Developments of a New 1-Dimensional$gamma$-Ray Position Sensor Using Scintillators Coupled to a Si Strip Detector

In order to operate an “improved” Fourier synthesis imager at higher photon energies than are accessible with solid-state detectors, we developed a new one-dimensional$gamma$-ray position sensor consisting of inorganic scintillators whose light is read out by a silicon strip detector (SSD). The SSD is read out through stripped p-electrodes (DC-coupled, 32 channels at 400$mu$m pitch). The n-side of the SSD does not have a metallic surface, and has a relatively good optical transparancy. A stack of optically isolated thin CsI(Tl) scintillator plates (10 mm$,times,$10 mm in area and 0.3 mm thick) is attached, edge-on, to the n-side of the SSD. When a$gamma$-ray photon hits the stacked scintillator, the generated scintillation light is detected by the SSD, with the signal pulse-height largest in the p-electrode which is just beneath the CsI plate hit by the$gamma$-ray. The 32-channel outputs from the SSD are acquired simultaneously for each event with a low-noise analog ASIC. The$gamma$-ray position can be calculated as a weighted mean of pulse heights. Using this system, we have obtained a position resolution significantly finer than 1 mm for$gamma$-rays with energies greater than$sim500$keV up to$sim$1300 keV.