THE CIEMAT-PSD GAMMA-CAMERA PROTOTYPE RESULTS OF THE TESTS IN A CONTROLLED INSTALLATION

A camera for imaging gamma-ray sources with the characteristics required in nuclear power plants applications has been developed. These requirements refer mainly to portability, small size, compactness and high hardness to the radiation damage of the instrument, goals that can be achieved by using a device based on mercuric iodide (HgI2) detector arrays. This semiconductor is able to work at room temperature without the necessity of cooling, being in addition extremely hardened to high radiation doses. Moreover, its high stopping power makes possible the fabrication of small and efficient detectors. As an example of the equipments that can be constructed based on this material, a Position Sensitive Detector (PSD) consisting of an array of 10 x 10 pixels of 0.8 x 0.8 mm2 has been prepared in our laboratory, together with the front electronics associated to each pixel. The use of a Modified Uniformly Redundant Array (MURA) as focusing element has demonstrated to have excellent properties for the image reconstruction. A coded aperture mask of this type in its square 5 x 5 no-two-hole-touching configuration perfectly matches the detector geometry. The distance mask-detector has been left variable between approximately 7 and approximately 20 cm, that allows one to modify the angular field of view depending on the application. We briefly describe the technical characteristics of the prototype and its imaging capability, presenting the results of several tests done in a controlled radioactive installation. The precision in the positioning of radioactive sources of medium and high energy (Cs-137 and Co-60) and the ability to discriminate separated sources in the field of view are commented.