Crystal quality Laue method

As with neutron powder methods, both monochromatic and time-of-flight (Laue) techniques have been used for single-crystal neutron studies. Such studies are much less numerous, however, as a result of the difficulty of compressing suitably sized (>1 mm ) single-crystal sample to the required pressure while maintaining the crystal quality. The piston cylinder cell design of Me Whan and others [128] has been used at the ILL reactor source for a number of neutron structural studies to... 

The positions of the spots on the film, for both the transmission and the back-reflection method, depend on the orientation of the crystal relative to the incident beam, and the spots themselves become distorted and smeared out if the crystal has been bent or twisted in any way. These facts account for the two main uses of the Laue methods the determination of crystal orientation and the assessment of crystal quality. 

It seems that a substantial part of the radiation damage in proteins and viruses (and some other crystals, too) is a function of time from the first exposure to the beam. The synchrotron Laue method allows complete data recording in a shorter time from first exposure than any other method. Of course, protein crystals differ greatly in their susceptibility to radiation damage. For example, some survive a single exposure while, at the other extreme, cases such as pea lectin can survive many exposures. Indeed, it now seems that many protein crystals (>50%) are able to yield high quality synchrotron Laue diffraction photographs. 

The software required for the quantitative evaluation and wavelength normalisation of Laue data has been successfully developed at Daresbury since the feasibility of recording full white beam Laue patterns from protein crystals was established. The software and the method have been tested using Laue data from crystals of pea lectin. As an example of the statistical quality (to 3 A resolution) the mean fractional change on F between monochromatic and Laue pea lectin data was 11 % and the same quantity between conventional source monochromatic and SR monochromatic pea lectin data is 8% (Helliwell et al., 1986). 

---