First demonstration of electron-tracking based Compton imaging in solid-state detectors

We report on the first demonstration of electron-tracking based Compton-scatter gamma-ray imaging in a solid-state detector. Employing a high-resolution and fully depleted charge coupled device (CCD) we were able to measure the initial direction of the Compton-scattered electron enabling the reconstruction of the incident direction of a gamma-ray on an event-by-event basis. The scatter direction was deduced by analyzing the electron energy loss measured on the pixilated readout plane. Employing a 650 μm thick Si-based CCD with 10.5 μm pixel size, the measured energy loss was not only used to deduce the electron-scatter angle in the pixel plane but also in the angle perpendicular and out of the pixel plane. The latter was accomplished by relating the measured energy loss to a calculated energy loss, which is predicted using the measured energy per pixel. Combining the Compton-scatter information obtained in the CCD detector with the energy and three-dimensional position information of the scattered gamma-ray measured in a Ge detector in double-sided strip configuration, we were able to reconstruct the incident direction of the gamma-ray. This measurement demonstrates the feasibility of using Si-based devices to enable electron-tracking based Compton imaging and promises significantly increased sensitivity over conventional Compton imaging instruments or gas-based imagers, which lack in overall detection sensitivity due to the low density.