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

A basic component called Polycell has been developed for the ISGRI CdTe gamma -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) of the IBIS energy range (20 keV-10 MeV). Detectors are arranged 4 x 4 on Polycells, where they are connected to their front-end electronics. The front-end electronics is based on radiation tolerant 4-channel analog-digital ASICs. The ASICs contain a low-noise charge-sensitive preamplifier (160e(-) rms; 1 pF load) and a pulse rise-time measurement in addition to the standard pulse-height measurement. This permits to compute a charge loss correction based on the charge drift time. The digital part includes the internal acquisition timing sequence as well as the dialogue with external electronics. After a description of the front-end electronics, we will present the improvements made on the new and final version of this hybrid mini CdTe gamma -ray cameras. In conclusion, we will present the spectometric performance obtained owing to this modular device. A spectral resolution around 7% at 122keV is obtained with this last generation of ASICs. (C) 2001 Elsevier Science B.V. All rights reserved.