A Century Plus of X-rays

The Imperatives in Atomic Structure Analyses: Lessons from Three- Dimensional Diffraction Gratings, Specular Reflection and Quasi- Crystals

“…The last problem surfaced with Dan Shechtman's discovery of quasi-crystals [3,4]; systems in which the diffraction pattern defy Bravais classification or the assignment of Miller indices. It exposed a severe inadequacy in Laue-Bragg's famously successful technique in crystallography [5][6][7][8][9]. Furthermore new advances such as high intensity coherent radiation beams, ultrashort exposure and extremely fast detectors, coupled with the desire for atomic resolution in real time, demands a reassessment of the premises of classical crystallography; also it is imperative to find the way to an alternate approach that is indifferent to long-range order and baggage from the associated reciprocal space, leverages the principle of 'reflection-diffraction duality' to embody Bragg's computationally facile top-down approach with Laue's local bottom-up perspective, and (ii) covers a definition of crystal matter that is more inclusive especially the complex regime of partial loosening of order, but not complete disorder.…”

Laue: right or wrong?

“…Besides, Barkla had explicitly listed the characteristic emitters from soft onward to the hardest as Cr, Fe, Co, Ni, Cu, Zn, As, Se, Ag. It is known that right after the spots were observed, using different thickness platelets of aluminum, the experimentalists promptly concluded that the spots arose from the primary incident radiation and not the secondary fluorescence; the post-experiment discordance between Friedrich and Laue over the anticipated role of the secondary radiation ipso facto shows that not all the theoretical ideas about the experiment were clear at the start [6][7][8][9][10][11][12].…”