Background rejection for the IBIS telescope based on Compton kinematics: experimental tests and Monte Carlo simulations

IBIS (Imager on Board the Integral Satellite) is dedicated to fine imaging in the gamma-ray energy range. The imaging performances are achieved using a coded mask aperture system in conjunction with a position sensitive detector made of two layers. This multilayer structure of position sensitive detectors allows the application of Compton kinematics for background rejection. In order to determine the efficacy of this method, a reduced scale prototype of the instrument has been developed. The detection apparatus is composed by two scintillation matrices of 5×5 elements in the same configuration of IBIS. The upper layer pixel size is 13×13×3 mm whereas the lower layer pixel size is 13×13×30 mm. An hybrid technology electronics has been setup for signals shaping and discrimination, moreover a custom software package has been developed for system calibration and data analysis. The equipment has been tested at different energies by employing radioactive sources. The results are presented and compared, when possible, with Monte Carlo simulations