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R.P. Johnson, W.B. Atwood, V. Chen, H.A. Hernando, M. Hirayama, W. Kroeger, G. Paliaga, H. Sadrozinski (University of California Santa Cruz), E. Bloom, J. Broeder, B. Feerick, G. Godfrey (Stanford Linear Accelerator Center), T. Kamae (Tokyo University), T. Oshugi (Hiroshima University), GLAST Collaboration
The Gamma-ray Large Area Space Telescope instrument concept is a gamma-ray pair conversion telescope that uses silicon microstrip detector technology to track the electron positron pairs resulting from gamma-ray conversions in thin converter foils and a cesium iodide calorimeter to measure the energy. Silicon strips are a mature, robust technology with an excellent heritage in space science and particle physics. It has many characteristics important for optimal performance of a pair conversion telescope, including high efficiency in thin detector planes, low noise, and excellent resolution and two-track separation. The large size of GLAST and high channel count in the tracker puts demands on the technology to operate at very low power, yet with sufficiently low noise occupancy to allow self triggering. A prototype systems employing custom-built ASIC's has been built and tested that meets the design goal of 200 microwatts per channel power consumption with a noise occupancy of less than one hit per trigger per 10,000 channels. Detailed design of the full-scale tracker is well advanced, with all components prototyped, and a complete 50,000-channel engineering prototype tower module is currently under construction and will be tested in particle beams in late 1999. Results from a 1997 test of prototypes in a tagged photon beam are presented, together with the status of the instrument design and engineering and prototype tower construction.
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