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W. N. Johnson, J. E. Grove (NRL), B. F. Phlips (Geo. Mason Univ.), J. Ampe (Praxis, Inc), S. Singh (NASA/GSFC), E. Ponslet (Hytec, Inc.)
We describe the design, construction and performance of the CsI hodoscopic calorimeter of the GLAST beam test engineering module (BTEM), a full size prototype of one of the 16 towers of the GLAST Large Area Telescope (LAT), approved by NASA to be launched in 2005. The calorimeter is comprised of 80 CsI crystals organized in a hodoscopic arrangement with 8 layers of 10 crystals. The crystals are read out with PIN photodiodes at both ends. Light tapering along the length of the crystals produces an asymmetry in the light measured at the ends. The asymmetry is used for interaction positioning along the length of each crystal. The major design goals included the demonstration of a mechanical design to survive launch into space with minimal passive material, low power electronics with a dynamic range of ~3 x 105, and digital data acquisition with <20 \musec dead time per event. We will describe the design and will give results from the analysis of the beam test in winter 1999/2000 at SLAC, where the BTEM was tested in gamma, positron and hadron beams.
This work was supported by NASA as part of the GLAST Advanced Technology Development program, NASA DPR S-15539-Y.