Three-dimensional visualization of a beta-emitting nuclide by combining a directional Geiger-Mueller counter and structure from motion

At the Fukushima Daiichi Nuclear Power Station (FDNPS) where an accident occurred due to a large tsunami caused by the Great East Japan Earthquake, understanding the distribution of radioactive substances is important to reduce the exposure dose to workers and establish decontamination plans. We focused on the importance of visualizing beta-emitting radiation sources in addition to gamma-emitting ones and proposed a method for three-dimensionally (3D) visualizing the location of beta-emitting radiation sources, which is important in discussing the effective dose for the crystalline lens of the eye. In this report, we have developed a technique to visualize the location of beta-emitting radiation sources in 3D by combining a directional Geiger Mueller counter (G-M counter) with Structure from Motion (SfM). An image of Sr-90 beta-ray source reconstructed using a beta-ray detector was projected onto a 3D model of the measurement area created using SfM, and the source location is identified in 3D. Additionally, we estimated the radioactivity of the visualized source. Then, by combining the beta-ray detector with a Compton camera, distinguishing between beta-and gamma-emitting radiation sources was possible. This study was based on the concept of integrated radiation imaging system (iRIS), which integrates multiple radiation detectors and environmental recognition devices.