PICsIT detector for γ-ray astronomy: pixels qualification campaign

Position sensitive detectors coupled to coded masks are used for imaging in high energy astronomy. PICsIT is the γ-ray position sensitive detector of the IBIS telescope to be flown onboard the INTEGRAL satellite in 2001. PICsIT detector functionalities and scientific performances as a whole are described in details elsewhere in this Conference (Labanti et al. (Nucl. Instr. and Meth. A, this conference)). In this work, we present the aim, methodology, and results of the tests and calibrations performed on the first qualification lot of 136 PICsIT pixels carried out at SCIONIX laboratories in The Netherlands, in April 1999. Before being accepted for PICsIT, each detection unit has in fact to be fully characterized in terms of energy resolution and lower energy threshold. The principal aim of PICsIT pixel qualification campaign described in this work has been to measure the key parameters of each CsI(Tl)+photodiode detection unit: CsI(Tl) crystals light output, gain variation with temperature, energy resolution degradation due to scintillation light production and collection, inhomogeneity in the crystal, and the variation of these quantities after a thermo-vacuum stress treatment.