Imager IBIS

Principal Investigator: Co-Principal Investigators: with collaborating scientific institutes in Italy (IAS Rome, ITESRE Bologna, IFCAI Palermo), France (CEA Saclay), Norway (U Bergen), Germany (U Tuebingen), Spain (U Valencia), USA (NASA/MSFC Huntsville), Poland (Space Research Centre, Warsaw), UK (U Southampton). 
The Imager IBIS (Imager on Board the Integral Satellite) provides diagnostic capabilities of fine imaging (12 arcmin FWHM), source identification and spectral sensitivity to both continuum and broad lines over a broad (15 keV - 10 MeV) energy range. A tungsten coded-aperture mask (located at 3.2 m above the detection plane) is optimised for high angular resolution. As diffraction is negligible at gamma-ray wavelengths, the angular resolution obtainable with a coded mask telescope is limited by the spatial resolution of the detector array. The Imager design takes advantage of this by utilising a detector with a large number of spatially resolved pixels, implemented as physically distinct elements. The detector uses two planes, one 2600 cm^2 front layer of CdTe pixels, each (4x4x2) mm (width x depth x height), and a 3000 cm^2 layer of CsI pixels, each (9x9x30) mm. The CdTe array (ISGRI) and the CsI array (PICsIT) are separated by 90 mm. The detector provides the wide energy range and high sensitivity continuum spectroscopy required for Integral. The division into two layers allows the paths of the photons to be tracked in 3D, as they scatter and interact with more than one element. Events can be categorised and the signal to noise ratio improved by rejecting those which are unlikely to correspond to real (celestial) photons, e.g. towards the high end of the energy range. The aperture is restricted by a lead shielding tube and shielded in all other directions by an active BGO scintillator veto system. 
Further details of the current design can be accessed here:

Imager IBIS WWW home page IAS Rome, Italy
Imager IBIS WWW in Bologna TeSRE Bologna, Italy
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