Polycell: the elementary detection unit of the ISGRI CdTe gamma-ray camera

A basic component called Polycell has been developed for the ISGRI CdTe gam ma -ray camera of the IBIS telescope on board the INTEGRAL satellite. This imager is an assembly of 16384 CdTe detectors (4 x 4 mm large, 2 mm thick) operating at room temperature. ISGRI covers the lower part (20 keV-l MeV) o f the IBIS energy range (20 keV-10 MeV). Detectors are arranged 4 x 4 on Po lycells, where they are connected to their front-end electronics. The front -end electronics is based on radiation tolerant 4-channel analog-digital AS ICs. The ASICs contain a low-noise charge-sensitive preamplifier (160e(-) r ms; 1 pF load) and a pulse rise-time measurement in addition to the standar d pulse-height measurement. This permits to compute a charge loss correctio n based on the charge drift time. The digital part includes the internal ac quisition timing sequence as well as the dialogue with external electronics . After a description of the front-end electronics, we will present the imp rovements made on the new and final version of this hybrid mini CdTe gamma -ray cameras. In conclusion, we will present the spectometric performance o btained owing to this modular device. A spectral resolution around 7% at 12 2keV is obtained with this last generation of ASICs. (C) 2001 Elsevier Scie nce B.V. All rights reserved.