CCD-based detector for protein crystallography with synchrotron X-rays

Abstract

A detector with a 114 mm aperture, based on a charge-coupled device (CCD), has been designed for X-ray diffraction studies in protein crystallography. The detector was tested at the National Synchrotron Light Source with a beam intensity, through a 0.3 mm collimator, of greater than 109 X-ray photons/s. A fiberoptic taper, an image intensifier, and a lens demagnify, intensify, and focus the image onto a CCD having 512×512 pixels. The statistical uncertainty in the detector output was evaluated as a function of conversion gain. From this, a detective quantum efficiency (DQE) of 0.36 was derived. The dynamic range of a 4×4 pixel resolution element, comparable in size to a diffraction peak, was 104. The point-spread function shows FWHM resolution of approximately 1 pixel, where a pixel is 160 μm on the detector face. A data set collected from a chicken egg-white lysozyme crystal, consisting of 495 0.1° frames, was processed by the MADNES data reduction program. The symmetry R-factors for the data were 3.2–3.5%. In a separate experiment a complete lysozyme data set consisting of 45 1° frames was obtained in just 36 s of X-ray exposure. Diffraction images from crystals of the myosin S1 head (a = 275 Å) were also recorded; the Bragg spots, only 5 pixels apart, were separated but not fully resolved. Changes in the detector design that will improve the DQE and spatial resolution are outlined. The overall performance showed that this type of detector is well suited for X-ray scattering investigations with synchrotron sources.