X-ray crystal structure analysis and Manchester: from W. L. Bragg to the present day
Professor John R. Helliwell
Professor of Structural Chemistry at the University of Manchester
As part of the 150th anniversary celebrations of the University of Manchester, the Department of Physics and Astronomy organised a special lecture, delivered by Professor J. R. Helliwell, reviewing Lawrence Bragg's association with the university and the many consequent contributions to X-ray crystallography. A notable feature of this lecture was the live demonstrations and experiments illustrating some of the scientific principles discussed.
Helliwell, J. R. (2009). J. Appl. Cryst. 42, 365, doi: 10.1107/S0021889809002775
- Demonstration 1: simulation of powder diffraction pattern (3 min 20 sec)
- Demonstration 2: phases of reflections in crystallography via a 'viewgraphs' Fourier analysis simulator (3 min 40 sec)
- Demonstration 3: microwave analogue of diffraction (3 min 05 sec)
- Demonstration 4: double refraction in calcite (4 min 06 sec)
- Complete lecture (46 min 36 sec)
This is a home-made apparatus involving a 2-D grid/mesh in a holder that allows transmission of a laser beam thus giving a 2D red-laser array of spots; a motorised fan belt rotates the holder thus giving a powder pattern of rings. The adjustment of the speed of the motor allows the transition between spots and rings to be readily seen by the audience. The grid is represented by a pair of 35mm projection slides each holding an optical diffraction grating purchased from a physics teaching supplier. In this Public Lecture the usual dimming of lights was needed and there is a large distance between the rotating gratings and the projection onto the Lecture theatre side wall. The video cameraman does capture the rings to 2D pattern of spots nicely. The sharpness of the 'powder' rings in the video is not as good as the live demonstration.