= X-ray diffraction
{c}
<X-ray diffraction> is the angular redistribution of <X-ray> <wave intensity> through <wave interference> between scattered waves. In a <crystal structure>, repeated <lattice translations> select discrete outgoing directions by the <Laue equations>. A <photographic plate> can therefore turn invisible atomic periodicity into a visible constellation of spots. Their geometry constrains the <Bravais lattice> and its orientation; their <wave intensities> also depend on the <crystal basis structure factor>. Determining atomic positions belongs to <X-ray crystallography> and requires more information than recognizing a spot pattern.
The <Laue X-ray diffraction experiment of 1912> established this phenomenon experimentally. The <Laue method> uses a fixed <crystal structure> with a range of incident <wavelengths>; the <Bragg crystal reflection experiment of 1913> instead measured angularly resolved signals with a moving detector. These are different ways of finding the same <coherent elastic scattering> directions.
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