Physical Crystallography Group

Philips Physical Crystallography Award 1996

The winner of the Philips Award for 1996 was Dr. C. C. Wilson of ISIS. Dr. Wilson, otherwise known as Chick to his many friends and colleagues, is a well-known figure in neutron diffraction in the UK and abroad. He received his prize primarily for his sterling work on the single-crystal diffraction station (SXD) at ISIS and particularly for his novel time-efficient data collection methods. Chick has effectively employed an area detector for time-of-flight (tof) Laue diffraction. Although the solution of static structures is less favourable on such an instrument, the system is ideal for monitoring changes in structure and he has recently developed this capability for the study of structural phase transitions and hydrogen-atom disorder in low-symmetry molecular crystals.

Materials that he has studied include PbHAsO4 and benzoic acid. In the latter case, a full set of data for refinement was collected at 175 K in only one day with subsequent runs at 100 K, 50 K and 20 K taking a further three days. These are rapid experiments by single-crystal neutron standards. From the data, Chick has been able to follow the hydrogen atom ordering in benzoic acid. Linear behaviour of lnK vs 1/T (K being the ratio of the occurrence of the two possible configurations) was found down to 50 K, allowing the energy difference between the two configurations to be determined. However, the 20 K point lies off the line, indicating that there is more interesting physics in the system. Data between 50K and 20K and below 10 K are required to complete the study and should be obtained soon.

Dr Wilson has made a further innovative contribution to the tof Laue method by the employment of the multi-crystal data collection technique which involves the exposure of several crystals of the substance under investigation at once. The crystals, which are oriented randomly with respect to each other, are mounted in a glass capillary and are separated from each other by glass wool. One-crystal, two-crystal and three-crystal exposures are taken and processed together to provide a fuller data set than that obtained from a single crystal alone. The time for collecting a full data set can be reduced substantially by using this multi-crystal technique. In addition, the technique also allows more flexibility in the use of sample environment, since fewer crystal rotations are required.

Chick gave a clear and interesting presentation of his research work to the assembled audience at the Tuesday morning session of the British Crystallographic Association Spring Meeting in Cambridge. Chick has been a familiar figure at BCA meetings over the past years and has picked up poster prizes, I recall, on more than one occasion. Even though he frequently confesses to being a chemical crystallographer when pressed, I think that all in the audience would agree that he is a worthy winner of the Physical Crystallography award for 1996.

Pam Thomas, June 1996

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