NEW DEVELOPMENT OF HGI2 X-RAY AND SOFT GAMMA-RAY DETECTOR FOR SYNCHROTRON RADIATION RESEARCH AND DOSIMETRY APPLICATIONS

This paper describes recent progress in the development of HgI2 as an X-ray and soft gamma-ray detector for synchrotron radiation research and dosimetry application. The high efficiency of the detector depends on the photon absorption inside the crystal and on the free charge carrier collection at the electrodes under the influence of the applied bias. The dominant mechanisms determining the collection of charge carriers, produced by incident ionizing radiations, are the trapping-detrapping phenomena and the carrier drift mobility. The relative role of these two mechanisms, photon absorption and carrier collection, is related to the thickness of the HgI2 crystal. The analysis of trapping-detrapping phenomena, which are strongly related to the detector fabrication process, are discussed and the measurement of the carrier drift mobility, cutting the crystal parallel and perpendicular to the c-axis, is presented. The results of energy resolution measurements obtained exposing HgI2 detector prototypes of different thickness and with the electrodes realized by evaporizing different metals on the crystal surface, to X- and gamma-radiactive source, are presented and discussed. We have found, using a 900-mu-m-thick detector with 500 angstrom Pd electrodes evaporated on both surfaces (sandwich arrangement), an energy resolution equal to 600 eV at 5.9 keV X-ray (Mn-K-alpha) and 10.5 keV at 122 keV gamma-ray (Co-57).