A spaceborne CsI (Tl) calorimeter for cosmic gamma-rays

Features of an instrument capable of measuring accurately cosmic gamma rays in the gigaelectronvolt energy range are discussed. The main component of this instrument is an electromagnetic calorimeter based on rods of CsI(Tl). The expected energy resolution is about 1% at 3 GeV. The use of such a calorimeter in a spaceborne experiment poses some technical problems. The temperature variation of the scintillation light yield must be accurately known in order to correct the data. The temperature dependence using cosmic ray muons and various radioactive sources is reported. The calibration of individual rods is crucial to achieving the desired resolution. Various methods of performing calibration in space, such as radioactive sources and cosmic rays, are discussed and it is concluded that a calibration procedure utilizing cosmic rays is feasible. Space experiments require stable low-power electronics. Readout electronics are presented, and estimates of noise and rates are given