The scattering of electrons, Xrays and neutrons by crystals can
be described as a reflection of the beams at planes of atoms (lattice
planes), independent of the actual physical reason causing the diffraction
event.
If
the incident plane wave hits the crystal at an arbitrary angle,
the interference of the reflected waves can be either destructive
or constructive.
Destructive
interference of reflected waves (in the two reflected waves, maximum
and minimum of the respective wave amplitude are superimposed).
Constructive
Interference of reflected waves (reflected waves in phase, i.e.,
maxima are superimposed).
To
obtain constructive interference, the path difference between the
two incident and the scattered waves, which is 2dsinΘ, has
to be a multiple of the wavelength λ. For this case, the Bragg equation gives the relation between interplanar distance d and diffraction
angle Θ:
nλ
= 2dsinΘ
