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Journal Articles

An Experimental feasibility study of a 4$$pi$$ gamma-ray imager using detector response patterns

Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*

Japanese Journal of Applied Physics, 63(7), p.076502_1 - 076502_8, 2024/07

 Times Cited Count:0 Percentile:0.00(Physics, Applied)

We constructed a gamma-ray imager that estimates the distribution of gamma-ray sources based on the response patterns of multiple gamma-ray detectors randomly positioned in three-dimensional space. The Coded Cube Camera for Gamma-ray (C3G), comprising eight GAGG (Ce) scintillator and eighteen lead cubes is housed in a cubical casing with an 86 mm edge length and weighs approximately 600 g. Results of the 4$$pi$$ imaging experiment confirmed the feasibility of imaging a 10 MBq $$^{137}$$Cs source located 3 m away with an angular uncertainty of 5$$^{circ}$$ within a 10 min measurement. C3G operates with only eight channels, instead of the hundreds needed by a typical imager, offering a simplified circuit and reconstruction algorithm, thereby achieving a cost-effective and reliable system. With its compact and lightweight design, 4$$pi$$ field of view, and high angular uncertainty, this technology is expected to find extensive applications in astronomy, medicine, nuclear security, and decommissioning projects.

Journal Articles

Novel 4$$pi$$ field-of-view gamma-ray imaging

Kitayama, Yoshiharu

IEEE NPSS Newsletter (Internet), 4 Pages, 2024/06

Journal Articles

Development of radiation measurement and digital technologies for the decommissioning of the Fukushima Daiichi Nuclear Power Plant

Takasaki, Koji

Hokeikyo Nyusu, (73), p.2 - 5, 2024/04

The development of radiation measurement and digital technology for the decommissioning of the Fukushima Daiichi Nuclear Power Plant, which is being conducted by the Remote System and Sensing Technology Division of CLADS, will be presented.

Journal Articles

Simulation of a gamma-ray imaging technique using detector response patterns

Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*

Japanese Journal of Applied Physics, 63(3), p.032005_1 - 032005_6, 2024/03

 Times Cited Count:1 Percentile:35.22(Physics, Applied)

We introduce a novel gamma-ray imaging technique that uses detector response patterns. This method employs multiple shielding cubes randomly positioned in a three-dimensional configuration. Within the volume defined by these cubes, a unique gamma-ray flux pattern is formed based on the incidence direction of the gamma rays. This pattern can be measured using the responses of several scintillator cubes. By pre-measuring the detector response pattern and incidence direction of the gamma rays, the incidence direction can be estimated using an unfolding technique. Simulations were performed using a $$^{137}$$Cs point source. Our results show that a 10 MBq $$^{137}$$Cs source, located 3 m away from the imager, can be imaged with an angular resolution close to 10$$^{circ}$$. These findings suggest that our new method is comparable to existing gamma-ray imaging techniques. Potential applications of this imaging method include nuclear power plant decommissioning, nuclear medicine, security, and astronomy.

Journal Articles

Application of machine learning to spattering phenomena in laser cutting

Kusumoto, Toshiyuki*; Saruta, Koichi; Naoe, Takashi; Teshigawara, Makoto; Futakawa, Masatoshi; Hasegawa, Kazuo*; Tsuboi, Akihiko

Jikken Rikigaku, 23(4), p.310 - 315, 2023/12

Reducing spatter, i.e., melt droplets flown out of the melt pool, is one of the critical issues when laser cutting is employed as a machining tool for radioactive wastes because the ejected droplets can lead to radioactive contamination with potential human exposure. The spattering phenomena are complicated processes that involve multiple physical phenomena, causing difficulty in the determination of laser parameters to minimize the amount of spatter. Here we observe the spatter ejected from 316L stainless steel plates using a high-speed camera and apply a machine learning technique to these captured images on the basis of three distinctive behaviors appeared at specific time intervals of the process of spattering phenomena: (I) a vapor, (II) a liquid film and breakup into droplets, and (III) a liquid capillary. The numerical model established through the machine learning technique predicts the spattering phenomena with an accuracy of 89% and can be used to determine the laser power and beam diameter that reduce the spatter eruption during laser irradiation.

Journal Articles

Demonstration of radioactive contamination visualization using the integrated Radiation Imaging System; iRIS

Sato, Yuki

Chino To Joho, 35(4), p.81 - 86, 2023/11

no abstracts in English

Journal Articles

Compton camera measurements of radiation distribution images at Hamadori, Fukushima Prefecture

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.

Journal Articles

Fundamental research of X-ray absorption imaging for elemental identification using a secondary target

Nakae, Masanori*; Matsuyama, Tsugufumi*; Murakami, Masashi; Yoshida, Yukihiko; Machida, Masahiko; Tsuji, Koichi*

Advances in X-Ray Chemical Analysis, Japan, 54, p.89 - 99, 2023/03

Fundamental research on X-ray absorption imaging for elemental identification was studied. A secondary target was applied to obtain X-ray absorption images above and below the X-ray absorption edge of the target element. X-rays from an X-ray tube were irradiated to the secondary target, where the characteristic X-rays were emitted that were irradiated to the sample. X-ray absorption images were acquired with an exposure time of a few seconds with an X-ray camera. In this technique, it is difficult to change the energy of X-rays as we want, however we can apply this technique for imaging the specific element. Metal foil sample composed of Al, Cu, and Ni was analyzed. To obtain an X-ray elemental image of Ni, two X-ray absorption images were taken using the X-rays above and below the Ni K-edge. X-rays of Cu K$$alpha$$ and Zn K$$alpha$$ were prepared by using Cu and Zn plates as the secondary target. Finally, the Ni elemental image was obtained by subtracting two images. Furthermore, the X-ray camera had a function of setting critical energies for imaging, thus it was demonstrated that an X-ray elemental image of Ni was obtained using a single secondary target without changing the secondary target.

Journal Articles

Gamma-ray imaging using three-dimensional shadow images created by coded solid

Kitayama, Yoshiharu; Nogami, Mitsuhiro*; Hitomi, Keitaro*

KEK Proceedings 2022-3, p.46 - 53, 2023/01

The position of a streetlight can be predicted from the direction and shape of one's shadow projected on the street at night by the light of the streetlight. The application of this idea to gamma-ray imagers is known as coded aperture. In this study, we proposed the Coded Cube Camera - POrtable (C3PO), which has a three-dimensional shielding and scintillator crystal arrangement, and is composed of lead, scintillator, and depletion cubes randomly arranged in a 3$$times$$3$$times$$3 Rurik's cube shape, with each. The output of each scintillator produces a three-dimensional shadow pattern, which is returned to the source direction distribution by unfolding. In this study, we investigated the characteristics and feasibility of the system by simulation using Geant 4.

Journal Articles

3D visualization of radioactive contamination using an integrated Radiation Imaging System (iRIS)

Sato, Yuki

Isotope News, (781), p.19 - 23, 2022/06

no abstracts in English

Journal Articles

Development of an integrated Radiation Imaging System

Sato, Yuki

Kensa Gijutsu, 27(5), p.9 - 15, 2022/05

no abstracts in English

Journal Articles

Improvement of analysis results from the GAGG scintillator Compton camera operated on an unmanned helicopter by selecting stable flight conditions

Shikaze, Yoshiaki; Shimazoe, Kenji*

Journal of Nuclear Science and Technology, 59(1), p.44 - 54, 2022/01

 Times Cited Count:4 Percentile:39.96(Nuclear Science & Technology)

A Compton camera system for use on an unmanned helicopter was previously developed for characterizing the distribution of radioactive materials in highly contaminated areas. For this study, a small camera, a laser distance meter, an attitude angles sensor, temperature sensors, and real-time monitoring software were equipped to the Compton camera system to better measure flight parameters and to more precisely detect hot spot locations. To confirm if detection results were improved by the modifications, measurements were taken from hovering and programmed flights over a field in Okuma, Fukushima Prefecture (Japan). Ambient dose equivalent rate distributions at ground level were obtained by processing the flight data, then compared against measurements taken at ground level on foot using a survey meter. For one hovering flight, the correlation between the datasets was improved by selecting a period of stable flight position and attitude, and by restricting the deviation of the attitude angles. Between 6.0%-7.6% improvement in the position resolution was achieved by using the data from stable flight periods, even when using 1 minute data windows. The precision of hot spot detections and ambient dose equivalent rate distributions obtained from the Compton camera were thus improved by the aforementioned modifications to the system.

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:3 Percentile:40.00(Nuclear Science & Technology)

Journal Articles

A Radiation hardened CMOS image sensor with almost zero dark current increase during radiation

Watanabe, Takashi*; Takeuchi, Tomoaki; Ozawa, Osamu*; Komanome, Hirohisa*; Akahori, Tomoyuki*; Tsuchiya, Kunihiko

Proceedings of 2019 International Image Sensor Workshop (IISW 2019) (Internet), 4 Pages, 2019/06

Radiation hard image sensors have been developed past decades among the world. Almost papers discussed properties before and after radiation but images during radiation were not described yet. We have developed a new type of rad-hard pixel and integrated to 1.3M-pixel, 18-bit digital CMOS image sensor. Pixel area consists of several types of variation and the sensor has been analyzed during gamma ray radiation higher than 1 kGy/h up to 200 kGy. As the result, one type of pixel showed almost zero dark current increase at whole period.

Journal Articles

Development of radiation resistant monitoring system in light water reactor

Takeuchi, Tomoaki; Otsuka, Noriaki; Nakano, Hiroko; Iida, Tatsuya*; Ozawa, Osamu*; Shibagaki, Taro*; Komanome, Hirohisa*; Tsuchiya, Kunihiko

QST-M-16; QST Takasaki Annual Report 2017, P. 67, 2019/03

no abstracts in English

Journal Articles

Challenge of decommissioning of Fukushima I Nuclear Power Plant, 4; Development of radiation resistant image sensor

Watanabe, Takashi*; Ozawa, Osamu*; Takeuchi, Tomoaki

Denki Gakkai-Shi, 138(8), p.529 - 534, 2018/08

no abstracts in English

Journal Articles

A Three-dimensional imaging technique for radioactive contamination

Sato, Yuki; Torii, Tatsuo

Isotope News, (757), p.44 - 47, 2018/06

no abstracts in English

Journal Articles

A New radiation hardened CMOS image sensor for nuclear plant

Watanabe, Takashi*; Takeuchi, Tomoaki; Ozawa, Osamu*; Komanome, Hirohisa*; Akahori, Tomoyuki*; Tsuchiya, Kunihiko

Proceedings of 2017 International Image Sensor Workshop (IISW 2017) (Internet), p.206 - 209, 2017/05

no abstracts in English

140 (Records 1-20 displayed on this page)