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Torii, Tatsuo; Sanada, Yukihisa
Introduction to Environmental Radioactivity, p.31 - 54, 2024/02
no abstracts in English
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.
Torii, Tatsuo; Sanada, Yukihisa
Keisoku Gijutsu, 50(11), p.23 - 28, 2022/10
no abstracts in English
Torii, Tatsuo*; Sanada, Yukihisa; Sato, Yuki
Nihon Genshiryoku Gakkai-Shi ATOMO
, 64(1), p.17 - 22, 2022/01
Ten years have passed since the accident at the Fukushima Daiichi Nuclear Power Station. Due to the accident, radioactive materials were widely diffused and deposited not only in the building and site of the Fukushima Daiichi Nuclear Power Station but also in the environment. Demand has increased, and the introduction and development of radiation imaging equipment called gamma cameras and mapping of radiation distribution in the environment have been promoted. Here, we will introduce the radiation distribution measurement technology that has been developed and operated after the accident, and describe the future prospects.
Torii, Tatsuo*; Sanada, Yukihisa
Behavior of Radionuclides in the Environment III; Fukushima, p.17 - 29, 2022/00
Airborne radiation survey was conducted to evaluate the influence of radionuclides emitted by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Carrying out airborne radiation surveys using a manned helicopter, the Japan Atomic Energy Agency (JAEA) has developed and established an analysis method concurrently with the development of this survey method. In particular, because the background radiation level differs greatly between the East and West regions of Japan, the JAEA has developed a discrimination method for natural radionuclide and cosmic rays using the gamma energy spectra. The reliability of the airborne radiation monitoring data was confirmed through comparison with large amounts of ground measurement data. Here, we report on the measurement technique and the results. The ambient dose rate has been decreased by the increasing attenuation effect due to radioactive cesium penetration into the soil in addition to the physical decay of radioactive cesium. These results indicate the importance of airborne monitoring to evaluate and predict the radiation exposure of residents.
Sato, Yuki; Minemoto, Kojiro*; Nemoto, Makoto*; Torii, Tatsuo
Journal of Nuclear Engineering and Radiation Science, 7(4), p.042003_1 - 042003_12, 2021/10
Kitayama, Yoshiharu; Terasaka, Yuta; Sato, Yuki; Torii, Tatsuo
Journal of Nuclear Engineering and Radiation Science, 7(4), p.042006_1 - 042006_7, 2021/10
Terasaka, Yuta; Watanabe, Kenichi*; Uritani, Akira*; Yamazaki, Atsushi*; Sato, Yuki; Torii, Tatsuo; Wakaida, Ikuo
Journal of Nuclear Engineering and Radiation Science, 7(4), p.042002_1 - 042002_7, 2021/10
For the application in the measurement of the high dose rate hot spots inside the Fukushima Daiichi Nuclear Power Station (FDNPS) buildings, we propose a novel one-dimensional radiation distribution sensing method using an optical fiber sensor based on wavelength spectrum unfolding. The proposed method estimates the incident position of radiation to the fiber by the unfolding of the wavelength spectrum output from the fiber edge using the fact that the attenuation length of light along the fiber depends on the wavelength. Because this method measures the integrated light intensity, this method can avoid the problem of counting loss and signal pile-up, which occurs in the radiation detector with pulse counting mode under high dose rate field. Through basic experiments using the ultraviolet light source and 
Sr/Y radioactive point source, basic properties of source position detection were confirmed.
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.
scintillator under intense 
-ray fields for nuclear decommissioningKaburagi, Masaaki; Shimazoe, Kenji*; Kato, Masahiro*; Kurosawa, Tadahiro*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.
Nuclear Instruments and Methods in Physics Research A, 988, p.164900_1 - 164900_8, 2021/02
Times Cited Count：11 Percentile：89.29(Instruments & Instrumentation)An increasing number of nuclear facilities have been decommissioned worldwide following the 2011 accident of the TEPCO' Fukushima Daiichi Nuclear Power Station. During the decommissioning, radioactive materials have to be retrieved under proper management. In this study, a small cubic CeBr spectrometer with dimensions of 5 mm 
5 mm 5 mm was manufactured to perform -ray spectroscopy under intense -ray fields. Furthermore, thanks to a fast digital process unit and a customized photomultiplier, the device could perform -ray spectroscopy at dose rates of over 1 Sv/h. The energy resolution (FWHM) at 662 keV ranged from 4.4% at 22 mSv/h to 5.2% at 1407 mSv/h for a 
Cs radiation field. Correspondingly, at 1333 keV, it ranged from 3.1% at 26 mSv/h to 4.2% at 2221 mSv/h for a 
Co radiation field, which suggested to realize -ray assessment of 
Cs, Cs, Co, and 
Eu at dose rates of over 1 Sv/h.
Sato, Yuki; Minemoto, Kojiro*; Nemoto, Makoto*; Torii, Tatsuo
Journal of Instrumentation (Internet), 16(1), p.P01020_1 - P01020_18, 2021/01
Times Cited Count：1 Percentile：9.32(Instruments & Instrumentation)Sato, Yuki; Terasaka, Yuta; Torii, Tatsuo
Nihon Genshiryoku Gakkai-Shi ATOMO, 62(11), p.645 - 649, 2020/11
no abstracts in English
SiO
(GPS) scintillator-based alpha imaging detector for rapid plutonium detection in high-radon environmentsMorishita, Yuki; Izaki, Kenji; Kaneko, Junichi*; Yamamoto, Seiichi*; Higuchi, Mikio*; Torii, Tatsuo
IEEE Transactions on Nuclear Science, 67(10), p.2203 - 2208, 2020/10
Times Cited Count：9 Percentile：71.58(Engineering, Electrical & Electronic)We developed a GdSiO (GPS) scintillator-based alpha imaging detector and demonstrated its effectiveness by evaluating actual Pu particle and 
Rn progeny. The GPS scintillator plate was prepared by a sintering method. The outer dimensions of the GPS scintillator plate were 5 5 cm, and the scintillator layer was approximately 50 
m on a 3-mm-thick high-transparency glass. The plate was optically coupled to a position-sensitive photomultiplier tube with silicone grease. The developed imaging detector exhibited good uniformity. Pu particle activities were accurately evaluated at 14 different positions, and the difference in activity was within 6%. Radon-222 (Rn) progeny counts were reduced by 65.3% by applying an energy window. Although the Pu/Rn progeny activity ratio was 1/51, the Pu particle was successfully identified among Rn progeny within the 5 min-measurement time. The imaging detector has an excellent ability for detecting Pu among Rn progeny. Thus, this detector is useful for alpha contamination monitoring in high-radon-background environments.
Sato, Yuki; Minemoto, Kojiro*; Nemoto, Makoto*; Torii, Tatsuo
Nuclear Instruments and Methods in Physics Research A, 976, p.164286_1 - 164286_6, 2020/10
Times Cited Count：14 Percentile：87.95(Instruments & Instrumentation)
gamma-ray spectrometer suitable for the decommissioning of the Fukushima Daiichi Nuclear Power StationKaburagi, Masaaki; Shimazoe, Kenji*; Otaka, Yutaka*; Uenomachi, Mizuki*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.
Nuclear Instruments and Methods in Physics Research A, 971, p.164118_1 - 164118_8, 2020/08
Times Cited Count：7 Percentile：66.68(Instruments & Instrumentation)Sato, Yuki; Torii, Tatsuo
Nuclear Technology, 206(7), p.v - xvi, 2020/07
Times Cited Count：2 Percentile：24.28(Nuclear Science & Technology)Sato, Yuki; Torii, Tatsuo
Nuclear Technology, 206(7), P. 1095, 2020/07
Times Cited Count：0 Percentile：20(Nuclear Science & Technology)Sato, Yuki; Ozawa, Shingo*; Terasaka, Yuta; Minemoto, Kojiro*; Tamura, Satoshi*; Shingu, Kazutoshi*; Nemoto, Makoto*; Torii, Tatsuo
Journal of Nuclear Science and Technology, 57(6), p.734 - 744, 2020/06
Times Cited Count：20 Percentile：93.76(Nuclear Science & Technology)Morishita, Yuki; Hoshi, Katsuya; Torii, Tatsuo
Nuclear Instruments and Methods in Physics Research A, 966, p.163795_1 - 163795_8, 2020/06
To date, alpha and high beta particle emitters have been detected in the reactor buildings of the Fukushima Daiichi Nuclear Power Station (FDNPS). Since the beta radiation levels in the FDNPS buildings are extremely high, a commercial beta survey meter, such as a Geiger-Muller (GM) counter, would no longer have the ability to measure the beta contamination levels. In order to solve this issue, we utilized ultra-thin plastic scintillators to increase the detection rate of alpha and beta contamination. In this study, ultra-thin plastic scintillators with varied thicknesses of 7, 22, 24, 31, 39, and 55 um were prepared. To test their sensitivity, each scintillator was optically coupled to a glass plate and a 2-in square position-sensitive photomultiplier tube, and exposed to either an alpha, beta, or gamma source. Results from alpha spectrometry show that only the 55 um-thick plastic scintillator fully absorbed the alpha particles (5.5 MeV) with a 16.7% Full Width at Half Maximum. For alpha imaging under a high beta background, the 7 um-thick plastic scintillator was found to be the best choice, with an alpha to beta ratio of 652. This plastic scintillator also had the lowest sensitivity to beta particles, measuring only 41.74 cps when exposed to a 1 MBq Sr/Y source in contact. It would therefore be possible to use the 7 um-thick plastic scintillator, to directly measure the surface contamination levels at the FDNPS site in real-time, where previous methods have fallen short. Thus, the developed detector would be a useful tool for the detection of alpha and beta contamination in the FDNPS.
Terasaka, Yuta; Watanabe, Kenichi*; Uritani, Akira*; Yamazaki, Atsushi*; Sato, Yuki; Torii, Tatsuo; Wakaida, Ikuo
Proceedings of International Youth Nuclear Congress 2020 (IYNC 2020) (Internet), 4 Pages, 2020/05
