Bragg equation

If X-rays of wavelength λ are incident on a crystal, diffracted beams of maximum intensity occur in only those directions in which constructive interfeence takes place between the X-rays scattered by successive layers of atomic planes. If d is the interplanar spacing, the Bragg equation nλ=2dsin θ gives the condition for these diffracted beams; θ is the angle between the incident and diffracted beams and the planes, and n is an integer. Also applied to electron, neutron, and proton diffraction.