The basic component of the ISGRI CdTe gamma-ray camera for space telescopeIBIS on board the INTEGRAL satellite

The gamma-ray imager telescope IBIS, on board the INTEGRAL satellite, featu res a coded mask aperture and two detector arrays. The first detector array (ISGRI) is an assembly of 16 384 CdTe detectors (4 x 4 mm(2) large, 2 mm t hick) operating at room temperature under 100 V bias. ISGRI covers the lowe r part (20 keV-1 MeV) of the IBIS energy range (20 keV-10 MeV). The polycel l is the basic component of the ISGRI detector array. It is made of 16 CdTe pixels and their front-end electronics. In order to improve the response o f the instrument, a charge loss correction based on the charge-drift time i s necessary. Therefore, the front-end electronics performs the rise-time me asurement in addition to the standard pulse height measure. On the other ha nd, the necessarily tight packaging and the limited available power require s the use of ASICs. These 4-channel analog-digital ASICs should be radiatio n resistant either through the use of a latch up free technology or by appl ying an appropriate layout design. The optimal operating temperature (aroun d 0 degrees C)is ensured under vacuum conditions by radiative cooling. This paper describes the ISGRI design with particular emphasis bn the ASICs and polycells, and reports preliminary performance measurements. (C) 1999 Else vier Science B.V. All rights reserved.