The mini-calorimeter for the AGILE satellite

AGILE is a small space mission of the Italian Space Agency (ASI) devoted to observations for astrophysics in the gamma-ray energy range 30 MeV-50 GeV with a simultaneous window in the X-ray band 10 keV-40 keV. AGILE payload is made of a tungsten-silicon tracker, a CsI mini-calorimeter for the high energy band and a silicon based X-ray detector (SuperAgile); an anticoincidence system carries out background rejection. In the gamma-ray's band the satellite will have a field of view of about 1/5 of the sky, with angular resolution of a few arc-minutes and good timing resolution. For the high energy AGILE detection principle is based on the pair production process that arises from the interaction between photons and the tungsten layers above the silicon tracker. The silicon tracker is designed to determine the direction of the incoming radiation, while the mini-calorimeter evaluates the energy of the interacting photons and particles. For the detection of transients and gamma-ray burst events, the mini-calorimeter will also work as a stand-alone gamma-ray detector, with no imaging capabilities, covering the energy range 250 keV-250 MeV. The mini-calorimeter is made of an array of position sensitive CsI(Tl) scintillator bars with photodiode read-out. The characteristics of its detector elements and the front end electronics signal processing allow a moderate position reconstruction of the detected event. In this paper a description of the mini-calorimeter is reported as well as a summary of performances reached with the pre-flight instrument models already built and tested.