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Laue diffraction at Daresbury

Laue patterns can be recorded at the Daresbury Synchrotron Facility in the UK with exposure times of 0.1 s, and comparatively short times between successive exposures. The patterns can now be processed quickly, efficiently, and accurately to yield several thousand reflective intensities per pattern. The crystallographic community should give serious thought to time-resolved (or other) experiments which make use of these properties.

Participants at a user group meeting, May 11, described (i) the recording of Laue diffraction patterns on image plates, Mar and molecular dynamics, and subsequent processing, and (ii) steps towards rationalization and automation of the main stages in processing. Other recent developments include the evaluation of intensities for reflections which are components of multiple spots, evaluation of unit cell edges from Laue diffraction patterns, and the proper handling of anomalous dispersion contributions in refinements with Laue data.

A Laue diffraction image can now be processed off-line with the Daresbury Laue Software Suite in a few hours. One image can yield intensities for 1/4 to 3/4 of the unique reflections, depending on crystal symmetry and orientation. The Daresbury Lab. has two workstations capable of recording Laue diffraction patterns, for macromolecular crystals or crystals with smaller unit cells. Crystal quality must be good, since the shape of Laue spots is very sensitive to crystal mosaic spread. For any time-resolved experiment it will be important to consider both initial and final crystal quality, as well as time scale, and if possible a method of initiating change uniformly through the crystal. Equipment for controlled heating or cooling of the crystal is available.

M. Harding
Liverpool University, UK
P. Lindley
DRAL Daresbury Lab., UK