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Yokoyama, Sumi*; Tsujimura, Norio; Hashimoto, Makoto; Yoshitomi, Hiroshi; Kato, Masahiro*; Kurosawa, Tadahiro*; Tatsuzaki, Hideo*; Sekiguchi, Hiroshi*; Koguchi, Yasuhiro*; Ono, Koji*; et al.
Journal of Radiation Protection and Research, 47(1), p.1 - 7, 2022/03
Background: In Japan, new regulations that revise the dose limit for the lens of the eye (the lens), operational quantities, and measurement positions for the lens dose were enforced in April 2021. Based on the international safety standards, national guidelines, the results of the Radiation Safety Research Promotion Fund of the Nuclear Regulatory Authority, and other studies, the Working Group of Radiation Protection Standardization Committee, the Japan Health Physics Society (JHPS) developed a guideline for radiation dose monitoring for the lens. Materials and Methods: The Working Group of the JHPS discussed the criteria of non-uniform exposure and the management criteria set to not exceed the dose limit for the lens. Results and Discussion: In July 2020, the JHPS guideline was published. The guideline consists of three parts: main text, explanations, and 26 questions. In the questions, the corresponding answers were prepared, and specific examples were provided to enable similar cases to be addressed. Conclusion: With the development of guideline on radiation dose monitoring of the lens, radiation managers and workers will be able to smoothly comply with revised regulations and optimise radiation protection.
Yokoyama, Sumi*; Iwai, Satoshi*; Tsujimura, Norio; Hashimoto, Makoto; Yoshitomi, Hiroshi; Kato, Masahiro*; Kurosawa, Tadahiro*; Tatsuzaki, Hideo*; Sekiguchi, Hiroshi*; Koguchi, Yasuhiro*; et al.
Proceedings of 15th International Congress of the International Radiation Protection Association (IRPA-15) (Internet), 8 Pages, 2022/00
Okuno, Yasuki*; Ishikawa, Norito; Akiyoshi, Masafumi*; Ando, Hirokazu*; Harumoto, Masaki*; Imaizumi, Mitsuru*
Japanese Journal of Applied Physics, 59(7), p.074001_1 - 074001_7, 2020/07
Times Cited Count：3 Percentile：22.52(Physics, Applied)Performance degradation prediction for space solar cells under irradiation with low-energy electrons is greatly affected by displacement threshold energy (Ed) when a displacement damage dose (DDD) model is used. According to recent studies, the Ed of P atoms is much lower than the conventional Ed value in InP-type solar cells irradiated with low-energy electrons. This indicates that the value of Ed typically used in DDD model leads to significant error in performance degradation prediction. In this study, degradation of AlInGaP solar cells is observed after irradiation with 60 keV electrons. The results suggest that the Ed of P atoms in AlInGaP solar cells is much smaller than the conventionally used Ed value. By using the DDD model with the Ed value obtained in this study, we demonstrated that the performance degradation predicted by the DDD model agrees well with the experimental results.
Akiyoshi, Masafumi
JNC TN9400 2004-058, 194 Pages, 2004/03
JNC-TN9400-2004-058.pdf:30.94MB
In this study, swelling, thermal conductivity and mechanical hardness were measured for irradiated ceramics, having different crystallographic structure and chemical bonding. Influence of structural defects on phsical properties were clarified by the evaluation of defect recovery behavior.
Akiyoshi, Masafumi; Akasaka, Naoaki; Tachi, Yoshiaki; Yano, Toyohiko*
Abstract p303,22-P-02, 303 Pages, 2003/00
Focusing on the cover layer materials (as the Radon Barrier Materials), which could have the effect to restrain the radon from scattering into the air and the effect of the radiation shielding, we produced the radon barrier materials with crude bentonite on an experimental basis, using the rotary type comprehensive unit for grinding and mixing, through which we carried out the evaluation of the characteristics thereof.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
Positron annihilation lifetime spectroscopy (PALS) is very strong tool to investigate sab-nanometer scale defects in metals and semiconductors. PALS is based on the 
-ray measurement techniques and it is difficult to measure radioactive samples such as Neutron irradiated samples. Therefore we are creating a method by which you can measure PALS for one very small radioactive sample. It is needed to reject events that positrons annihilate at outside of the sample. We placed the sample at a small space between scintillators and used signals from the scintillators for the anti-coincidence method to reject the events. We succeeded to reject 20% of the events.
Okuno, Yasuki; Kitamura, Akane; Iwamoto, Yosuke; Okubo, Nariaki; Akiyoshi, Masafumi*; Imaizumi, Mitsuru*; Shibata, Yuichi*; Yamaguchi, Masafumi*
no journal, ,
In the vicinity of the reactor core of TEPCO's Fukushima Daiichi Nuclear Power Plant, it is a very high radiation environment due to the accident. In order to investigate the conditions at the inside of the reactor pressure vessele and the building, the current radiation measuring device has limitations in performance and function. Therefore, a simple and highly radiation-tolerant monitor, which can be used under high radiation dose environment, is required. Solar cells are known to be able to measure doses easily. However, the problem is that signals of dose are degraded by radiation damage. In this study, a measurement method of electric current induced by radiaiton and a signal compensation technique applied by a displacement damage prediction model will be reported by using an InGaP solar cell with a high radiation resistance.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
Positron lifetime measurement (PALS) is a useful tool for evaluating nanometer-sized defects in materials such as metals and semiconductors. However, PALS measurement required two flat specimens placed at both sides of the positron source therefore it was difficult to apply PALS for one complicated shaped small specimen. Purpose of this research is developing a PALS method that can be applied for one small specimen having complicated shape. We succeeded to measure PALS spectra with just one specimen.
Ando, Hirokazu*; Yamawaki, Masato*; Hirade, Tetsuya; Akiyoshi, Masafumi*
no journal, ,
The positron lifetime measurement method (PALS) is a useful tool for evaluating nanometer-sized vacancy defects in metals and semiconductors. Especially in the material development for nuclear fusion reactors or nuclear reactors, elucidation of damage behavior by radiation is an important subject. However, PALS always needs to have large enough two specimens. At present, miniaturization of sample is strongly required to reduce radioactivity, but this restriction is a big hindrance to the application of PALS. In this research, we developed a measurement system that can measure positron lifetime with one specimen of arbitrary shape. Positron surrounding the specimen with a scintillator and not incident on the specimen was detected by the light emission of the scintillator, and PALS measurement in the sample was attempted by excluding treatment (anti-coincidence). As a result, we succeeded in obtaining a spectrum which is roughly in agreement with the conventional measurement method.
Okuno, Yasuki; Kitamura, Akane; Ishikawa, Norito; Akiyoshi, Masafumi*; Ando, Hirokazu*; Harumoto, Masaki*; Shibata, Yuichi*; Imaizumi, Mitsuru*; Yamaguchi, Masafumi*
no journal, ,
The displacement damage dose (DDD) for space solar cell is greatly affected by the displacement threshold energy (Ed) during degradation by irradiation with low-energy electrons. In the proposed study, the unpredictable degradation of AlInGaP solar cells in the present DDD model is observed. The findings suggest that the predicted degradation during exposure to low-energy electrons may differ from the actual value. However, it is clarified that if the Ed value is rederived, the nonionizing energy loss can indicate the induced-defect rates in the AlInGaP under irradiation with electrons with a wide range of energy.
Okuno, Yasuki; Okamoto, Tamotsu*; Goto, Yasuhito*; Akiyoshi, Masafumi*; Imaizumi, Mitsuru*; Kobayashi, Tomohiro*
no journal, ,
A solar cell type detector has features such as a thin film structure and no power supply drive by an internal electric field, and it is considered to be useful in a 1 F decommissioning environment. In this presentation, radiation behavior of InGaP and CdTe solar cells with high radiation resistance are reported.
Okuno, Yasuki; Imaizumi, Mitsuru*; Okamoto, Tamotsu*; Kobayashi, Tomohiro*; Akiyoshi, Masafumi*; Goto, Yasuhito*
no journal, ,
In the decommissioning of Fukushima Daiichi Nuclear Power Plant, it is important to specify the distribution and composition of the fuel debris by alpha ray dose analysis. InGaP solar cells is expected to detect alpha-rays because they have the thickness of about one micro meter, which is sufficiently thin with respect to the fly range of alpha-rays. Therefore, the ion irradiation tests with 5 MeV helium was conducted on InGaP solar cells, and the applicability of InGaP solar cells for alpha-ray detector was evaluated and discussed with the results of the experiment and simulation.
Okuno, Yasuki; Imaizumi, Mitsuru*; Okamoto, Tamotsu*; Kobayashi, Tomohiro*; Akiyoshi, Masafumi*; Goto, Yasuhito*
no journal, ,
The Fukushima Daiichi Nuclear Power Station needs to measure the high-level radiation environment near the core, but the ionization chamber, which is the existing product, has limited space where it can be used due to "size", "sensitivity", and "power supply". At present, the information of dose distribution and the estimation of debris position are not sufficiently obtained. Therefore, we have been developing a solar cell type radiation dosimeter as a powerless dosimeter instead of an ionization chamber. In this presentation, we will report on the development of a solar cell self-induced current dosimeter based on the current behavior, degradation behavior, temperature characteristics, etc. that have been elucidated so far.
Okuno, Yasuki; Imaizumi, Mitsuru*; Akiyoshi, Masafumi*
no journal, ,
For space solar cells, a displacement damage dose (DDD) method is currently being constructed for prediction by radiation degradation. As a next-generation space solar cell, InGaP solar cell, which is the top subcell of the InGaP / GaAs / Ge-3 junction type (3J) solar cell, is considered to replace with AlInGaP solar cell. In previous studies, it was reported that the threshold energy (Ed) of P in InP-based solar cell differs by depending on material. Since Ed affects the degradation prediction in the case of incidention of a low energy particle beam, we analyzed the Ed which enables highly accurate of the degradation prediction in AlInGaP solar cells under low energy electron beam irradiation.
