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Journal Articles

Simulation study of a shield-free directional gamma-ray detector using Small-Angle Compton Scattering

Kitayama, Yoshiharu; Terasaka, Yuta; Sato, Yuki; Torii, Tatsuo

Journal of Nuclear Engineering and Radiation Science, 7(4), p.042006_1 - 042006_7, 2021/10

Journal Articles

Feasibility study of the one-dimensional radiation distribution sensing method using an optical fiber sensor based on wavelength spectrum unfolding

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 $$^{90}$$Sr/$$^{90}$$Y radioactive point source, basic properties of source position detection were confirmed.

Journal Articles

Ten years have passed since the accident of the Fukushima Daiichi Nuclear Power Plant; Current situation for the development for the new technology of radiation measurement and needs for decommissioning of the Fukushima Daiichi Nuclear Power Plant

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.

Journal Articles

Gamma-ray spectroscopy with a CeBr$$_3$$ scintillator under intense $$gamma$$-ray fields for nuclear decommissioning

Kaburagi, 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:1 Percentile:81.22(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$$_3$$ spectrometer with dimensions of 5 mm $$times$$ 5 mm $$times$$ 5 mm was manufactured to perform $$gamma$$-ray spectroscopy under intense $$gamma$$-ray fields. Furthermore, thanks to a fast digital process unit and a customized photomultiplier, the device could perform $$gamma$$-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 $$^{137}$$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 $$^{60}$$Co radiation field, which suggested to realize $$gamma$$-ray assessment of $$^{134}$$Cs, $$^{137}$$Cs, $$^{60}$$Co, and $$^{154}$$Eu at dose rates of over 1 Sv/h.

Journal Articles

Automatic data acquisition for visualizing radioactive substances by combining a gamma-ray imager and an autonomous mobile robot

Sato, Yuki; Minemoto, Kojiro*; Nemoto, Makoto*; Torii, Tatsuo

Journal of Instrumentation (Internet), 16(1), p.P01020_1 - P01020_18, 2021/01

 Times Cited Count:0 Percentile:0(Instruments & Instrumentation)

Journal Articles

Development of a Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$ (GPS) scintillator-based alpha imaging detector for rapid plutonium detection in high-radon environments

Morishita, 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:2 Percentile:62.87(Engineering, Electrical & Electronic)

We developed a Gd$$_{2}$$Si$$_{2}$$O$$_{7}$$ (GPS) scintillator-based alpha imaging detector and demonstrated its effectiveness by evaluating actual Pu particle and $$^{222}$$Rn progeny. The GPS scintillator plate was prepared by a sintering method. The outer dimensions of the GPS scintillator plate were 5 $$times$$ 5 cm, and the scintillator layer was approximately 50 $$mu$$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 ($$^{222}$$Rn) progeny counts were reduced by 65.3% by applying an energy window. Although the Pu/$$^{222}$$Rn progeny activity ratio was 1/51, the Pu particle was successfully identified among $$^{222}$$Rn progeny within the 5 min-measurement time. The imaging detector has an excellent ability for detecting Pu among $$^{222}$$Rn progeny. Thus, this detector is useful for alpha contamination monitoring in high-radon-background environments.

Journal Articles

Construction of virtual reality system for radiation working environment reproduced by gamma-ray imagers combined with SLAM technologies

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:6 Percentile:93.25(Instruments & Instrumentation)

Journal Articles

A Cubic CeBr$$_{3}$$ gamma-ray spectrometer suitable for the decommissioning of the Fukushima Daiichi Nuclear Power Station

Kaburagi, 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:3 Percentile:76.41(Instruments & Instrumentation)

Journal Articles

Retracted article; Visualization and integration of images of radioactive substances as point cloud data in 3-D environment models

Sato, Yuki; Torii, Tatsuo

Nuclear Technology, 206(7), p.v - xvi, 2020/07

 Times Cited Count:2 Percentile:62.87(Nuclear Science & Technology)

Journal Articles

Statement of retraction; Visualization and integration of images of radioactive substances as point cloud data in 3-D environment models

Sato, Yuki; Torii, Tatsuo

Nuclear Technology, 206(7), P. 1095, 2020/07

 Times Cited Count:0 Percentile:20(Nuclear Science & Technology)

Journal Articles

Remote detection of radioactive hotspot using a Compton camera mounted on a moving multi-copter drone above a contaminated area in Fukushima

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:7 Percentile:95.29(Nuclear Science & Technology)

Journal Articles

Evaluation of an ultra-thin plastic scintillator to detect alpha and beta particle contamination

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 $$^{90}$$Sr/$$^{90}$$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.

Journal Articles

Development of one-dimensional optical fiber type radiation distribution sensing method based on wavelength spectrum unfolding

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

Journal Articles

A Study of directional gamma-ray detector without shield by Monte Carlo simulation

Kitayama, Yoshiharu; Terasaka, Yuta; Sato, Yuki; Torii, Tatsuo

Proceedings of International Youth Nuclear Congress 2020 (IYNC 2020) (Internet), 4 Pages, 2020/05

Journal Articles

Visualization of radioactive substances using freely moving gamma-ray imager based on Structure from Motion

Sato, Yuki; Torii, Tatsuo

Proceedings of International Youth Nuclear Congress 2020 (IYNC 2020) (Internet), 4 Pages, 2020/05

Journal Articles

A Remote continuous air monitoring system for measuring airborne alpha contamination

Morishita, Yuki; Usami, Hiroshi; Furuta, Yoshihiro; Aoki, Katsunori; Tsurudome, Koji; Hoshi, Katsuya; Torii, Tatsuo

Radiation Protection Dosimetry, 189(2), p.172 - 181, 2020/04

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

We developed a remote continuous air monitoring (RCAM) system. The RCAM system consisted of a personal air monitor and a robot. The personal air monitor (poCAMon, SARAD, Germany) had a 400 mm$$^{2}$$ ion-injected silicon detector and a membrane air filter with 25 mm-diameter. The personal air monitor provides the alpha energy spectra for any measurement time interval. Demonstration measurements were taken underground at the Mizunami Underground Research Laboratory (MIU) and at a poorly ventilated concrete building. The RCAM system was remotely operated and successfully measured the $$^{222}$$Rn progeny even though the relative humidity (RH) was almost 100%. In the measured alpha spectra, the peaks of $$^{218}$$Po (6.0 MeV alpha) and $$^{214}$$Po (7.7 MeV alpha) were clearly identified. Our developed monitor is promising for alpha dust monitoring in a high gamma-ray environment or contaminated areas where a worker cannot safely physically enter.

JAEA Reports

RADREMOTE 2018; Proceedings of The 5th Fukushima Research Conference (FRC) 2018; Radiation hardness, smartness and measurement in remote technology for the decommissioning of the Fukushima Daiichi Nuclear Power Station

Kaburagi, Masaaki; Torii, Tatsuo; Ogawa, Toru

JAEA-Review 2019-031, 251 Pages, 2020/01

JAEA-Review-2019-031.pdf:57.36MB

There is high expectation for advanced remote technology and robotics to reduce the radiation exposure for workers in harsh nuclear environments such as the decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS). However, the radiation tolerance of state-of-the-art key components, sensors and electronic devices, for remote operation is still limited. In order to extend the application of robotics in nuclear energy, it is pertinent to develop "Radiation hardness" of components and "Radiation smartness" in operation procedures. Furthermore, developments of "Radiation measurement" and "Technology to recognize the location and to grasp the surrounding environment", including the radiation imaging of the high dose-rate fields inside the FDNPS and the detection of nuclear fuel debris, are necessary for the future nuclear fuel debris retrieval. This Fukushima Research Conference aims to share the future vision for advancing the remote technology among experts from diverse fields.

Journal Articles

Detection of alpha emitters originating from Fukushima Daiichi Power Station using an alpha imaging detector

Morishita, Yuki; Usami, Hiroshi; Torii, Tatsuo

Isotope News, (765), p.10 - 13, 2019/10

This paper reports the development of an alpha particle imaging detector to detect alpha emitters originating from the Fukushima Daiichi Nuclear Power Station and the actual measurement of smear papers.

Journal Articles

Radiation imaging using a compact Compton camera mounted on a crawler robot inside reactor buildings of Fukushima Daiichi Nuclear Power Station

Sato, Yuki; Terasaka, Yuta; Utsugi, Wataru*; Kikuchi, Hiroyuki*; Kiyooka, Hideo*; Torii, Tatsuo

Journal of Nuclear Science and Technology, 56(9-10), p.801 - 808, 2019/09

 Times Cited Count:18 Percentile:97.74(Nuclear Science & Technology)

243 (Records 1-20 displayed on this page)