Saturday, 28 January 2012

100 years since the first single crystal X-ray experiments

100 years since the first single crystal X-ray experiments!!! The year 2012 represents the centennial of the first single crystal X-ray experiments, performed at the Ludwig Maximilian Universität, Munich, Germany, by Paul Knipping and Walter Friedrich under the supervision of Max von Laue. Max von Laue was awarded the Nobel prize in Physics 1914 "for his discovery of the diffraction of X-rays by crystals": "One evening in February 1912, the physicist Peter Paul Ewald sought von Laue's advice about some difficulties he was having with his doctoral thesis on the behaviour of long electromagnetic waves in the hypothetical space lattices of crystals. von Laue couldn't answer Ewald's question, but his mind began to wander. Suddenly, a connection clicked in his mind. If diffraction and interference occurs when the wavelength of light is a similar size to the width of the slit of an optical grating, and if X-rays were indeed waves that have a wavelength at least ten thousand times shorter than visible light, then in theory the spaces between the atoms in a crystal might be just the right size to diffract X-rays. If all this were true, von Laue thought, a beam of X-rays passing through a crystal will be diffracted, forming a characteristic interference pattern of bright spots on a photographic plate.
Sommerfeld was sceptical when von Laue approached him with this idea. He doubted the experiment would work, and besides he needed his assistants for other assignments. Nevertheless, Sommerfeld was generous enough to give von Laue the go ahead to carry out the study. von Laue designed an experiment in which he placed a copper sulphate crystal between an X-ray tube and a photographic plate. His assistants, Walter Friedrich and Paul Knipping, carried out the experiment. After a few initial failures, they met with success on 23 April, 1912. X-rays passing through the crystal formed the pattern of bright spots that proved the hypothesis was correct."

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