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佐藤 優樹; 角藤 壮*; 田中 孝幸*; 嶋野 寛之*; 諸橋 裕子; 畠山 知圭*; 中島 準作; 石山 正弘
Nuclear Instruments and Methods in Physics Research A, 1063, p.169300_1 - 169300_7, 2024/06
A system for locating radioactive substances using a hexapod robot equipped with a Compton camera and light detection and ranging camera was developed, and its performance evaluation test was conducted at FUGEN, a nuclear facility owned by Japan Atomic Energy Agency. In the test, by projecting images of radioactive substances acquired with the Compton camera onto a three-dimensional model of the work environment acquired with a light detection and ranging camera, the locations where radioactive substances have accumulated and the dose rate is higher than the surrounding area were successfully visualized and identified.
寺阪 祐太; 佐藤 優樹; 瓜谷 章*
Nuclear Instruments and Methods in Physics Research A, 1062, p.169227_1 - 169227_6, 2024/05
We have developed a new position-sensitive optical fiber radiation sensor that achieves single-end readout and high dose rate application. The sensor determines the incident position of radiation on the optical fiber by using the wavelength dependency of light attenuation within the fiber. Through the analysis of the output wavelength spectrum from the fiber end, the incident position of radiation on the optical fiber can be inversely estimated using the spectrum unfolding procedure. Using this optical fiber sensor, we conducted a measurement of radiation distribution inside the Fukushima Daiichi Nuclear Power Station (FDNPS). The actual trend of incident position of radiation was successfully reproduced in a high dose rate area, with a maximum dose rate exceeding 100 mSv/h. This validates the effectiveness of our new position-sensitive optical fiber radiation sensor.
森下 祐樹; 宮村 浩子; 佐藤 優樹; 大浦 正利*
Radiation Measurements, 171, p.107064_1 - 107064_7, 2024/02
被引用回数：0 パーセンタイル：0.08(Nuclear Science & Technology)アルファおよびベータ汚染位置の検出は、核施設の除染にとって重要である。廃炉現場の高線量率環境では、作業員による直接の汚染測定は困難である。そこで、新しいシンチレータベースの検出器を用いた遠隔自動汚染測定システムを開発した。50mm
厚さ100
mのYAlO
(Ce)(YAP:Ce)シンチレータにフラットパネル型マルチアノード光電子増倍管を結合させた。検出器はロボットの下部に下向きに設置された。エネルギー測定機能があり、エネルギー測定によりアルファ粒子とベータ粒子および
Rnアルファ粒子を識別できる。エネルギー情報を使用すると、アルファ粒子とベータ粒子を同時に識別し、マッピングすることができる。さらに、ゆっくりと動くロボットを使用すると、1回の測定で統計的に十分なカウントを取得できるため、アルファ粒子のみを使用して表面汚染密度を評価できる。遠隔自動汚染測定システムは、作業員が立ち入ることができない環境における汚染分布の可視化に役立つ。
佐藤 優樹
Applied Radiation and Isotopes, 203, p.111083_1 - 111083_9, 2024/01
被引用回数：0 パーセンタイル：0.01(Chemistry, Inorganic & Nuclear)At the Fukushima Daiichi Nuclear Power Station (FDNPS), radioactive substances released during the accident were deposited on various equipment and building structures. During the decommissioning work, an investigation of the deposition of radioactive substances inside the contaminated equipment and structures can provide information on the cause and progression of the accident. This study introduces a quantitative evaluation method of radioactivity using a Compton camera, a type of gamma-ray imager, to investigate the deposition and contamination level of radioactive substances on contaminated objects at the FDNPS. Multiple 
Cs radiation sources with varying radioactivity were placed horizontally in one dimension within the field of view of the Compton camera, and a proof-of-principle study was conducted to evaluate the radioactivity of each source quantitatively.
佐藤 優樹
知能と情報, 35(4), p.81 - 86, 2023/11
福島第一原子力発電所(1F)事故により1Fサイト内外に飛散・沈着した放射性物質の分布を3次元的に可視化するために、放射性物質可視化カメラであるコンプトンカメラに、3次元測域センサを基盤とした環境認識デバイスやドローンを組み合わせた統合型放射線イメージングシステムiRIS(アイリス: integrated Radiation Imaging System)の開発を進めている。本稿では、iRISのコンセプトおよびその原理を説明するとともに、1Fサイト内ならびに帰還困難区域におけるホットスポット可視化の実証例を紹介する。
佐藤 優樹; 寺阪 祐太
Journal of Nuclear Science and Technology, 60(8), p.1013 - 1026, 2023/08
被引用回数：5 パーセンタイル：98.48(Nuclear Science & Technology)The Fukushima Daiichi Nuclear Power Station (FDNPS) suffered a meltdown in the aftermath of the large tsunami caused by the Great East Japan Earthquake that occurred on 11 March 2011. A massive amount of radioactive substance was spread over a wide area both inside and outside the FDNPS site. In this study, we present an approach for visualizing a radioactive hotspot on a standby gas-treatment system filter train, a highly contaminated piece of equipment in the air-conditioning room of the Unit 2 reactor building of FDNPS, using radiation imaging based on a Compton camera. In addition to fixed-point measurements using only the Compton camera, data acquisition while moving using an integrated Radiation Imaging System (iRIS), which combines a Compton camera with a simultaneous localization and mapping device and a survey meter, enabled the three-dimensional visualization of the hotspot location on the filter train. In addition, we visualized the hotspot and quantitatively evaluated its radioactivity. Notably, the visualized hotspot location and estimated radioactivity value are consistent with the accident investigation report of the FDNPS. Finally, the extent to which the radioactivity increased the ambient dose equivalent rate in the surrounding environment was explored.
佐藤 優樹; 峯本 浩二郎*; 根本 誠*
Radiation Protection Dosimetry, 199(8-9), p.1021 - 1028, 2023/06
被引用回数：1 パーセンタイル：68.31(Environmental Sciences)Identifying and visualizing the radiation source location are important in reducing the exposure dose of workers at the decommissioning site of the Fukushima Daiichi Nuclear Power Station and in improving the radiation protection functions in other sites where radiation sources are handled. In this paper, we developed the COMpton camera for Radiation Imaging System (COMRIS) to identify and visualize the radiation source location in 3D using output data from a Compton camera and a simultaneous localization and mapping (SLAM) device as input data. Here, we presented COMRIS to visualize a Cs-radiation source in a dark environment using data acquired by a commercial Compton camera and a LiDAR-based SLAM device mounted on a robot as input data. The radiation source image obtained using the Compton camera was drawn on the 3D work environment model acquired by the SLAM device, and the radiation source location was visible in 3D.
佐藤 優樹
Applied Radiation and Isotopes, 195, p.110739_1 - 110739_9, 2023/05
被引用回数：2 パーセンタイル：87.3(Chemistry, Inorganic & Nuclear)In the decommissioning work environment of a nuclear power plant, it is essential to accurately identify the location of radiation sources to reduce worker doses and develop decontamination plans. In this regard, gamma-ray imagers are promising devices in the visualization of the location of radiation sources. However, they can only estimate the direction in which the radiation source is located and not the distance to the source. A previous study has reported a method to identify the three-dimensional coordinates of the radiation source by measuring from multiple viewpoints with a gamma-ray imager. In some cases, the many pieces of object located at the actual decommissioning site limit the accessible area, making it difficult to measure the target area from multiple viewpoints. Thus, the present study devised and demonstrated a method of estimating the distance to the radiation source by measuring from only one direction using a Compton camera, a type of gamma-ray imager. The proposed method considered the reconstructed image intensity to be proportional to the inverse square of the distance to radiation source. This approach will be useful in accurately locating radiation sources in environments with limited workable areas, such as the broken reactor buildings inside the Fukushima Daiichi Nuclear Power Station.
佐藤 優樹
Applied Radiation and Isotopes, 185, p.110254_1 - 110254_7, 2022/07
In a radiation environment, such as the decommissioning site of a nuclear power station, visualization of the distribution of radioactive substances and estimation of the dose equivalent rate around the site can help reduce the exposure dose of workers and plan their work. The author has developed a method of visualizing the existence of a radiation source using a gamma-ray imager, estimating its radioactivity, and estimating the dose equivalent rate around the source. A Compton camera, which is a gamma-ray imager, is used to visualize the existence of a Cs radiation source and estimate its radioactivity, and a three-dimensional (3D) model of the region around the source is generated using a simultaneous localization and mapping device based on 3D light detection and ranging. Next, the dose equivalent rate around the source is calculated by importing the 3D model data and radioactivity information into a particle and heavy ion transport code system code. The validity of the calculated dose equivalent rates was confirmed by comparing them with values measured using a survey meter. This method can be used not only to simply visualize a source and calculate the dose equivalent rate around it but also to evaluate how addition of shielding or removal of contaminated objects can contribute to reducing the dose equivalent rate.
佐藤 優樹
Isotope News, (781), p.19 - 23, 2022/06
福島第一原子力発電所(1F)事故により1Fサイト内外に飛散・沈着した放射性物質の分布を3次元的に可視化するために、放射性物質可視化カメラであるコンプトンカメラに、3次元測域センサを基盤とした環境認識デバイスやドローンを組み合わせることによる放射線イメージングシステムを開発した。本稿では、放射性物質の分布を3次元的に可視化する手法についてその原理を説明するとともに、1Fサイト内ならびに帰還困難区域におけるホットスポット可視化の実証例を紹介する。
佐藤 優樹; 寺阪 祐太
Journal of Nuclear Science and Technology, 59(6), p.677 - 687, 2022/06
被引用回数：17 パーセンタイル：95.29(Nuclear Science & Technology)The Fukushima Daiichi Nuclear Power Station (FDNPS) went into meltdown after being hit by a large tsunami caused by the Great East Japan Earthquake on March 11, 2011. Measuring and understanding the distribution of radioactive contamination inside the FDNPS is essential for decommissioning work, reducing exposure to workers, and ensuring decontamination. This paper reports the visualization tests of radioactive contamination in the Unit 1/2 exhaust stack of the FDNPS using a compact Compton camera. Fixed-point measurements were conducted using only a Compton camera and moving measurements using an integrated radiation imaging system (iRIS) that combines a Compton camera with a simultaneous localization and mapping device. For the moving measurements, an operator carrying the iRIS acquires data continuously while walking in a passage near the stack. With both types of measurements, high-intensity contamination was detected at the base of the stack, and detailed three-dimensional (3D) visualization of the contamination was obtained from the moving measurement. The fixed-point measurements estimated the source intensity of the contamination from the reconstructed contamination image acquired by the Compton camera. Furthermore, workers can experience the work environment before actual work by importing a 3D structure model into a virtual reality system displaying the contamination image.
佐藤 優樹
検査技術, 27(5), p.9 - 15, 2022/05
福島第一原子力発電所サイト内に飛散・沈着した放射性物質の分布を3次元的に可視化する統合型放射線イメージングシステム(iRIS)について、その原理と実証例を紹介する。
鳥居 建男*; 眞田 幸尚; 佐藤 優樹
日本原子力学会誌ATOMO
, 64(1), p.17 - 22, 2022/01
福島第一原子力発電所の事故から10年が経過した。事故により福島第一原子力発電所建物やサイト内だけでなく環境中にも広く放射性物質が拡散沈着したことから、事故発生直後より放射線源の空間分布を直感的に把握できる放射線源の可視化への要求が高まり、環境中における放射線分布のマッピングやガンマカメラと呼ばれる放射線のイメージング装置の投入と開発が進められてきた。ここでは、事故後に開発され運用されてきた放射線分布の計測技術について紹介するとともに、今後の展望について述べる。
持丸 貴則*; 小泉 光生; 高橋 時音; 弘中 浩太; 木村 祥紀; 佐藤 優樹; 寺阪 祐太; 山西 弘城*; 若林 源一郎*
第42回日本核物質管理学会年次大会会議論文集(インターネット), 4 Pages, 2021/11
日本原子力研究開発機構では、文部科学省核セキュリティ強化等補助事業の下、大規模公共イベント等において、核・放射性物質を用いたテロ行為等を未然に防ぐため、イベント会場にそれらが持ち込まれた場合に迅速に検知するための技術・装置の開発を目的とし、広域における放射性物質検知技術開発を4年計画で進めている。本講演では、プロジェクトの概要を説明するとともに、技術開発の進捗状況を一部紹介する。
佐藤 優樹; 峯本 浩二郎*; 根本 誠*
Journal of Instrumentation (Internet), 16(10), p.C10008_1 - C10008_8, 2021/10
被引用回数：3 パーセンタイル：28.05(Instruments & Instrumentation)At the Fukushima Daiichi Nuclear Power Station (FDNPS) where the accident occurred due to large tsunami caused by the Great East Japan Earthquake of 11 March 2011, it is important to understand and visualize the distribution of radioactive substances in order to reduce exposure doses of workers and to establish decontamination plans. We focused on the importance of visualizing beta-emitting nuclides in addition to gamma-emitting ones to reduce the exposure dose of workers at the FDNPS, and proposed a method for three-dimensional (3-D) visualizing the position of beta-emitting ones. By combining directional Geiger-Mueller counter with Structure from Motion technology using a digital camera, we succeeded in visualizing a beta-emitting nuclide of 
Sr-source on the 3-D model of the working environment.
佐藤 優樹; 峯本 浩二郎*; 根本 誠*; 鳥居 建男
Journal of Nuclear Engineering and Radiation Science, 7(4), p.042003_1 - 042003_12, 2021/10
Technology for measuring and identifying the positions and distributions of radioactive substances is important for decommissioning work sites at nuclear power stations. A three-dimensional (3D) image reconstruction method that locates radioactive substances by integrating Structure-from-Motion (SfM) with a Compton camera (a type of gamma-ray imager) has been developed. From the photographs captured while freely moving in an experimental environment, a 3D structural model of the experimental environment was created. By projecting the radioactive substance image acquired by the Compton camera on the 3D structural model, the positions of the radioactive substance were visualized in 3D space. In a demonstration study, the Cs-radiation source was successfully visualized in the experimental environment captured by the freely moving cameras. In addition, how the imaging accuracy is affected by uncertainty in the self-localization of the Compton camera processed by SfM, and by positional uncertainty in the gamma-ray incidence determined by the sensors of the Compton camera was investigated. The created map depicts the positions of radioactive substances inside radiation work environments, such as decommissioning work sites at nuclear power stations.
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
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.
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Sr/Y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。
佐藤 優樹
Physics Open (Internet), 7, p.100070_1 - 100070_8, 2021/05
To understand radiation information, such as dose rate and the position of radioactive substances in a radioactive working environment in detail, the author proposes the construction of a mirror world of the environment. In the proposed mirror world, the work environment is reproduced in a virtual space, and the radiation information measured in a real space is projected onto the virtual space. Note that in addition to displaying the radiation information in the virtual space, the visualization result of the radiation information in the virtual space is used for decision-making in the real space. It is seen that the radiation measurement in the real space and visualization of measurement results in the virtual space always interact. In this report, the author introduces an example of building the mirror world based on radiation measurements performed in a laboratory using Cs as a radiation source. In the laboratory, the dose rate was measured by using a survey meter together with a device for the simultaneous localization and mapping based on three-dimensional (3D) light detection and ranging. The measured dose rate was mapped onto the work environment in the virtual space. Technologies developed by the author, for example, the 3D visualization of the radiation source based on an integration of the Compton camera and structure-from-motion technology and the virtual-reality experience technology of the work environment that displays the source image were also used. The technology to project the radiation-source image into the real space using augmented-reality is also introduced in this report.
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：2 パーセンタイル：30.55(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. 
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.
