X-ray diffraction topography (XRT) and reciprocal space mapping (RSM) are used to study the perfection of single crystals. They allow in a complementary way obtaining local and integral information about their defects and defect structures, or their mosaic spread. Modern synchrotron radiation sources in combination with modern detectors, this lead among others to higher resolution, shorter adjustment and exposure times, and to the possibility to record weak reflections or to work under weak beam conditions. Dedicated instruments permit combining several experimental methods within one experimental set-up - e.g. XRT, with RSM, and data collection for structure analysis. This allows relating the defect structure of crystals with a) growth conditions and processes as well as the effects of crystal treatment, and b) the resulting properties (diffraction conditions, physical properties). This will be demonstrated characterizing the perfection of protein crystals. Hen egg white lysozyme was chosen as model protein owing to its high resistance to radiation damage, feasibility of growing large rather perfect crystals and easy handling. The crystals were oriented and its reflections were indexed using a MAR image plate detector. In that way we could work with selected and well-indexed reflections. A comparison of results of double and triple crystal topography, high-resolution diffraction and reciprocal space mapping allowed obtaining complementary information about the defect structure of the crystals. The crystals revealed a number of features quite well known in solution or hydrothermal grown inorganic crystals: dislocations, growth bands and growth sector boundaries. Dislocations in the <110> sectors have been characterised as edge dislocations with Burgers vector parallel to the c axis. They were distinguishable only under weak beam conditions. The existence of spiral growth steps (observed by surface techniques) is consistent with the presence of edge dislocations.

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1. X-ray imaging