A scanning CCD detector for powder diffraction measurements

Several different approaches have traditionally been used for detection of X-ray powder diffraction patterns, including area detectors, point detectors and position-sensitive detectors. Each has advantages. This paper discusses use of a low-cost CCD detector attached to a diffractometer arm, where line-by-line readout of the CCD is coupled to continuous motion of the arm. When this type of detector is used and where X-ray optics are employed to focus the source image onto the detector plane both high-resolution and rapid measurements can be performed, with data collection over a complete 2θ range. This is particularly advantageous for synchrotron applications but valuable also for Guinier diffractometer laboratory instruments. Peak resolutions are shown to be moderately better than what can be obtained with a position-sensitive detector and significantly better than with an area detector. Many samples have intrinsically broadened peak shapes for which little improvement in data quality could be obtained with an analyzer-crystal detector. With comparable numbers of modules, these CCD data collection speeds can be close to those with position-sensitive detectors, but without the low-angle asymmetry seen in the latter.