Performance of multiple-CCD X-ray detector system at SPring-8 for protein crystallography

The 4 x 4 multiple CCD X-ray detector installed in the beamline 45XU of the SPring-8 facility in Japan was examined by acquiring X-ray diffraction images of lysozyme crystals. The detector system was calibrated at the beamline by observing X-ray images of a flood-field and a mask pattern generated by the synchrotron radiation X-ray beam. It was found in the present work that the quality of the X-ray images observed is limited by an unexpected spike noise, the origin of which was suspected to be the gamma-rays emitted from the radioisotopes remaining in the X-ray scintillating screen. Image analysis carried out with a median filter predicted, however, that the image quality could be as high as designed, once the noise as well as the grain colonization is removed from the screen.