Compton camera coincidences in the silicon drift detector

A Compton camera system consisting of a silicon drift detector (SDD) and an Anger camera has been constructed to study coincidence events and the possibility of tracking a recoil electron. An event is considered as a coincidence when a photon emitted from a radioactive source is first Compton scattered in the SDD where the recoil electron deposits its energy and the scattered photon undergoes a photoelectric absorption in the NaI(Tl) crystal of the Anger camera. SDD is composed of a monolithic array of 19 cells each having an on-chip transistor which provides the first stage amplification. ¹³⁷Cs source has been finely collimated in order to study events occurring at different locations within a single cell. Electron tracks depositing energy in multiple cells have also been studied by considering time coincidences between SDD cells and the Anger camera. The equipment is designed such that the measurements can be done in all detector orientations and kinematical conditions. The angular and energy distribution of coincidence events have been studied with high statistics. Energy resolution and angle measurements performed with this detector system will be presented in this paper.