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佐藤 優樹
Applied Radiation and Isotopes, 212, p.111421_1 - 111421_8, 2024/10
被引用回数：0 パーセンタイル：0.00(Chemistry, Inorganic & Nuclear)At the Fukushima Daiichi Nuclear Power Station, radiation sources released in the accident were deposited on various equipment and building structures. During decommissioning, it is crucial to understand the distribution of radiation sources and ambient dose equivalent rates to reduce worker exposure and implement detailed work planning. In this study, the author introduces a method for visualizing radiation sources, estimates their radioactivity using a Compton camera, and derives the dose rate around the radiation sources. In the demonstration test, the Compton camera was used to visualize radioactive hotspots caused by 
Cs radiation sources deposited in the outdoor environment and estimated the radioactivity. Furthermore, the dose rate around the hotspots was calculated from the estimated radioactivity, which confirmed that the calculated dose rate correlated with the dose rate measured using a survey meter. This approach is novel, where a series of analyses were conducted using the Compton camera to visualize radioactive hotspots, estimate the radioactivity, and derive the dose rate in the surrounding environment.
佐藤 優樹
Applied Radiation and Isotopes, 203, p.111083_1 - 111083_9, 2024/01
被引用回数：2 パーセンタイル：31.89(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; 寺阪 祐太
Journal of Nuclear Science and Technology, 60(8), p.1013 - 1026, 2023/08
被引用回数：12 パーセンタイル：98.13(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
Applied Radiation and Isotopes, 185, p.110254_1 - 110254_7, 2022/07
被引用回数：1 パーセンタイル：16.92(Chemistry, Inorganic & Nuclear)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; 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：22.61(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.
佐藤 優樹; 寺阪 祐太
no journal, ,
In this work, a method for estimating the radioactivity of multiple radiation sources using a Compton camera was proposed. Specifically, this method focuses on the fact that the image intensity obtained by measuring multiple radiation sources is reproduced by superposition of that of each radiation source. Images of radiation sources with known radioactivity are acquired in advance, and these images are multiplied by a factor and superimposed to reproduce the image acquired from multiple radiation sources. In a poster presentation, we will introduce the results of measuring two Cs radiation sources in the laboratory and estimating their radioactivity.
