X-rays have wavelengths short enough to match the spacing between atoms. The Braggs noticed that X-rays passing through a crystal are diffracted and become intense at certain angles. By organizing these conditions they derived the famous Bragg’s Law (nλ = 2d sinθ). Using that law, scientists can calculate the plane spacing d from the angles of intense diffraction peaks and thus determine lattice constants. Their work laid the foundation of modern materials science, helping in mineralogy, metallurgy, drug crystal identification, and even semiconductor design.

In their experiments, the Braggs used single crystals such as quartz and NaCl and analyzed Debye-ring patterns recorded on photographic plates. Bragg’s Law not only gives the interplanar spacing d but, combined with intensity calculations, allows one to obtain the structure factor F(hkl) and thus to infer atomic positions and species. This idea, later augmented by Fourier synthesis and Patterson methods, evolved into full three-dimensional structure determination. X-ray crystallography has since been applied to proteins and DNA, revolutionizing life sciences. Modern synchrotron radiation and XFEL sources push Bragg’s principle to extreme precision, enabling femtosecond time-resolved studies.

Using an ionization tube to generate continuous X-ray spectra, the Braggs systematized the indexing of (hkl) planes by comparing Laue and reflection geometries. Their methodology foreshadowed Friedel’s Law and the phase problem, later influencing the introduction of B-factors and anomalous dispersion techniques. They also proposed absorption corrections in the long-wavelength regime and the heavy-atom method, enabling precise bond-length determination in crystallochemistry. The resolved rock-salt and zinc-blende structures remain benchmark data for phonon dispersion and electronic band-structure calculations in solid-state physics.