The CsI(Tl) Detector Element (CDE) is the unit of detection of the calorimeter subsystem of the Large Area Telescope (LAT) of the GLAST satellite [1], which will be launched in September 2006. The LAT consists of 4 x 4 identical towers, each one including a strip silicon tracker on the top and a CsI(Tl) calorimeter on the bottom. A segmented plastic scintillator anticoincidence detector surrounds the 16 towers. The calorimeter modules, 8 layers of 12 CDEs each, have a hodoscope’s shape to allow the measurement of the gamma-ray direction.
The CDE main characteristics are its Light Yield (L.Y.: number of electron given by the PIN photodiodes by deposited MeV in the crystal), the energy resolution and the tapering, ratio of left/right signals used for the determination of the crossing position of the particle in the crystal.
The CDE have to operate in space at about –10°C. We will describe the CDE, the optimization of its main parameter, the L.Y., and finally its variation with temperature.
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