Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
Hoshasen (Internet), 48(2), p.43 - 48, 2023/04
The accident at the Fukushima Daiichi NPP resulted in a large amount of radioactive material being dispersed into the surrounding environment. It is important to understand the radiation distribution in the area, which is still located in the difficult-to-return zone. In this study, a Compton camera and an optical camera were combined to produce a three-dimensional distribution map of source locations and their intensities. Two locations in the difficult-to-return zone (Okuma town) were surveyed: a park parking lot and the area around a private house. The distribution of air dose rates was determined by measurements with a survey meter with a wand-type GPS (Gamma Plotter H manufactured by Nippon Radiation Engineering Co. Measurements were taken with a Compton camera (H420, H3D, USA) at several different positions and angles towards the hotspots. The software (Application Programming Interface Example) allowed real-time confirmation of the radiation incident information (incident time, energy, x, y, z) obtained by the Compton camera. By photographing hotspots in high-dose areas from different positions and angles, the location of the radiation sources and their spatial extent could be confirmed.
Hoshasen Kagaku (Internet), (115), p.43 - 49, 2023/04
Oxidation and dissolution of uranium oxide materials has been a subject of numerous studies as a basis of the geological disposal technology for spent nuclear fuel. The understandings obtained by these studies provide useful suggestions for research and development regarding the retrieval and storage of nuclear fuel debris generated by a nuclear severe accident. Here, these research backgrounds of oxidative dissolution of uranium oxides are briefly reviewed and some studies relating to radiation-induced reactions will be introduced.
Igarashi, Yu; Yamaguchi, Ichiro*; Oda, Keiji*; Fukushi, Masahiro*; Sakama, Minoru*; Iimoto, Takeshi*
Nihon Hoshasen Anzen Kanri Gakkai-Shi, 21(2), p.74 - 76, 2022/11
no abstracts in English
Terasaka, Yuta; Watanabe, Kenichi*; Uritani, Akira*
Hoshasen (Internet), 47(3), p.89 - 96, 2022/10
Kumagai, Yuta; Kusaka, Ryoji; Nakada, Masami; Watanabe, Masayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Sasaki, Takayuki*
Hoshasen Kagaku (Internet), (113), p.61 - 64, 2022/04
The severe accident at TEPCO's Fukushima Daiichi Nuclear Power Station resulted in generation of fuel debris. The fuel debris is in contact with water and the radiolysis of water can accelerate degradation of the debris. The analysis of particles sampled from inside or near the damaged reactors indicates the complicated compositions of the fuel debris. It is challenging to estimate the effect of water radiolysis on such a complicated material. Therefore, in this study, we investigated the potential degradation process by leaching experiments of simulated fuel debris in aqueous HO solution. The results show that the reaction of HO induced uranium dissolution from most of the samples and then formation of uranyl peroxides. In contrast, a sample that had U-Zr oxide solid solution as the major phase exhibited remarkable resistance to HO. These findings revealed that the degradation of the simulated debris reflects the reactivity and stability of the uranium phase in the matrices.
Matsuya, Yusuke; Kai, Takeshi; Ogawa, Tatsuhiko; Hirata, Yuho; Sato, Tatsuhiko
Hoshasen Kagaku (Internet), (112), p.15 - 20, 2021/11
Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo code enabling radiation kinetics, which is often used in diverse research fields, such as atomic energy, engineering, medicine and science. After released in 2010, the PHITS code has been developed to expand its functions and to improve its convenience. In the few years, track-structure mode has been introduced in PHITS that can simulate each atomic interaction by electrons, positions, protons and carbon ions in liquid water. Thanks to the development of track-structure mode, the latest PHITS code enables microscopic dose calculations by decomposing it to the scale of DNA. Aiming at realizing the track-structure mode with high precision, the further developments of electron and ion track-structure mode for arbitrary materials are recently ongoing. This review shows the development history and future prospect of PHITS track-structure mode, which can expect to be further applied to the research fields of atomic physics, radiation chemistry, and quantum life science.
Miyazaki, Yasunori; Sano, Yuichi
Hoshasen Kagaku (Internet), (112), p.27 - 32, 2021/11
no abstracts in English
Hoshasen Seibutsu Kenkyu, 56(3), p.295 - 307, 2021/09
The biological effects of low-dose radiation are confusing due to the various intertwined factors. The vital body responses are complex. In this review, we visualized the results of animal experiments using Self-organizing maps (SOM) and reported the results of the low-dose radiation biological effect assessment from a different viewpoint. For example, although the classification of these data which were the biological effects by low-dose radiation were impossible, SOM got the overall assessment and the intuitive understanding. We reported the results and the usefulness of data visualization of radiation biological effects using machine learning.
Fukunaga, Hisanori*; Matsuya, Yusuke
Hoshasen Seibutsu Kenkyu, 56(2), p.208 - 223, 2021/06
Boron Neutron Capture Therapy (BNCT) is one of the radiation therapies, enabling selectively eradicating tumors by short-range a-particles and Li ions generated through the nuclear reaction between thermal neutron and B within tumor cells. With the development of the accelerator-based neutron source in the recent decades, it is expected that BNCT will be available in many medical facilities worldwide in the future. BNCT irradiation needs a relatively long dose-delivery time after taking up boron drug into tumor cells by intravenous injection. During the period, it is suspected that the boron drug is heterogeneously taken up into cells and its concentration changes continuously, leading to the modification of curative effects from the pharmacological and biological viewpoints. However, the model development for precisely predicting curative effects after BNCT irradiation is still ongoing. Here, we introduce the forefront of model development for estimating the curative effects during BNCT irradiation with high accuracy. This review can create the synergetic effects through an interdisciplinary research approach that can connect the fields of physics, pharmacology, biology and medicine, and would pave the way for new era of BNCT.
Torii, Tatsuo*; Sanada, Yukihisa
Hoshasen, 46(3), p.93 - 101, 2021/05
Ten years have passed since the Fukushima Nuclear Power Plant accident, and various measurements of radiation conditions in the environment are revealing the relationship between changes in trends and their environmental factors. In radiation measurement technology, many new methods have been proposed for environmental measurement and decommissioning after the accident. This paper outlines these latest trends.
Oka, Toshitaka; Takahashi, Atsushi*
Hoshasen Kagaku (Internet), (110), p.13 - 19, 2020/10
The article depicts how to estimate the external exposure dose for wild animals using electron spin resonance (ESR) spectroscopy. The relationship between the CO radical intensity and the absorbed dose, that is, dose response curve of tooth enamel of Japanese macaque was observed, and the detection limit of our method was estimated. The estimated detection limit of 33.5 mGy is comparable to the previously reported detection limit for human molar teeth. The external exposure dose for seven wild Japanese macaques captured in Fukushima prefecture were examined using this dose response curve. The estimated external exposure dose were ranged between 45 mGy to 300 mGy.
Tanaka, Kiriha*; Muto, Jun*; Nagahama, Hiroyuki*; Oka, Toshitaka
Hoshasen Kagaku (Internet), (110), p.21 - 30, 2020/10
In a fault dating by electron spin resonance (ESR), the number of unpaired electrons trapped in defects in minerals contained in a fault material is detected as ESR intensity. Based on the quantitative change of the intensity before and after an earthquake, the last age of a fault movement can be estimated. However, this method has a hypothesis called "zero-setting" which assumes the decrease in the ESR intensity to zero by fault movement during an earthquake. In order to understand and demonstrate zero-setting, the analysis of the natural fault materials and experiments mimicking fault movements have been conducted. In this paper, we summarized the previous studies about zero-setting by fault movement and described the current status and challenges.
Hoshasen Seibutsu Kenkyu, 55(2), p.162 - 172, 2020/06
no abstracts in English
Matsubara, Akihiro*; Fujita, Natsuko; Ishii, Kunikazu*; Kimura, Kenji*
Hoshasen (Internet), 45(3), p.134 - 138, 2020/04
no abstracts in English
Ogawa, Tatsuhiko; Iwamoto, Yosuke
Hoshasen Shahei Handobukku; Oyohen, p.68 - 74, 2020/03
Atomic Energy Society of Japan is going to compile a book entitled "The handbook of radiation shielding -Advanced Edition-" as the guideline for researchers and engineers working on radiation shielding in Japan. The authors are responsible for a chapter dedicated to "Evaluation of observables". Conventionally, in radiation shielding calculation, the quantities averaged over a lot of radiation particles are assessed; however, fluctuation around the average matters for detector response calculation, and radiation-induced damage. Therefore, algorithms to recover the details on fluctuations, such as the event generator mode of PHITS, are needed. This publication is intended to explain the significance of fluctuation evaluation in radiation transport, the principle to calculate the fluctuation, and the effect of the fluctuation on observables.
Hoshasen Shahei Handobukku; Oyohen, p.78 - 83, 2020/03
no abstracts in English
Ogawa, Tatsuhiko; Sato, Tatsuhiko; Yamaki, Tetsuya*
Hoshasen Kagaku (Internet), (108), p.11 - 17, 2019/11
Scintillators are generally used to detect various kinds of particles such as electrons, gammas, protons and heavy ions. Scintillators emit photons according to the energy deposited to the crystal. It is also known that light yield is suppressed for particles depositing energy densely owing to quenching. Moreover, it is suggested that quenching is attributed to transfer of energy from excited fluorescent molecules to damaged molecules (Frster mechanism or Dexter mechanism). In this study, energy deposition in a scintillator crystal by radiation was calculated using radiation transport codes to finally obtain excitation and damage of fluorescent molecules. Based on the calculation, spatial configuration of exited and damaged molecules. Then the probability that Frster mechanism takes place in excited molecules were estimated to obtain the number of fluorescent molecules that emit photons. As a result, light yield is proportionally increased with increase in the incident energy in case of electron incidence. On the other hand, light yield is increased non-linearly in case of proton incidence. This trend is in a good agreement with the experimental results.
Hoshasen (Internet), 45(2), p.77 - 88, 2019/07
JRR-3 operated by Japan Atomic Energy Agency (JAEA) is 20 MW grade research reactor for widely used for various academic research and industrial applications in many fields from utilization of internal irradiation to utilization of neutron beam. Although JRR-3 has not been operated due to respond to the new regulation standard established after the Great East Japan Earthquake of March 11, 2011, JRR-3 will resume operation in October 2020. This article reports neutron utilization such as various kinds of reactor irradiation, prompt gamma-ray analysis, neutron radiography and neutron residual stress analysis, and the efforts of the JRR-3 user 's office aiming for a one - stop office.
Hoshasen To Sangyo, (146), p.48 - 52, 2019/06
no abstracts in English
Hoshasen Kagaku (Internet), (107), p.77 - 78, 2019/04
Reaction of hydrogen peroxide (HO) with uranium dioxide (UO) oxidizes U(IV) to water-soluble U(VI). In the concept of direct geological disposal of spent nuclear fuel, this reaction is expected to induce dissolution of UO matrix of the spent fuel. This study investigate effect of HO concentration on the kinetics and the yield of U(VI) dissolution of this reaction. A series of experiments of the reaction of HO with UO powder dispersed in water has been carried out. The experimental results reveal that increase in the HO concentration slows down the reaction and decreases the yield of U(VI) dissolution. This observation suggests that a reaction intermediate is generated in the course of the HO reaction on the surface of UO.