EVALUATING X-RAY-DETECTORS FOR RADIOGRAPHIC APPLICATIONS - A COMPARISON OF ZNSCDS-AG WITH GD2O2S-TB AND Y2O2S-TB SCREENS

ZnSCdS:Ag was evaluated as a radiographic image receptor and was compa red with Gd2O2:Tb and Y2O2S:Tb phosphors often used in radiography. Th e evaluation of a radiographic receptor was modelled as a three-step p rocess: (i) determination of light output intensity as related to the input radiation dose, (ii) determination of visible light characterist ics with respect to radiographic optical detectors, and (iii) determin ation of image information transfer efficiency. The light intensity em itted per unit of x-ray exposure rate was measured and theoretically c alculated for laboratory prepared screens with coating thicknesses fro m 20 to 220 mg cm(-2) and tube voltages from 50 to 250 kVp. ZnSCdS:Ag light intensity was higher than that of Gd2O2S:Tb or Y2O2S:Tb for tube voltages less than 70 and 80 kVp respectively. ZnSCdS:Ag displayed th e highest x-ray to light conversion efficiency (0.207) and had optical properties close to those of Gd2O2S:Tb and Y2O2S:Tb, and its emission spectrum was well matched to optical detectors. The image information transfer properties described by the modulation transfer function, th e quantum noise transfer function, and the detective quantum efficienc y were calculated for both general radiographic and mammographic condi tions and were found to be intermediate between those of Gd2O2S:Tb and Y2O2S:Tb screens. Conclusively, ZnSCdS:Ag is an efficient phosphor we ll suited to radiography.