Pulse shape analysis for Ge semiconductor Compton camera

The Compton camera has found applications in many fields such as medical imaging, astrophysics, environmental monitoring and nuclear non-proliferation. We are developing a $\gamma $-ray Compton camera for medical use of multiple molecular imaging, which we call GREI (Gamma-Ray Emission Imaging). The GREI system consists of two double-sided orthogonal-strip high-purity germanium semiconductor detectors. Each detector can detect the interaction position and deposited energy of $\gamma $ ray, and $\gamma $-ray source distributions can be visualized based on Compton scattering kinematics. In order to improve the imaging resolution of the GREI, a pulse shape analysis techniques is under development. In general for the segmented semiconductor detector, its output pulses have variety of the shapes depending on the $\gamma $-ray interaction positions. Therefore, by analyzing the pulse shape, interaction position of $\gamma $-ray interaction can be extracted. Especially, analyzing not only pulse shape appearing in $\gamma $-ray hit segment but also transient signals in neighboring segments, 3D interaction position within the electrode can be extracted. We implemented a pulse shape analysis system for GREI and succeeded to extract 3D interaction position in sub-millimeter order. Consequently, imaging resolution is vastly improved.