Editing Diffraction (section)

==Bragg diffraction==
{{further|Bragg diffraction}}
[[Image:X-ray diffraction pattern 3clpro.jpg|thumb|Following [[Bragg's law]], each dot (or ''reflection'') in this diffraction pattern forms from the constructive interference of X-rays passing through a crystal. The data can be used to determine the crystal's atomic structure.]]
Diffraction from a large three-dimensional periodic structure such as many thousands of atoms in a crystal is called [[Bragg diffraction]].
It is similar to what occurs when waves are scattered from a [[diffraction grating]]. Bragg diffraction is a consequence of interference between waves reflecting from many different crystal planes.
The condition of constructive interference is given by ''Bragg's law'':
<math display="block"> m \lambda = 2 d \sin \theta ,</math>
where <math>\lambda</math> is the wavelength, <math>d</math> is the distance between crystal planes, <math>\theta</math> is the angle of the diffracted wave, and <math>m</math> is an integer known as the ''order'' of the diffracted beam.

Bragg diffraction may be carried out using either electromagnetic radiation of very short wavelength like [[X-ray crystallography|X-rays]] or matter waves like [[Neutron diffraction|neutrons]] (and [[electron diffraction|electrons]]) whose wavelength is on the order of (or much smaller than) the atomic spacing.<ref name=JMC>John M. Cowley (1975) ''Diffraction physics'' (North-Holland, Amsterdam) {{ISBN|0-444-10791-6}}</ref> The pattern produced gives information of the separations of crystallographic planes <math>d</math>, allowing one to deduce the crystal structure.

For completeness, Bragg diffraction is a limit for a large number of atoms with X-rays or neutrons, and is rarely valid for [[electron diffraction]] or with solid particles in the size range of less than 50 nanometers.<ref name=JMC/>