP-AM) and female (RCP-AF) phantoms with standard Caucasian physiques. The perimeters such as bust, chest, waist and hip of DJM and DJF were adjusted to the length, which were calculated by adding or subtracting n standard deviation (σ) units to or from the averages of adult Japanese. The DJM and DJF with perimeters, which difference with Japanese average was n σ units, were named the DJMn σ and DJFn σ (n =-3 ~ +5), respectively. The physiques of DJMn σ and DJFn σ were corrected to the average heights or weights of the adult Japanese. In most cases, the organ doses of DJM-2 σ, DJM+2 σ, DJF-2 σ and DJF+2 σ agreed with those of RCP-AM and RCP-AF within 10% for ISO geometry at 0.3 MeV. The body mass indices (BMIs) of DJM-2 σ or DJF-2 σ and DJM+2 σ or DJF+2 σ are approximately equal to 18 and 28, respectively. Approximately 90% of adult Japanese male or female correspond to BMI range of 18 to 28. It can be concluded that the impact of body size variations of adult Japanese on application of organ doses by RCP-AM and RCP-AF to dose assessment for radiation protection is not significant.
External exposure of workers engaging demolition works of damaged buildings performed near the Fukushima Daiichi Nuclear Power Plants was investigated. Indoor air dose rates recorded near the ceiling were higher than those recorded near the floor, and smaller than outdoor air dose rates. It was found that demolition works at “residence restricted area”, in some cases, might meet specified high dose rate works, because average air dose rate of a demolition work performed in this area exceeded 2.5 µSv/h. Average daily external exposure of workers at residence restricted area was 6.4 µSv, it was higher than that at “zone in preparation for the lifting of the evacuation order,” 4.4 µSv. It may reflect air dose rates recorded at these areas. On the other hands, average cumulative external exposure at “zone in preparation for the lifting of the evacuation order” was 146 µSv, it was higher than that at “residence restricted area,” 89 µSv. This tendency may reflect a long period of demolition work and less of the workers. In demolition works at “zone in preparation for the lifting of the evacuation order,” “removing roofing tiles” was selected as the work which significantly increased external exposures by multiple regression analysis. “Removing interior materials” was also selected as the work which significantly decreased external exposures in demolition works at “residence restricted area.”
Although many radiation epidemiological studies have been carried out, there is still uncertainty about the health effects of low dose and low dose-rate radiation in humans. One reason for this uncertainty is that the risk of radiation itself may be too small to detect. Another possible reason is that the main components of cohorts or statistical method vary in each study. Comparing the Excess Relative Risks (ERRs) with other studies is often one approach; however, few studies have denoted the validity of comparing ERRs. To verify the differences in study methods, we summarized them and the results of radiation epidemiological studies to date. Some of these studies targeted high background residents or patients who received CT scans. In the present work, we focused on cohort studies among nuclear industry workers because they assured more accurate dose measurements and had no possibility of reverse causation (i.e., patients who received CT scans had worse health conditions, which prompted the need for the scans). In addition, we limited the studies to those that summarize derived excess relative risks of mortality based on a linear model.
The result of the environmental monitoring has been evaluated by the “normal range” which was set using by the past measurement values, by referring to the guidance of the environmental monitoring defined by the former nuclear safety commission. The level of the ambient dose and a part of the radioactive concentration in environmental samples had been increased by the radioactive materials accidentally released from the Fukushima Daiichi Nuclear Power Plant since March 2011, so the “normal range” was not revised after 2011. Thus, we investigated the setting method for the “normal range” after the accidental release, to set “normal range” using the measurement data obtained until 2015, and to apply it to the data in 2016 which had no influence from the Tokai reprocessing plant. As a result, most of the data was included in the “normal range.” The “normal range” by this method will be applied to the environmental radiation management report based on the law, and be used to evaluate the measurement value.
Since the discovery of X-rays in 1895, radioactivity and its effects on the body have led to the issue of radiation injury. Radiation-related casualties following exposure to a lethal dose of ionizing radiation show severe acute radiation syndromes (ARS) involving bone marrow death and gastrointestinal death. ARS causes a decrease in the peripheral blood cell count and gastrointestinal dysfunction, consequently leading to death caused by immune deficiency. In cases involving many patients such as severe ARS, the intake of appropriate medications is the most suitable initial treatment. Therefore, the development of effective radiation-protective agent is an important issue against radiological accidents and nuclear threats. In this review, the overview of radiation-protective/mitigative agent development against acute radiation effects (external exposure), as well as our research data, and the prospects for future research have been outlined.
Radon emanation means the escape of radon atoms from solid grains into pore space; it is the very first process that may lead to radon exposure in the environment. Experimental and numerical studies of radon emanation have been diligently carried out since its recognition as a carcinogen. Our previous review of the measured data showed a wide range of radon emanation fractions from natural substances, and then we discussed the effects of environmental factors such as pore water. The present paper provides an overview of the approaches and progress of radon emanation modeling that may be useful for the interpretation of measured data. Recoil and/or diffusion of radon in solid following alpha decay of radium, which underlies the mechanisms of radon emanation, have been incorporated into numerical models. In the calculation based on recoil-based emanation, radium distribution and pore size were the most important parameters, which govern the magnitudes of radon ejections from the birth grain and of radon embedding into another solid surface, respectively. The solid diffusion appeared significant only at a temperature higher than several hundred degrees Celsius. A model is now desired to be developed that incorporates the transport process of radon atoms that are still settled in solid after alpha recoil, considering radiation damage and its resulting inner path network.
The reopening of the research reactor at Kyoto University required regular calibration of many personal dosimeters. However, it is not practical to subscribe to a calibration service for all the dosimeters. Traceability to the Japanese National Standard is transferred to a representative dosimeter with 137Cs and 60Co radioactive sources by the service. Here, we show a method to simultaneously confirm the accuracy of 100 dosimeters by using the transfer dosimeter in an irradiation field of a 226Ra radioactive source. The background in the 2.9-m × 4.0-m × 3.3-m chamber was 0.001 mSv day-1, and thus had no effect on calibrations. The position dependence of dose equivalents from the source at the centre of the chamber was an inverse square of distances for the primary rays and was inconsequential for scattered rays. The angular dependence around a 44-cm-radius from the source was isotropic. After an irradiation time of 48 minutes, the average difference in readings between the transfer dosimeters and others arranged in the circle was 1.3%, and each difference was within the ± 10% error range stipulated by the manufacturer. These results demonstrate that this irradiation field is ideal for the metrological confirmations of multiple personal dosimeters.