THE X-RAY RESPONSE OF CDZNTE DETECTORS TO BE USED AS FUTURE SPECTROSCOPIC DETECTORS FOR X-RAY ASTRONOMY

The next generation of X-ray astrophysics missions may well extend the energy range beyond the current limit of about 10 keV studied by the existing X-ray Astrophysics space missions such as ASCA or future miss ions such as AXAF and XMM to be launched in the next few years. To add ress with a high degree of sensitivity the astrophysical problems asso ciated with X-ray emission in the X-ray band from 0.2 to 100 keV a sig nificant extension of the capabilities of focusing X-ray optics and im aging broad band hard X-ray detectors will be required. Future mission s such as INTEGRAL, BASIS and EXIST will make use of CdZnTe or CdTe de tectors for imaging spectroscopy down to about 5 keV with a spectral r esolution between 3% and 7% at 100 keV, This is about a factor of 10 a way from what is theoretically possible and mainly caused by the poor crystal quality. In this paper experimental results on the study of th e X-ray response of CdZnTe detectors are presented. The detector respo nse to photons with energies between 1 and 5 keV has been investigated using synchrotron radiation and a preliminary model to describe the d etector response developed. The limitations on the energy resolution, due to incomplete charge collection and spatial non-uniformities, are presented based on the detailed mapping of the energy response of a de tector exposed to highly monochromatised synchrotron radiation. At hig her energies results have been obtained using a Am-241 radioactive sou rce and an electron cyclotron resonance source so as to establish the detector performance and overall response to medium- and higher-energy X-ray photons up to 60 keV. Based on these results the performance of the detectors are compared with Si(Li) and HPGe solid-state detectors . (C) 1998 Elsevier Science B.V. All rights reserved.