Workers must wear a respirator and protective clothing to prevent inhalation and contamination by radioactive materials when carrying out certain inspection, maintenance activities at nuclear facilities and other emergency situations. Temperature and humidity increase with time within the protective clothing during such work. This is because the protective clothing is necessarily impermeable so that heat and perspiration caused by physical labor remain. Therefore, the worker’s body temperature and related heatstroke risk gradually increase. To date, workers wearing the protective clothing have been supervised by time management and individual subjective information. This conventional management method may not efficiently monitor any change of heat load and workers’ related health conditions. We therefore combine objective physiological information (including measured worker’s infrared tympanic temperature and heart rate) with individual subjective information, in order to reduce the risk of heatstroke. To this end, a remote (heat strain) monitoring device has been developed. In this paper, we present an overview of the system, the result of functional and efficiency evalution and operational results obtained under actual working conditions.

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Mammography is an indispensable test for detecting early-stage breast cancer. In recommendations issued by the International Commission on Radiological Protection (ICRP) in 2007, the tissue-weighting factor was increased to 0.12 from the figure of 0.05 recommended in 1990. Research is therefore required to elucidate and optimize the dose received by patients during mammography. Most mammography devices incorporate automatic exposure control systems (AECs) to optimize dose and image quality. The aim of this study was to evaluate AECs at the same thickness and composition by using 80 mammography imaging devices (21 models made by seven manufacturers) currently in use, and to assess the dose received by patients during mammography in different institutions. AEC evaluation was performed by using a quality control 156 phantom and dose evaluation by using a polymethylmethacrylate phantom, and the average glandular dose was calculated from the irradiation conditions obtained. The results showed a 3.5-fold difference in average glandular dose, from 0.83 mGy to 2.90 mGy, when the 156 phantom was used. This rose to 4.38-fold for a 60-mm PMMA phantom. It was also shown that differences in dose arise from variations in pressure and detector position.

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The precise energy-dependent response curve of the imaging plate to low-energy photons was obtained by reciprocally combining a calculation and an experiment. The calculation was carried out using the Monte Carlo particle transportation code EGS5. The experiment was carried out using monochromatic photons at the photon factory in KEK. Initially, there was a discrepancy between the calculation and the experiment because of light attenuation in the phosphor layer in the read-out process. However, by setting the attenuation coefficient of this light attenuation to 0.013 μm^-1 and decreasing the imaging plate (IP) response exponentially with depth from the phosphor surface, it was indicated that the calculation result basically follows the experimental result. By using the response curve obtained in this paper, radiation dose can be evaluated accurately in the dose estimation using IP.

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A pre-etching step is applied with carbon dioxide (hereafter, CO₂ pre-etching) of a solid state nuclear track detector (SSNTD) to improve the sensitivity for protons detection. In this study, we quantitatively estimated the sensitization of SSNTD with CO₂ pre-etching to improve the sensitivity of a personal neutron dosimeter. We measured the etch pit size and the critical angle using a 1.7 MV tandem accelerator at the University of Tokyo to evaluate the proton sensitivity. In addition, we calculated the neutron energy response of SSNTD with a polyethylene radiator with the particle and heavy ion transport system multipurpose three-dimensional Monte Carlo code. To evaluate the accuracy of these calculations, neutron energy responses of SSNTD with and without CO₂ pre-etching were measured at the Facility of Radiation Standards of the Japan Atomic Energy Agency. The neutron energy responses calculated by the above Monte Carlo code agreed with the experimental results to within 35%. The results obtained in this research indicate that CO₂ pre-etching at a pressure of 0.6 MPa for 3 days increases the radiator effect by up to 250% for the 5 and 14.8 MeV neutrons.

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In mutual review of the contracting state based on IAEA international agreement in 2005, the Japanese government have received comment that total exposed dose of nuclear power plants in Japan has a different trend compared to other major countries. Analysis focused to the current state was executed based on the report of the annual dose to radiation workers, etc.. As a result, it is clearly that duration of plant operation is shorter than other countries. In other words, inspecting activities, duration of the activity and number of workers is more than other countries. However, annual average dose per radiation worker has been decreasing in recent years owing to continuance dose reduction measures. As a tendency in the near future, annual total dose will increase with large scale of maintenance such as modification for prolonged operation of the preceding plant in the future. On the other hands, there is expectation that new plants have one of the lowest dose is achieved by reflecting the finding of the preceding plant and it is thought that the annual dose per nuclear power plant decreases. This report includes the result of the analysis and measures and the prospect in the future.

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