A Monte-Carlo study of a 3-D position sensitive detector for gamma-ray astronomy

We present a Monte-Carlo simulation of a prototype of the CsI imager originally designed for the GRASP mission and now adapted for the new gamma-ray satellite experiment INTEGRAL. The imager is based on a two layer CsI(Tl) detector position sensitive in all three dimensions, coupled with a coded aperture mask placed at ∼4 m from the scintillator. The Monte-Carlo code has been written using both the simulation packages GEANT3 and EGS4. As a central theme to this article we present Monte Carlo estimates of three features which are important to the coded aperture imaging process: detection efficiency; detector spatial resolution and the relative response over the entire sensitive area of the imager detection array. The possibility of providing sensitivity to the degree of polarization of the incoming photon beam, through the three-dimensional study of the Compton scattered events, is also treated.