Yuri Yoshihara

Electron Pattern Recognition using trigger mode SOI pixel sensor for Advanced Compton Imaging

Compton imaging is a useful method for localizing sub MeV to a few MeV gamma-rays and widely used for environmental and medical applications. The direction of recoiled electrons in Compton scattering process provides the additional information to limit the Compton cones and increases the sensitivity in the system. The capability of recoiled electron tracking using trigger-mode Silicon-On-Insulator (SOI) sensor is investigated with various radiation sources. The trigger-mode SOI sensor consists of 144 by 144 active pixels with 30 μm cells and the thickness of sensor is 500 μm. The sensor generates the digital output when it is hit by gamma-rays and 25 by 25 pixel pattern of surrounding the triggered pixel is readout to extract the recoiled electron track. The electron track is successfully observed for 60Co and 137Cs sources, which provides useful information for future electron tracking Compton camera.

Erratum: Development of electron-tracking Compton imaging system with 30-μm SOI pixel sensor

Compton imaging is a useful method to localize gamma sources without using mechanical collimators. In conventional Compton imaging, the incident directions of gamma rays are estimated in a cone for each event by analyzing the sequence of interactions of each gamma ray followed by Compton kinematics. Since the information of the ejection directions of the recoil electrons is lost, many artifacts in the shape of cone traces are generated, which reduces signal-to-noise ratio (SNR) and angular resolution. We have developed an advanced Compton imaging system with the capability of tracking recoil electrons by using a combination of a trigger-mode silicon-on-insulator (SOI) pixel detector and a GAGG detector. This system covers the 660–1330 keV energy range for localization of contamination nuclides such as 137Cs and 134Cs inside the Fukushima Daiichi Nuclear Power Plant in Japan. The ejection directions of recoil electrons caused by Compton scattering are detected on the micro-pixelated SOI detector, which can theoretically be used to determine the incident directions of the gamma rays in a line for each event and can reduce the appearance of artifacts. We obtained 2-D reconstructed images from the first iteration of the proposed system for 137Cs, and the SNR and angular resolution were enhanced compared with those of conventional Compton imaging systems.