THE POINT-SPREAD FUNCTION OF X-RAY IMAGE-INTENSIFIERS CCD-CAMERA AND IMAGING-PLATE SYSTEMS IN CRYSTALLOGRAPHY - ASSESSMENT AND CONSEQUENCES FOR THE DYNAMIC-RANGE

The point-spread functions (PSFs) of two X-ray CCD detectors and two imaging-plate (IF) scanners were compared using the monochromatic beam of the Materials Science beamline of the ESRF. The CCD detectors were a commercial medical type X-ray image intensifier (XRII) for energies above 20 keV and a tube with a beryllium window especially designed for the 5-50 keV range, optically coupled to a high-resolution cooled charge-coupled-device (CCD) camera. The IP scanners were the Fuji BAS2000 and the Molecular Dynamics PhosphorImager 400E, with plates from Fuji and Kodak. The PSFs were recorded using a 30 x 30 mu m pinhole at energies from 8 to 41 keV under normal and highly saturated conditions. Special care was taken in the study of PSF wings. Dynamic-range capabilities in the presence of PSF bleeding were also measured using a standard X-ray generator. The Fuji and MD IP scanners give very similar PSFs when used with Fuji plates [circa 130 mu m full width at half-maximum (FWHM), 1100 mu m at 0.1% of peak maximum]. The Kodak plates showed a broader PSF than the Fuji plates, one which also increases with X-ray energy. The standard XRII/CCD gave the coarsest PSF (circa 4000 mu m at 0.1% of peak maximum), whereas the finest PSF was recorded with the beryllium XRII/CCD used in magnified mode (900 mu m at 0.1%). The best dynamic range was obtained with the XRII/CCDs; the lowest with the Fuji scanner.