Spots on a Plate: Bragg's Law | Crystallography 2.6

In spring 1912 in Munich, X-rays sent through a copper sulfate crystal left a scatter of sharp spots on a photographic plate. This episode reads that photograph three ways: Laue's rows of atoms, Lawrence Bragg.s planes acting as faint mirrors with the law 2d sin θ = nλ, and Ewald's sphere in reciprocal space, where a reflection happens when a lattice point touches the sphere. The sphere also explains the rotating-crystal, Laue and powder methods, and it predicts copper's peak positions, including one that real copper never shows. Chapters 0:00 Munich, 1912: spots on a plate 1:21 Three readings of one photograph 1:55 Laue: scattering from a row of atoms 3:56 Bragg: planes as faint mirrors 4:20 Deriving Bragg's law 5:51 Bragg reads the zinc blende photographs 6:40 The Ewald sphere in two dimensions 7:40 Why the sphere is Bragg's law 8:29 The sphere in three dimensions 9:27 Three classic methods 10:34 Copper's powder peaks 11:57 Back to Munich 12:35 The peak that is missing Reference: M. Martínez-Ripoll (with the late F. Hernández Cano), Crystallography-Cristalografia, web course (CSIC, CC BY-NC 4.0, https://www.xtal.iqf.csic.es/Cristalo..., and university crystallography and diffraction lecture notes. Historical sources: Laue, Concerning the detection of X-ray interferences, Nobel lecture (1920): https://www.nobelprize.org/uploads/20... · W. L. Bragg, Nobel lecture (1922): https://www.nobelprize.org/uploads/20... · Nobel Prize in Physics 1914 (von Laue): https://www.nobelprize.org/prizes/phy... · Nobel Prize in Physics 1915 (W. H. Bragg and W. L. Bragg): https://www.nobelprize.org/prizes/phy... · Eckert, account of the 1912 Laue experiment (2012): https://www.xtal.iqf.csic.es/Cristalo... Previous episode: 2.5 "The Reciprocal Lattice". Next episode: 2.7 "Missing Reflections". Narration: AI voice (ElevenLabs); music: AI-generated (Lyria) and original synthesized tracks.