Integral imager: Prototype scientific performances

The Imager proposed for the gamma-ray satellite project INTEGRAL is based on a multilayer two-dimensional array of CsI(TI) elements viewed by Si photodiodes. The total active area is ≈2500 cm2. The operative energy interval ranges from 0.05 to 10 MeV. A prototype version of this instrument, ready to be tested on a ballon-borne experiment, has been realized. In this article the expected performances of the instrument are presented, toghether with the first calibration results of the prototype.