The calibration and environmental testing of the Engineering Module of GLAST CsI calorimeter

GLAST is the next generation space based gamma ray telescope in the photon energy range 30 MeV - 300 GeV, planned to be launched by NASA in 2006. For photon energy measurements it will use a CsI crystal calorimeter made of 16 identical modules. The Engineering Module (EM) is the first full scale prototype built with the same technology as flight modules to verify the design and technological choices before starting calorimeter production. The module contains 96 CsI crystals, supported by carbon fiber composite structure and read out with silicon PIN photodiodes from both ends. In this paper we report the results of EM calibration using cosmic muons and charge injection during environmental tests. The EM showed stable functioning in the required temperature range from -30°C to +50°C during 6 months of continuous testing and with vibration amplitudes significantly higher than expected during launch. None of 96 crystals experienced mechanical or optical degradation after vibration and 7 thermal-vacuum cycles between -30°C and +50°C. The longitudinal position measurement using light asymmetry from two ends of each crystal provides the position resolution of ∼6-10 mm (2-3% of crystal length) for cosmic muons. The production of flight modules will start in late 2003.