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Kimura, Yoshiki; Yamaguchi, Tomoki
Radioisotopes, 74(3), p.251 - 264, 2025/11
Radioisotope identification (RIID) by gamma-ray spectral analysis has been widely used, and accurate identification of radioisotopes is an important issue in various fields. Handheld instruments are commonly used for on-site RIID but often suffer from limited performance. This paper proposes a spectral deconvolution using unsupervised neural network models for RIID with handheld instruments in field use. This approach allows optimization of the neural network for deconvolution based on a measured spectrum combined with an energy-broadening matrix, and it does not require extensive training datasets or the precise modeling of the detector and measurement conditions. The performance of the proposed approach was examined in simulated and measured spectra, assuming the measurements of several radioisotopes with CsI(Tl) spectrometers. It was demonstrated that the unsupervised neural network models can improve the peak resolution more significantly compared to conventional deconvolution algorithms and contribute to RIID performance in the low energy resolution spectra.
Kimura, Yoshiki; Yamaguchi, Tomoki
Progress in Nuclear Science and Technology (Internet), 7, p.60 - 66, 2025/03
Kimura, Yoshiki; Matsumoto, Tetsuya*; Yamaguchi, Tomoki
Dai-45-Kai Nihon Kaku Busshitsu Kanri Gakkai Nenji Taikai Kaigi Rombunshu (Internet), 4 Pages, 2024/11
no abstracts in English
Kimura, Yoshiki; Matsumoto, Tetsuya*; Yamaguchi, Tomoki
Journal of Radioanalytical and Nuclear Chemistry, 333(7), p.3541 - 3551, 2024/07
Times Cited Count：1 Percentile：20.46(Chemistry, Analytical)Machida, Masahiko; Yamada, Susumu; Kim, M.; Okumura, Masahiko; Miyamura, Hiroko; Shikaze, Yoshiaki; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; Yamaguchi, Takashi; et al.
RIST News, (69), p.2 - 18, 2023/09
The contamination of radioactive materials leaked from the reactor has resulted in numerous hot spots in the Fukushima Daiichi Nuclear Power Station (1F) building, posing obstacles to its decommissioning. In order to solve this problem, JAEA has conducted research and development of the digital technique for inverse estimation of radiation source distribution and countermeasures against the estimated source in virtual space for two years from 2021 based on the subsidy program "Project of Decommissioning and Contaminated Water Management" performed by the funds from the Ministry of Economy, Trade and Industry. In this article, we introduce the results of the project and the plan of the renewal project started in April 2023. For the former project, we report the derivative method for LASSO method considering the complex structure inside the building and the character of the source and show the result of the inverse estimation using the method in the real reactor building. Moreover, we explain the platform software "3D-ADRES-Indoor" which integrates these achievements. Finally, we introduce the plan of the latter project.
Yamamoto, Masahiko; Kono, Soma; Saegusa, Yu; Kuno, Takehiko; Sekine, Megumi; Inoue, Naoko; Noro, Naoko; Rodriguez, D. C.; Yamaguchi, Tomoki; Stinett, J.*
Proceedings of INMM & ESARDA Joint Annual Meeting 2023 (Internet), 10 Pages, 2023/05
The gamma-ray measurement part of the Non-Destructive Assay (NDA) course of safeguards and nuclear material accountancy was developed to focus on gamma-ray measurement allotting two days out of five days. The lectures on the basic characteristics and detection methods and mechanism of gamma-ray detectors were provided as e-learnings which were developed. The part for hands-on exercises were implemented in JAEA facility. Participants have set up each gamma-ray detector, and performed measurements of uranium and the other gamma-ray emitting nuclides. Also, uranium-235 enrichment measurements have been performed. In addition, the participants trained with a handheld gamma-ray spectrometer, HM-5, that is popular for IAEA safeguards as the preparation in the measurement exercise of fresh fuel assemblies in JRR-3, a research reactor facility of JAEA. This paper reports on the development, implementation, and feedback from participants on gamma-ray measurement part of the NDA course.
Machida, Masahiko; Yamada, Susumu; Kim, M.; Okumura, Masahiko; Miyamura, Hiroko; Malins, A.; Shikaze, Yoshiaki; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; et al.
RIST News, (68), p.3 - 19, 2022/09
no abstracts in English
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count：66 Percentile：94.76(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 
C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Shiba, Tomooki; Tomikawa, Hirofumi; Yamaguchi, Tomoki
Dai-41-Kai Nihon Kaku Busshitsu Kanri Gakkai Nenji Taikai Kaigi Rombunshu (Internet), 4 Pages, 2020/11
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.
Science, 364(6437), p.272 - 275, 2019/04
Times Cited Count：329 Percentile：99.61(Multidisciplinary Sciences)The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
Nishimura, Katsuhiko*; Matsuda, Kenji*; Lee, S.*; Nunomura, Norio*; Shimano, Tomoki*; Bendo, A.*; Watanabe, Katsumi*; Tsuchiya, Taiki*; Namiki, Takahiro*; Toda, Hiroyuki*; et al.
Journal of Alloys and Compounds, 774, p.405 - 409, 2019/02
Times Cited Count：4 Percentile：16.51(Chemistry, Physical)Matsuoka, Moe*; Nakamura, Tomoki*; Osawa, Takahito; Iwata, Takahiro*; Kitazato, Kohei*; Abe, Masanao*; Nakauchi, Yusuke*; Arai, Takehiko*; Komatsu, Mutsumi*; Hiroi, Takahiro*; et al.
Earth, Planets and Space (Internet), 69(1), p.120_1 - 120_12, 2017/12
Times Cited Count：6 Percentile：16.49(Geosciences, Multidisciplinary)We have conducted ground-based performance evaluation tests of the Near-Infrared Spectrometer (NIRS3) onboard Hayabusa2 spacecraft and established a method for evaluating its measured reflectance spectra. Reflectance spectra of nine powdered carbonaceous chondrite samples were measured by both NIRS3 and a FT-IR spectrometer. Since raw data obtained by NIRS3 had considerable spectral distortion caused by systematic offsets in sensitivity of individual pixels, we have established two methods for correcting the NIRS3 data by comparing them with the corresponding FT-IR data. In order to characterize the absorption bands in NIRS3 spectra, the depth of each band component D
is defined for each wavelength (
m). Reflectance spectra of asteroid Ryugu, the target asteroid of Hayabusa2, to be recorded by the NIRS3 are expected to reveal the characteristics of the surface materials by using the evaluation technique.
Saigusa, Mikio*; Atsumi, Kohei*; Yamaguchi, Tomoki*; Oda, Yasuhisa; Sakamoto, Keishi
Fusion Engineering and Design, 88(6-8), p.964 - 969, 2013/10
Times Cited Count：2 Percentile：16.58(Nuclear Science & Technology)Atsumi, Kohei*; Yamaguchi, Tomoki*; Nagashima, Koji*; Saigusa, Mikio*; Fukunari, Masafumi*; Oda, Yasuhisa; Sakamoto, Keishi
Plasma and Fusion Research (Internet), 8(Sp.1), p.2405077_1 - 2405077_4, 2013/06
Matsui, Yoshiki; Kimura, Yoshiki; Umino, Yuji*; Hosoi, Masaharu*; Matsumoto, Tetsuya*; Shinohara, Nobuo; Yamazaki, Hitoshi; Yamaguchi, Tomoki
no journal, ,
Takii, Keita*; Yamaguchi, Tomoki*; Nagashima, Koji*; Sekiguchi, Kenji*; Saigusa, Mikio*; Oda, Yasuhisa; Fukunari, Masafumi*; Sakamoto, Keishi
no journal, ,
no abstracts in English
Takir, D.*; Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; et al.
no journal, ,
JAXA spacecraft and sample return mission Hayabusa2 has arrived at the near-Earth asteroid 162173 Ryugu, which is classified a primitive carbonaceous object. Here we report recent results of near-infrared spectrometer (NIRS3) on the Hayabusa2 spacecraft. The observations provide direct measurements of the surface composition of Ryugu and context for the returned samples. NIRS3 has detected a weak and narrow absorption feature centered at 2.72 micrometer across entire observed surface. This absorption feature is attributed to the presence of OH-bearing minerals. The NIRS3 observations also revealed that Ryugu is the darkest object to be observed up-close by a visiting spacecraft. The intensity of the OH feature and low albedo are consistent with thermally-and/or shock-metamorphosed, and/or carbon-rich space-weathered primitive and hydrated carbonaceous chondrites.
Nagashima, Koji*; Yamaguchi, Tomoki*; Takii, Keita*; Sekiguchi, Kenji*; Saigusa, Mikio*; Oda, Yasuhisa; Fukunari, Masafumi*; Sakamoto, Keishi
no journal, ,
no abstracts in English
Yamaguchi, Tomoki*; Atsumi, Kohei*; Nagashima, Koji*; Saigusa, Mikio*; Oda, Yasuhisa; Fukunari, Masafumi*; Sakamoto, Keishi
no journal, ,
no abstracts in English
Saigusa, Mikio*; Sugawara, Shuhei*; Atsumi, Kohei*; Oda, Yasuhisa; Yamaguchi, Tomoki*; Sakamoto, Keishi
no journal, ,
