Position and depth of interaction measurements using silicon photostrip detectors and CsI(Tl) crystal

The photoelectric absorption of gamma rays in silicon occurs with such low probability that scintillation material is employed in the photostrip detector. We fabricate single-sided photostrip sensors which are sensitive to visible light. Two photodetectors in a photon counting mode are optically coupled with the scintillator with a sandwich structure. The photostrip sensors have 128 strips, a 200μm strip pitch and a size of 3.8×2.8cm². Sensor signals are read by a 128-channel VA1TA3 readout chip. A CsI(Tl) crystal is then optically combined to measure both of depths of interaction (DOI) and 2-D images, while the position of the LED are varied. We also performed a simulation of gamma ray irradiation at different locations inside the scintillator using the GEANT4 Monte Carlo simulation tool. We measured the 2-D position of incoming light with two photostrip sensors, and also measured the DOI and 2-D position of scintillating light by placing a scintillator between the photostrip sensors. The DOI measurement results and the GEANT4 simulation results were compared.