Simulation of the AGILE gamma-ray imaging detector performance: part I

We present in this paper the results of a comprehensive GEANT simulation of the Gamma-Ray Imaging Detector (GRID) being developed for the AGILE space astrophysics mission. The GRID is designed to be sensitive in the ~30MeV-50GeV energy range, with excellent imaging and timing capabilities, and with a very large field-of-view (~3sr). In this paper (Paper I) we present the GRID baseline geometry, a model for the charged particle and albedo-photon backgrounds for an equatorial orbit of 550-600km altitude, and the main results of the first level (Level-1 Trigger) on-board data processing. Our simulations show that the GRID Level-1 data processing is expected to be capable of decreasing by a factor of ~20 the charged particle background (from ~2kHz to below 100Hz), and by a factor of ~30 the albedo-photon background. The gamma-ray photon detection efficiency by the imaging GRID is simulated to be particularly efficient, varying between 39% and 17% depending on photon energies and incident directions.