The Lonsdale Lecture
The Lonsdale Lecture
The Bragg Lecture
The Hodgkin Lecture and Prize
Kathleen Lonsdale's X-ray studies of diamonds were marked by originality and insight, as was typical of her work. Two lines of experimentation she pursued, photography of the anomalous spike diffuse reflexions and of divergent-beam (Kossel) diffraction patterns, are still under productive development. Other avenues for improved experimentation on diamond have opened up since her lifetime, most notably the use of synchrotron radiation, which has made possible several novel X-ray experiments with diamonds. Important is the topographic approach in understanding the varied diffraction behaviour of diamonds; and scientific benefit accrues from combining this with other spatially sensitive characterization techniques. An early link with optical microscopy showed that the beautiful triangular pyramidal pits, trigons, on diamond octahedral surfaces were natural dislocation etch pits. Correlating both normal and spike reflexion topographs with patterns of optical absorption and cathodoluminescence emission gives data on size and number density of the platelet defects that generate the spikes. X-ray and cathodoluminescence topography complement each other in growth-sector mapping in natural and synthetic diamonds, the X-rays revealing growth-sectorial dependence of lattice defect content, and, via synchrotron X-ray double-crystal topography, of lattice parameter also. Dynamical diffraction phenomena are well demonstrated by the more perfect diamonds; for example, a new manifestation of coherent n-beam diffraction was recently encountered during experiments with a modern version of Lonsdale's divergent-beam technique. (Top of this page).
Sir Gordon Cox died in June 1996 at the age of 90. His crystallographic career lasted from 1927, when he joined Sir William Braggs group at the Royal Institution, to 1960 when he left the University of Leeds to become Secretary of the Agricultural Research Council. In the years just after the end of World War II, Leeds was a hive of crystallographic activity. Besides Cox's large group in Chemistry, there were W. T. Astbury in Biomolecular Structure, G. W. Brindley in Physics and H. J. Woods in Textiles. I arrived in Leeds in 1946 just in time for the post-Congress Symposium of, what may be called, the zeroth Congress of the International Union of Crystallography.
I will discuss some key events in the progress of X-ray structure analysis between 1912 and the present day, but with particular emphasis on those between 1927 and 1960. In 1927 two-dimensional Fourier syntheses had yet to be applied in structure analysis. By 1960 electronic computers were no longer novel. In 1997 we are in an era of synchrotrons and nanosecond time-resolved protein crystallography.
Topics to be mentioned will include:
The Dorothy Hodgkin Prize has been awarded to Professor Michael Woolfson who will deliver the following lecture:
Early structure solutions of simple materials depended on crude trial-and-error methods. The introduction of the Patterson function enabled larger structures to be solved although success often depended on individual insights. The process of solving small-to-medium-size structures was automated by the development of direct methods while, in parallel, the multiple-isomorphous-replacement method led to spectacular progress in protein crystallography. The availability of synchrotron sources together with very sophisticated instrumentation for data collection is making multiple-wavelength anomalous scattering an increasingly-used technique for solving proteins. Current attempts to solve proteins by ab initio methods have so far met with limited success and the theoretical reasons for this wil be discussed. (Top of this page).
