THE CZT X-RAY IMAGER ON AXO C. BUDTZ-JØRGENSEN 1∗ , I. KUVVETLI 1 , N.J. WESTERGAARD 1 , P. JONASSON 1 , V. REGLERO 2 , C. EYLES 3 and T. NEUBERT 4 1 Danish Space Research Institute, Juliane Maries Vej 30, Copenhagen, Denmark 2 University of Valencia, Valencia, Spain 3 University of Birmingham, Birmingham, U.K. 4 Danish Meteoroligical Institute, Lynbyvej 100, Copenhagen, Denmark ∗ Author for correspondence; E-mail: carl@dsri.dk Abstract. DSRI has initiated a development program of CZT X-ray and gamma ray detectors employing strip readout techniques. A dramatic improvement of the energy response was found operating the detectors as so-called drift detectors. For the electronic readout, modern ASIC chips were investigated. Modular design and the low power electronics will make large area detectors using the drift strip method feasible. The performance of a prototype CZT system will be presented and discussed. One such detector system has been proposed for future space missions: The X-Ray Imager (XRI) on the Atmospheric X-ray Observatory (AXO), which is a mission proposed to the Danish Small Satellite Program and is dedicated to observations of X-ray generating processes in the Earth’s atmosphere. Of special interest will be simultaneous optical and X-ray observations of sprites that are flashes appearing directly above an active thunderstorm system. Additional objective is a detailed mapping of the auroral X-ray and optical emission. XRI comprises a coded mask and a 20 cm × 40 cm CZT detector array covering an energy range from 5 to 200 keV. 1. Introduction The potential of X-ray and gamma ray detectors based on heavy element semicon- ductor materials is now recognized within many fields. One of the most promising heavy element semiconductor materials is the CdZnTe (CZT). The principal ad- vantages of the CZT semiconductor material are high quantum efficiency and no requirement for cooling to cryogenic temperatures. These properties make the CZT detector very interesting in relation to space applications and ideally suited for a small satellite. With their superior performance compared to other X-ray de- tectors, these detectors are already employed in various fields such as radiology, high-energy astronomy and materials science. In Denmark, Danish Space Research Institute (DSRI) initiated a program to develop detectors based on CZT in the beginning of 1996. The main motivation at that time was to develop focal plane detectors for the novel type of hard X-ray telescope (Christensen, 1996), which is currently being studied at DSRI. During the year 1997, the CZT detector research at DSRI resulted in a number of methods to improve considerably the spectral resolution. The technique so-called the drift strip Astrophysics and Space Science is the original source of this article. Please cite this article as: Astrophysics and Space Science 276: 281–289, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.