ABSTRACT
Acknowledgements ........................................................................................................................ 31
Note ................................................................................................................................................ 31
Notes on the contributor ................................................................................................................ 32
References ....................................................................................................................................... 32
2.1 Introduction
X-ray crystal structure analysis, and its development, was instigated 100 years ago. The nature of X-rays as waves or corpuscles was a controversy and the thinking on the nature of the electron distributions in an atom was before quantum mechanics. The structures of molecules were undetermined. William Henry Bragg (WHB; 1862-1942) and William Lawrence Bragg (WLB; 18901971), father and son, played the pivotal roles at Leeds University and Cambridge University, in pioneering X-ray crystal structure analysis through 1912-1914, interrupted by the eruption of World War I (WWI) in Europe in August 1914. The Braggs had promptly built upon the rst ‘X-ray diffraction from a crystal’ set of experiments undertaken in Munich by Max von Laue, Walter Friedrich and Paul Knipping, with key roles by Paul Ewald and Arnold Sommerfeld in early 1912. This proved conclusively that X-rays as waves were diffracted by the crystal as a 3-D diffraction grating. Today, we refer to the number of X-ray photons per second incident onto our crystal and our crystal diffracts the X-rays, now as waves. We live with ‘wave-particle duality’ as a common place. Strong evidence for X-rays as waves came from Charles Glover Barkla’s research at Liverpool University through the 1900s on the polarization of X-rays. There were direct clashes in the science literature of the time involving Barkla at Liverpool and WHB, then at Adelaide University, Australia, as he, unlike Barkla, was convinced that X-rays were corpuscular by nature. Nobel Prizes in Physics were awarded to Laue (1914), both the Braggs (1915) and Barkla (1917). The X-ray spectroscopy of the elements by Henry (‘Harry’) Moseley in Manchester was tragically ended when Moseley, by then at the war front in Gallipoli, was killed in 1915. WHB and Earnest1 Rutherford were regularly in touch by correspondence. This commenced when WHB was in Adelaide and Rutherford was in Canada. Their friendship continued when they were both in the North of England, WHB in Leeds and Rutherford in Manchester. WHB also served as External Examiner for Manchester University Physics at Rutherford’s invitation. C.G. Darwin, also in Manchester Physics, grandson of Charles Darwin, derived a key equation for the diffraction of X-rays by a crystal (in 1914).
