We have been developed an electron tracking Compton camera (ETCC) using an SOI pixel semiconductor detector for observation sub MeV gamma rays. An electron tracking Compton camera can reconstruct arrival directions of gamma rays event by event as a point using the recoil directions of electron tracks , so this camera does not increase false spot comparing with a classical Compton camera. Also, an ETCC can discriminate between the gamma rays and backgrounds by detecting the track length and energy of recoil electrons. In addition, ETCC using a semiconductor detector is useful for detecting line gamma rays because of its high energy resolution. We focused on a n SOI pixel semiconductor detector, which has a small pixel pitch of a few ten um. The sensor has a trigger circuit mounted on each pixel, so we can select only candidate
gamma ray events and readout only the selected pixels. We developed a prototype Compton camera using XRPIX2b sensor, which is an SOI pixel sensor developed by Kyoto University. We evaluated the detection capability of recoil electron due to 511 keV gamma rays while changing various conditions such as scattering angle and incident directions of gamma rays. From the results of the evaluation in the laboratory, we succeeded in detecting recoil electron tracks and estimating the recoil directions using the track image. Furthermore, we confirmed to be able to detect the radioisotope position using back projection method.
We obtained sufficient quantitative detailed performance data of the current sensor to develop a novel sensor for ETCC.