The calibration and environmental testing of the engineering module of GLAST CsI calorimeter

GLAST is the next generation space-based gamma ray telescope for the energy range 30 MeV-300 GeV, to be launched by NASA in 2007. For photon energy measurements it will use a CsI crystal calorimeter made of 16 identical modules. The engineering module (EM) calorimeter 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 a 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 ray muons and charge injection during environmental tests. The EM showed stable functioning in the required temperature range from -30 C to +50 C during six months of continuous testing, including seven thermal vacuum cycles between -30 C and +50 C and vibration testing with amplitudes significantly higher than expected during launch. None of 96 crystals experienced mechanical or optical degradation after the tests. The longitudinal position measurement is accomplished using light asymmetry from two ends of each crystal, providing ∼6--12 mm position resolution (2-4% of crystal length) for cosmic ray muons. The production of flight modules will start in late 2003.