Cadmium telluride (CdTe) constitutes an unique material for X-ray imaging, due to its outstanding properties: room temperature operation, high atomic numbers giving high photoelectric absorption properties, long term stability under irradiation. This paper deals with a procedure we have developed for the use of CdTe detectors in imaging purposes. For demonstration purpose, a 64 linear array has been realized, all detectors being biased at the same voltage. Each pixel is equivalent to a capacitance and a resistance in parallel. The loaded capacitance is disconnected just before irradiation by the X-rays by means of a MOS switching transistor. The detector's equivalent capacitance discharges under irradiation trough the parallel resistance by an amount directly proportional to the charges deposited in the detector, i.e. to the received radiation. In order to measure the corresponding charges, the capacitances of all pixels are successfully loaded for a short time, by switching on a shift register. Each charging current generates between the terminals of a common resistor, a voltage pulse proportional to the beam absorbed. This approach offers several advantages, in particular, to correct the dispersion introduced by differences in detectors, as well as by electronic circuits. Furthermore, it facilitates the use of a dummy line in order to reduce the dark current and parasitic commutation signals. Images of phantoms exposed to the X-ray beam have been visualized with success by means of this system.
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