Development of X-ray∕Gamma-ray Imaging Spectrometer with Reach-through APD arrays

It is quite important to obtain wide band spectra of high energy astrophysical phenomena at the same time in order to probe emission processes or structures. Especially observations of transient objects, such as gamma‐ray bursts, expect detectors with wide energy band coverage for the sake of an efficient spectroscopy within limited time windows. An avalanche photo diode (APD) is a compact photon sensor with an internal gain of ∼100. We have developed an X‐ray/gamma‐ray detector using a reach‐through APD (5×5 mm2) optically coupled with a conventional CsI(Tl) scintillator, which covers typically from 1 keV to 1 MeV. Further, we developed a 1‐dimensional array of the 8/16 APDs (net 16×20) mm2) for the purpose of an imaging photon detector combined with coded masks, to be applied in future missions. We present the current status and performances of our hybrid detector using the 8‐channel array.