Honouring the two Braggs: the first X-ray crystal structure and the first X-ray spectrometer

摘要

In the Centennial celebrations of the birth of X-ray crystal structure analysis, a key feature is to mark the articles which are the first crystal structure analysis studies. This mini review describes the historical development and quotes key statements of W.L. Bragg (WLB) as well as W.H. Bragg (WHB) and the perspectives offered by key players of the time period. The first crystal layout, as stated by WLB, is the face-centred cubic arrangement evident in the Laue Laboratory diffraction photographs recorded from a crystal (of zinc blende) and provided to WHB. The first crystal structure, as stated by WLB, and explicitly remarked upon by P.P. Ewald, as well as WLB's official biographer, D.C. Phillips, is sodium chloride and which was published in June 1913. The use of the X-ray spectrometer of WHB, and the measurements by WHB, at Leeds University, with this device are acknowledged by WLB in his article. This 1913 article also contains numerous raw diffraction data in the form of 'Laue photographs' measured by WLB of NaCl, and most importantly of KCl, in Cambridge. WLB seemed to anticipate the use of these two isomorphous and closely related alkali halide crystal structures in his article of 1912. The X-ray spectrometer as the forerunner of all X-ray diffractometer designs is also a remarkable initiative of WHB.