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論文

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

北山 佳治; 寺阪 祐太; 佐藤 優樹; 鳥居 建男

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

Gamma-ray imaging is a technique to visualize the spatial distribution of radioactive materials. Recently, gamma-ray imaging has been applied to research on decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS) accident and environmental restoration, and active research has been conducted. This study is the elemental technology study of the new gamma-ray imager GISAS (Gamma-ray Imager using Small-Angle Scattering), which is assumed to be applied to the decommissioning site of FDNPS. GISAS consists of a set of directional gamma-ray detectors that do not require a shield. In this study, we investigated the feasibility of the shield free directional gamma-ray detector by simulation. The simulation result suggests that by measuring several keV of scattered electron energy by scatterer detector, gamma rays with ultra-small angle scattering could be selected. By using Compton scattering kinematics, a shield-free detector with directivity of about 10$$^{circ}$$ could be feasible. By arranging the directional gamma-ray detectors in an array, it is expected to realize the GISAS, which is small, light, and capable of quantitative measurement.

論文

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

寺阪 祐太; 渡辺 賢一*; 瓜谷 章*; 山崎 淳*; 佐藤 優樹; 鳥居 建男; 若井田 育夫

Journal of Nuclear Engineering and Radiation Science, 7(4), p.042002_1 - 042002_7, 2021/10

福島第一原子力発電所原子炉建物内の高線量率環境での線源分布測定への応用を目指し、波長スペクトルのアンフォールディング処理に基づく光ファイバーを用いた新しい一次元放射線分布測定法を開発した。開発した手法は光ファイバー内を伝搬する光の減衰量が波長依存であることを利用して、光ファイバー端から出力された波長スペクトルをアンフォールディングすることにより、光ファイバーへの放射線の入射位置を逆推定するというものである。この手法は光強度の積分値を利用するため、パルスカウンティングを行う放射線検出器を使用した場合に高線量率環境下で発生する計数損失や信号パイルアップの問題を回避することができる。本研究では紫外光源と90Sr/90Y放射線源を用いた基礎実験を行い、線源位置検出の基本特性を確認した。

論文

3D position and radioactivity estimation of radiation source by a simple directional radiation detector combined with structure from motion

佐藤 優樹; 峯本 浩二郎*; 根本 誠*

Radiation Measurements, 142, p.106557_1 - 106557_6, 2021/03

 被引用回数:0 パーセンタイル:0.02(Nuclear Science & Technology)

It is important to visualize radioactive substances' position and distribution and estimate their radioactivity levels to reduce the exposure dose of workers in radioactive areas (such as decommissioning worksites of nuclear power stations) and improve nuclear security functions. To visualize the radioactive substance's three-dimensional (3D) location, a directional radiation detector with a cylindrical shield on a simple single-pixel gamma-ray detector was applied to the structure from motion (SfM) technology using an ordinary digital camera. Verification was performed by a system that combines SfM with a CdTe sensor probe having narrow directivity. $$^{241}$$Am radiation source's position was visualized by drawing the radiation source's image acquired by the gamma-ray detector on the work area 3D model reconstructed through SfM. Furthermore, as SfM is a simultaneous localization and mapping technology, the system measures the gamma rays while measuring the gamma-ray detector's dynamic position and posture information. The measurements can be acquired while the gamma-ray detector is freely moving in the work area. These methods visualized the radiation source's position and quantitatively estimated the radiation source's radioactivity.

論文

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

佐藤 優樹; 峯本 浩二郎*; 根本 誠*; 鳥居 建男

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

 被引用回数:0 パーセンタイル:0.01(Instruments & Instrumentation)

To reduce the exposure doses of workers and to establish decontamination plans, it is important to understand and visualize the distribution of radioactive substances at the Fukushima Daiichi Nuclear Power Station in Japan, where an accident occurred on the 11th of March, 2011. In this decommissioning work environment, radioactive substances adhered to various objects, such as rubble and equipment, and it was necessary to visualize the distribution of these contaminants in all three dimensions. The technology used to automatically and remotely acquire data to visualize the distribution of radioactive substances in three dimensions was useful for reducing the exposure dose of the workers and to shorten the survey time. We constructed an automatic data acquisition system that consisted of a Compton camera and a 3D-light detection and ranging sensor mounted on an autonomously moving robot. We also evaluated the system feasibility using radiation sources and succeeded in automatically acquiring the data required for visualizing the radiation sources. For this data acquisition, the operator did not need to operate the system after the measurements were started. The effects of the imaging parameters of the Compton camera and the accuracy of the self-position estimation of the system on the radiation-imaging accuracy are also discussed.

論文

福島第一原子力発電所廃炉作業環境における遠隔放射線イメージング技術の開発と実証; 統合型放射線イメージングシステムiRISの構築

佐藤 優樹; 寺阪 祐太; 鳥居 建男

日本原子力学会誌ATOMO$$Sigma$$, 62(11), p.645 - 649, 2020/11

東京電力ホールディングス福島第一原子力発電所の廃炉作業を円滑に進めるにあたり、作業環境に飛散・沈着した放射性物質の分布を「見える化」して把握することは、作業者の被ばく線量の低減や詳細な作業計画の立案を行う上で重要である。ここではわれわれが福島第一原子力発電所やその周辺で行なってきた放射線イメージング技術の開発及び現場における実証例を紹介する。

論文

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

佐藤 優樹; 峯本 浩二郎*; 根本 誠*; 鳥居 建男

Nuclear Instruments and Methods in Physics Research A, 976, p.164286_1 - 164286_6, 2020/10

 被引用回数:6 パーセンタイル:91.19(Instruments & Instrumentation)

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., experienced a meltdown as a result of a large tsunami caused by the Great East Japan Earthquake on March 11, 2011. At that time, it was necessary to understand the aspects of the decommissioning working environment inside the FDNPS, such as establishing how the radioactive substances were distributed across the site, for work to be done efficiently without exposure to large amounts of radiation. Therefore, virtual reality (VR) emerged as a solution. There have been previous reports done on a technique for visualizing the distribution of radioactive substances in three dimensions utilizing a freely moving gamma-ray imager combined with simultaneous localization and mapping (SLAM) technology. In this paper, we introduce imaging technologies for the acquisition of image data from radioactive substances and three-dimensional (3D) structural models of the working environment, using a freely moving gamma-ray imager combined with SLAM technology. For this research, we also constructed a VR system and displayed the 3D data in a VR space, which enables users to experience the actual working environment without radiation exposure. In creating the VR system, any user can implement this method by donning an inexpensive head-mounted display apparatus and using a free, or low-cost, application software.

論文

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

佐藤 優樹; 鳥居 建男

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

 被引用回数:2 パーセンタイル:66.08(Nuclear Science & Technology)

The Fukushima Daiichi Nuclear Power Station (FDNPS) suffered a meltdown as a result of a large tsunami triggered by the Great East Japan Earthquake on March 11, 2011. Understanding the distribution of radioactive substances inside the FDNPS is essential to execute appropriate decommissioning tasks. In this paper, we propose method for visualizing three-dimensional (3D) images of radioactive substances as a point cloud data (PCD) and integrating these data into 3D environment models. To demonstrate the usefulness of the proposed methods, a Compton camera was first employed to capture 3D images of radiation sources. The resulting PCD were then integrated into a 3D environment model of a measurement area acquired using the 3D light detection and ranging (LiDAR). This allowed in successful construction of a map to visually recognize the positions of radiation sources.

論文

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

佐藤 優樹; 鳥居 建男

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

 被引用回数:0 パーセンタイル:20(Nuclear Science & Technology)

The authors have requested the retraction of their article due to an identified defect in the Compton camera software, which resulted in an incorrect output value for the interaction position of the gamma rays in the sensor of the camera. It is expected that the experimental results may not change significantly with the bug correction; however, many figures would need to be replaced. The authors may seek a separate publication of an updated manuscript in the future.

論文

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

佐藤 優樹; 小澤 慎吾*; 寺阪 祐太; 峯本 浩二郎*; 田村 智志*; 新宮 一駿*; 根本 誠*; 鳥居 建男

Journal of Nuclear Science and Technology, 57(6), p.734 - 744, 2020/06

 被引用回数:7 パーセンタイル:94.21(Nuclear Science & Technology)

The Fukushima Daiichi Nuclear Power Station, operated by Tokyo Electric Power Company Holdings, Inc., suffered a meltdown as a result of a large tsunami triggered by the Great East Japan Earthquake on March 11, 2011. To proceed with the environmental recovery by decontamination, drawing a radiation distribution map that can indicate the distribution of radioactive substances is extremely important to establish detailed decontamination plans. We developed a remote radiation imaging system consisting of a lightweight Compton camera and a multi-copter drone to remotely measure the distribution of the radioactive substances. This system can perform radiation imaging using a Compton camera while flying and moving. In addition, it is also possible to draw the distribution of radioactive substances three-dimensionally by projecting the radiation image measured with the Compton camera on a three-dimensional topography model separately acquired by a 3D-LiDAR. We conducted a survey of radioactive hotspots in difficult-to-return zone in the coastal area of Fukushima, Japan. The drone system succeeded in three-dimensional visualization of several hotspots deposited on the ground. Such remote technology would be useful not only for monitoring the difficult-to-return zone, but also for monitoring distribution of radioactive substances inside the site of the FDNPS where decommissioning work is ongoing.

論文

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

寺阪 祐太; 渡辺 賢一*; 瓜谷 章*; 山崎 淳*; 佐藤 優樹; 鳥居 建男; 若井田 育夫

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

For the application in the measurement of the high dose rate hot spots inside the Fukushima Daiichi Nuclear Power Station buildings, we propose a wavelength-resolved type one-dimensional radiation distribution sensing method using plastic scintillating fiber (PSF). The proposing method estimates the incident position of radiation to the PSF by the unfolding of the wavelength spectrum output from the fiber edge using the fact that the attenuation length of scintillating light depends on the wavelength. By measuring the response function in advance, which defined as the wavelength spectrum measured at the fiber edge by the spectrometer with every transmission distance, the spectrum which can obtain when measured a certain radiation distribution can be expressed as the convolution of the response function. This method can avoid the problem of chance coincidence effect and signal pile-up, which occurs in the radiation detector with pulse counting mode under high dose rate field because this method measures the integrated light intensity. Through basic experiment using the ultraviolet irradiation source and $$^{90}$$Sr point source, basic properties of inverse estimation of irradiated position were confirmed, which showed that source position was reasonably estimated using the response function which obtained by the ultraviolet irradiation source in advance.

論文

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

北山 佳治; 寺阪 祐太; 佐藤 優樹; 鳥居 建男

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

At the Fukushima Daiichi Nuclear Power Station (FDNPS), various works are under-way for decommissioning. Depending on work places, there are radioactive hotspot. Therefore measuring the position of the hotspot in advance is important for safety of the worker. The system that can easily measure the dose rate distribution in work place has been demanded. There are two methods for imaging a dose rate distribution: a pinhole camera and a Compton camera. A pinhole camera can determine direction of radiation source in one event, but the weight becomes heavy because a shield is required. On the other hand, since the Compton camera does not require a shield, it can be reduced in the size and weight. However, Compton imaging method generate many ghosts of cone traces, which reduce the signal-to-noise ratio. We propose a new gamma-ray imager that works like a pinhole camera without a shield. This is achieved by arranging directional gamma ray detectors that does not require a shield. In this work, we have performed principle verification of a directional gamma-ray detector that is a basic component of the new gamma-ray imager by using Geant4 Monte Carlo simulation.

論文

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

佐藤 優樹; 鳥居 建男

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

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., suffered a meltdown as a result of a large tsunami triggered by the Great East Japan Earthquake on March 11, 2011. We have been conducting demonstration tests for detection of radioactive hotspots inside the FDNPS buildings using a Compton camera, a kind of gamma-ray imager. In this work, we introduced the 3D visualization of radioactive substances by using combination of the Compton camera and optical camera based on Structure from Motion (SfM). By taking photographs of the experimental environment while freely moving, a 3D structural model of the environment can be reconstructed from the multiple photographs, and the movement trajectory of the optical camera can be estimated simultaneously using the SfM. Furthermore, the radioactive substances can be visualized by drawing an image of the radioactive substances on the 3D structural model using gamma-ray data acquired by the Compton camera. In the demonstration, we succeeded in visualizing a $$^{137}$$Cs-radiation source on the 3D structural model of the experimental environment while freely moving these devices. This technology is useful for making it easy to recognize radioactive substances in decommissioning work site such as the FDNPS.

論文

最先端の研究開発,日本原子力研究開発機構,2; 1Fの廃炉と環境回復をめざして,2

佐藤 優樹; 川瀬 啓一; 飯島 和毅; 小林 卓也

日本原子力学会誌ATOMO$$Sigma$$, 62(1), p.37 - 41, 2020/01

原子力機構の研究開発の最前線を紹介する。2回目となる今回は、福島第一原子力発電所(1F)の廃炉と環境回復を目指して(2)について紹介する。

論文

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

佐藤 優樹; 寺阪 祐太; 宇津木 弥*; 菊地 弘幸*; 清岡 英男*; 鳥居 建男

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

 被引用回数:16 パーセンタイル:96.51(Nuclear Science & Technology)

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., went into meltdown in the aftermath of a large tsunami caused by the Great East Japan Earthquake of 11 March 2011. Measurement of radiation distribution inside the FDNPS buildings is indispensable to execute decommissioning tasks in the reactor buildings. We conducted a radiation imaging experiment inside the reactor building of Unit 1 of FDNPS by using a compact Compton camera mounted on a crawler robot and remotely visualized gamma-rays streaming from deep inside the reactor building. Moreover, we drew a radiation image obtained using the Compton camera onto the three-dimensional (3-D) structural model of the experimental environment created using photogrammetry. In addition, the 3-D model of the real working environment, including the radiation image, was imported into the virtual space of the virtual reality system. These visualization techniques help workers recognize radioactive contamination easily and decrease their own exposure to radiation because the contamination cannot be observed with the naked eye.

論文

Image reconstruction of radioactive contamination due to the Fukushima-Daiichi Nuclear Power Station Accident using a compact Compton camera

佐藤 優樹; 寺阪 祐太; 宮村 浩子; 冠城 雅晃; 谷藤 祐太; 川端 邦明; 鳥居 建男

Reactor Dosimetry; 16th International Symposium on Reactor Dosimetry (ISRD-16) (ASTM STP 1608), p.428 - 436, 2018/11

 被引用回数:0 パーセンタイル:0.05

We developed a lightweight compact Compton camera to measure the distribution of radioactive contamination inside the Fukushima Daiichi Nuclear Power Station. We conducted performance evaluation tests in the coastal area of Fukushima, Japan, using the camera, which employs a cerium (Ce)-doped GAGG (Gd$$_{3}$$Al$$_{2}$$Ga$$_{3}$$O$$_{12}$$) scintillator coupled with a multipixel photon counter. The camera can clearly visualize spreading of radioactivity along the ground surface. In addition, we performed three-dimensional image reconstruction of the distribution of radioactive contamination using the multi-angle data obtained with the Compton camera. We succeeded in obtaining a three-dimensional image of radioactive contamination in the outdoor area.

論文

Gamma-ray imaging system for Fukushima Daiichi Nuclear Power Plant using silicon strip detector

冠城 雅晃; 佐藤 優樹; 吉原 有里*; 島添 健次*; 高橋 浩之*; 鳥居 建男

Reactor Dosimetry; 16th International Symposium on Reactor Dosimetry (ISRD-16) (ASTM STP 1608), p.405 - 414, 2018/11

 被引用回数:0 パーセンタイル:0.05

On March 11, 2011, a massive earthquake occurred in the Tohoku region of Japan, and a large tsunami hit the Fukushima Daiichi Nuclear Power Plant (1F), resulting in a nuclear accident. Despite the years that have passed since the accident, decommissioning remains a concern. Radiation measurement techniques are very important for accelerating the decommissioning and ensuring low radiation exposure to workers. Our gamma-ray imaging system is the detection device for determining the three dimensional radioactive distributions of nuclear fuel debris, measuring high-energy gamma rays (greater than 1 MeV). Silicon semiconductor detectors are among the candidate detectors for radiation measurements in our system because of their radiation-hardness and high counting rate capability. We have been developing a stacked amorphous-silicon (Si)/crystal-Si heterojunction Si strip detector, which has 1-mm-pitch striped electrodes (0.5 mm wide) and 1.2-mm-pitch stacked technology. The detector consists of an Si strip mounted on a thin printed circuit board, front-end readout electronics with a complementary metal oxide semiconductor application specific integrated circuit, and a field programmable gate array. The threshold level of energy deposition of each pulse signal in each channel can be set from the application-specific integrated circuit, and gamma-ray images with energy discrimination can be obtained. The energy threshold level for discrimination of $$^{60}$$Co gamma rays from $$^{137}$$Cs gamma rays was investigated experimentally and by means of simulation, and it was found to be about 500 keV. Therefore, our Si strip detector has the required position sensitivity and energy discrimination ability for identifying high-energy gamma-ray source distributions.

論文

Radiation imaging using a compact Compton camera inside the Fukushima Daiichi Nuclear Power Station building

佐藤 優樹; 谷藤 祐太; 寺阪 祐太; 宇佐美 博士; 冠城 雅晃; 川端 邦明; 宇津木 弥*; 菊地 弘幸*; 高平 史郎*; 鳥居 建男

Journal of Nuclear Science and Technology, 55(9), p.965 - 970, 2018/09

 被引用回数:15 パーセンタイル:90(Nuclear Science & Technology)

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., went into meltdown after the occurrence of a large tsunami caused by the Great East Japan Earthquake of March 11, 2011. The radiation distribution measurements inside the FDNPS buildings are indispensable to execute decommissioning tasks in the reactor buildings. We conducted the radiation imaging experiment inside the turbine building of Unit 3 of the FDNPS using a compact Compton camera, and succeeded in visualizing the high-dose contamination (up to 3.5 mSv/h). We also drew a three-dimensional radiation distribution map inside the turbine building by integrating the radiation image resulting from the Compton camera into the point cloud data of the experimental environment acquired using the scanning laser range finder. The radiation distribution map shows the position of these contaminations on the real space image of the turbine building. The radiation distribution map helps workers to easily recognize the radioactive contamination and to decrease the radiation exposure; the contamination cannot be observed with the naked eye, naturally.

論文

A 3D radiation image display on a simple virtual reality system created using a game development platform

佐藤 優樹; 寺阪 祐太; 小澤 慎吾*; 谷藤 祐太; 鳥居 建男

Journal of Instrumentation (Internet), 13(8), p.T08011_1 - T08011_10, 2018/08

 被引用回数:4 パーセンタイル:27.23(Instruments & Instrumentation)

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., suffered a meltdown after a large tsunami caused by the Great East Japan Earthquake on March 11, 2011. The measurement of radiation distribution inside FDNPS buildings is indispensable for executing appropriate decommissioning tasks in the reactor's buildings. In addition, it is extremely important to accurately predict the location of radioactive contamination beforehand because the working time is limited owing to radiation exposure to workers. In this paper, a simple virtual reality (VR) system that can detect radioactive substances in virtual space has been developed to simulate real working environments. A three-dimensional (3D) photo-based model of the real working environment, including an image of the radioactive substance, was imported into the virtual space of the VR system. The developed VR system can be accessed using a smartphone and a cardboard goggle. The VR system is expected to be useful for preliminary training of workers and for recognizing radioactive hotspots during decommissioning of the work environment.

論文

放射線分布の3次元イメージング技術

佐藤 優樹; 鳥居 建男

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

東京電力ホールディングス福島第一原子力発電所(以下、福島第一原発という)の円滑な廃炉作業に向けて、日本原子力研究開発機構廃炉国際共同研究センターでは、放射線イメージングセンサーとして大きな遮蔽体の要らない小型コンプトンカメラを用い、放射性物質の立体的な分布を示そうと、福島第一原発の作業環境において放射線物質の3次元可視化技術の研究開発に取り組んでいる。本研究開発では、レーザー光を利用した測域センサー(LiDAR)で取得した建屋構造物の3次元モデルにコンプトンカメラで取得される汚染分布の情報を重ね合わせることにより、実空間における汚染分布の拡がりをより詳細に可視化する手法を検討している。本稿では、これらの技術と取り組みについて紹介する。

論文

A Three-dimensional radiation image display on a real space image created via photogrammetry

佐藤 優樹; 小澤 慎吾*; 谷藤 祐太; 鳥居 建男

Journal of Instrumentation (Internet), 13(3), p.P03001_1 - P03001_8, 2018/03

 被引用回数:5 パーセンタイル:35.25(Instruments & Instrumentation)

The Fukushima Daiichi Nuclear Power Station (FDNPS), operated by Tokyo Electric Power Company Holdings, Inc., went into meltdown after the large tsunami caused by the Great East Japan Earthquake of March 11, 2011. Radiation distribution measurements inside FDNPS buildings are indispensable to execute decommissioning tasks in the reactor buildings. We have developed a method of three-dimensional (3-D) image reconstruction for radioactive substances using a compact Compton camera. We also succeeded in visually recognize the position of the radioactive substances on the real space by integration of the 3D radiation image and the 3D photo-model created by photogrammetry.

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