The Agile Gamma-ray Detector

The gamma-ray detector AGILE, operating in the energy range from 30 MeV to 50 GeV, is composed by a tracking part, a light calorimeter and an anticoincidence system. Here we describe the detector and its capabilities to determine the arrival direction and energy of the detected photons. The AGILE design is derived from a refined study of the GILDA project (Barbiellini et al. 1995, Morselli et al. 1995) that was based on the techniques developed for the Wizard silicon calorimeter, already successful flown in balloon experiments (Golden et al. 1990). Like previous orbiting high-energy gamma-ray telescopes, AGILE relies on the unambiguous identification of the incident gamma-rays by recording the characteristic track signature of the e +-e − that result from pair creation from the incident photons in thin layers of converter material. The trajectories of the pairs, recorded and measured in the tracking section of the detector, give the information on the direction of the incident gamma-rays. A light calorimeter made of 1.5 radiation lengths (X 0) of cesium iodide (CsI) allows to determine the energy of the incident photons. The detector has a height of ∼35 cm, with a 40 × 40 cm 2 area and a total conversion length, for electromagnetic cascades, of ∼2.3 X 0. A schematic view of the AGILE detector is presented in Tavani et al. (1998). The three AGILE components are: i) a tracker: this is the conversion zone. It consists of 12 planes of single sided silicon strips with 204 µm pitch (distance between strips). The strips are implanted on pads of 8 × 8 cm 2. Each pad has a thickness of 380 µm and carries 384 strips. The first ten planes consist of two layers of silicon detectors, with orthogonal strips interspersed with a layer of 0.07 X 0 of tungsten. The last two planes have no tungsten sheets. Each plane reads 3840 strips and the entire tracker consists of 46080 strips. The distance between consecutive planes is 1.6 cm; ii) a light calorimeter: it is made of 1.5 X 0 of CsI and will provide an indication of the photon energy; iii) an anticoincidence system: it consists of 0.5 cm thick plastic scintillator layers surrounding the top and four lateral sides of the silicon tracker. It will be able to significantly reduce the background due to charged particles. ——————————————————————————-(⋆) Adapted from a paper presented at the Conference Dal nano-al Tera-eV: …