Detection of Recoil Electron Tracks using an SOI Pixel Sensor for an Advanced Compton Camera

Sub-MeV line gamma-ray observations are important probes to elucidate various high-energy phenomena in astrophysics. An advanced Compton imaging technique is useful for detecting gamma rays in these bands. This camera can estimate an arrival direction of a gamma-ray event by event, thus, this camera can eliminate accidental events and false spots, which appear in a reconstructed image using a classical Compton camera. Furthermore, a semiconductor detector is essential for observing line gamma rays. In this study, we developed a prototype Compton camera using a silicon-on-insulator (SOI) pixel sensor. Using the prototype, we performed to detect recoil-electron tracks and estimated a recoil direction using a recoil-electron track. We succeeded in detecting electron tracks released from 511-keV gamma rays and estimating recoil directions. Furthermore, we reconstructed the arrival direction of a gamma ray and demonstrated to identify the source position by back-projection method. The angular resolution of an advanced Compton camera described two parameters, which is angular resolution measure (ARM) and scatter plane deviation (SPD). We obtained these tentative value from the reconstructed image. ARM and SPD are approximately 10° and 80-100°, respectively. For future plan, we will evaluate the quantitative detailed performances of the prototype under the various conditions.