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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.
C and 1500C and measurements of lifetime and photoluminescenceKlahold, W. M.*; Devaty, R. P.*; Choyke, W. J.*; Kawahara, Kotaro*; Kimoto, Tsunenobu*; Oshima, Takeshi
Materials Science Forum, 778-780, p.273 - 276, 2014/02
Son, N. T.*; Trinh, X. T.*; L
vile, L. S.*; Svensson, B. G.*; Kawahara, Kotaro*; Suda, Jun*; Kimoto, Tsunenobu*; Umeda, Takahide*; Isoya, Junichi*; Makino, Takahiro; et al.
Physical Review Letters, 109(18), p.187603_1 - 187603_5, 2012/11
Times Cited Count：199 Percentile：97.98(Physics, Multidisciplinary)Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
After the accident at the Fukushima Daiichi Nuclear Power Plant in March 2011, there are still areas in Fukushima Prefecture where residents cannot return due to radiation. In this study, we evaluated where radioactive materials would accumulate by visualizing the radiation distribution. Measurements were taken with a Compton camera (H400, H3D) in the area where residents cannot return. Gamma plotters (Gamma Plotter F, Japan Radiation Engineering) were used to measure the air dose rates at 0.05 and 1m above the ground in the entire area. It was found that the air dose rates were high around houses, near roads, and near puddles in depressions. The Compton camera measurements also confirmed the existence of hot spots along the side of the road. This is thought to be due to the accumulation of radionuclides that ran off from gravel and flat concrete where rainwater flows easily, in areas where rainwater tends to accumulate, such as rubble and ditches.
Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
In this study, the distribution of radioactive materials was measured in the Hamadori area of Fukushima prefecture using a Compton camera. Compton cameras are lightweight and capable of visualizing radiation distribution, which makes them useful for in-situ measurements. This time, in addition to the Compton camera, several instruments, such as a survey meter, were used to measure radiation and compare them. As a result, the radiation distribution (2D image) in the environment was clarified by the Compton camera. However, the distance to the hot spot cannot be grasped in the 2D image. Therefore, in order to grasp the radiation source in detail, we aim to create a 3D map of radiation source position and its intensity. Since the Compton camera requires the dose rate for each nuclides, we believe that it will lead to the prediction of the dose rate distribution in the future.
Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
In this study, measurements using a Compton camera and video images using an optical camera were taken in the difficult-to-return zone in Hamadori, Fukushima Prefecture. The locations of radionuclides were then confirmed by combining the video images with the radiation distribution images taken by the Compton camera. By photographing the hot spot from various positions and angles, the three-dimensional spatial extent of the radiation source could be confirmed. As a result of measurements at different distances from the hot spot, the dose rate in the direction of the hot spot photographed by the Compton camera was generally proportional to the inverse square of the distance when there was only one hot spot in front of the hot spot. However, this was not always the case when hot spots existed at multiple locations.
Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
As a result of the Fukushima Daiichi Nuclear Power Station accident, radioactive materials were dispersed into the environment from inside the nuclear reactor. Now that the difficult-to-return zone is being lifted, it is important to understand the radiation distribution in the surrounding area. At two locations in the difficult-to-return zone (Okuma Town), measurements were taken with a Compton camera and video was recorded with an optical camera. The locations of radionuclides were confirmed by combining the measurement data and video. The measurement equipment used included a Compton camera using a CZT (CdZnTe) semiconductor (H420 manufactured by H3D), a survey meter with a wand-type GPS (Gamma Plotter H manufactured by Japan Radiation Engineering Co., Ltd.) and an optical camera. Air dose rates at 1 m above ground level ranged from 4 to 46 
Sv/h at the first location and from 6 to 12 Sv/h at the second location. By photographing the high-dose points from various positions and angles, the three-dimensional spatial extent of the radiation source could be confirmed.
Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
Currently, the difficult-to-return zones are being lifted, and it is important to determine the radiation distribution. However, Compton cameras can only provide two-dimensional radiation information, and it is impossible to determine the distance to hot spots. Therefore, in order to obtain a more detailed distribution of radiation sources, we combined a Compton camera and an optical camera to create 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 vicinity of a private home. The distribution of air dose rates was determined by measurement with a survey meter with a wand-type GPS (Gamma Plotter H manufactured by Japan Radiation Engineering Co). Measurements were taken with a Compton camera (H420, H3D, USA) at several different positions and angles toward the hot spots. An optical camera (GoPro) was used to create three-dimensional images of the measurement site. The relationship between the air dose rate readable from the radiation source distribution map taken by the Compton camera and the distance from the hotspot was obtained.
Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
A Compton camera can only provide two-dimensional radiation information, and it is impossible to determine the distance to hot spots. In this study, in order to obtain more detailed radiation source distribution, we combined a Compton camera and an optical camera to create a three-dimensional distribution map of source locations and their intensities. The survey was conducted at two locations in the difficult-to-return zone: a park parking lot and the area around a private house in the difficult-to-return zone (Okuma Town). The distribution of air dose rates was ascertained by measurement with a survey meter with a stick-type GPS (Gamma Plotter H manufactured by Japan Radiation Engineering Co. Measurements were taken with a Compton camera (H420, H3D, USA) at different positions and angles toward the hot spots. The software (Application Programming Interface Example (APIE)) was used to check the radiation incident information (incident time, energy, x, y, z) obtained by the Compton camera in real time. In the future, we will use the incident radiation information obtained with APIE to estimate the position of the radiation.
Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
Currently, decontamination activities are being carried out in the Hamadori area, but it is difficult to make comprehensive measurements with portable survey meters. Therefore, there is a need for a technology to measure radiation distribution with a simple measuring device. In a previous study, radiation distribution was measured using a Compton camera capable of omni-directional measurement, which enabled a quick and simple evaluation of the location of hotspots at the measurement points. However, the distribution map obtained was a two-dimensional image and the distance to the hotspot could not be determined. The aim of this study was to create a three-dimensional image of the radiation distribution by combining radiation and optical images. The Compton camera will enable the identification of the sources of exposure of the population, as it will confirm not only the environmental radiation distribution but also the indoor radiation measurements.
Kawahara, Rika*; Ochi, Kotaro; Yamaguchi, Katsuhiko*; Torii, Tatsuo*
no journal, ,
Radiation distribution maps based on Compton cameras make it possible to identify hotspots where radioactive material has accumulated locally. However, the radiation distribution obtained is two-dimensional and the distance to the hotspot cannot be confirmed. In this study, a combination of a Compton camera and an optical camera was used to integrate the radiation distribution with optical images and to confirm the radiation source position and its spread, aiming at a detailed understanding of the radiation distribution. Field tests using a Compton camera (H3D, H420, USA) with a CZT (CdZnTe) semiconductor and an optical camera (GoPro) were carried out in the difficult-to-return zone, approximately 3.6 km away from the Fukushima Daiichi NPP. By taking images of the hotspot at different positions and angles, the location of the radiation source and its three-dimensional extent could be confirmed.
