You may recall the Bragg law from your high school physics
giving the scattering condition for
a wave of wavelength against a series of
lattice planes with lattice spacing , rotated the angle
off the lattice plane normal. is an integer giving the spectral
order of the scattered wave. In neutron science one often refers to
the scattering vector, of a given reflection, where
This gives us the scattering vector formulation of the Bragg law
The Bragg law / scattering condition is illustrated in Figure 1.
Illustration of the Bragg Law.
Most of the neutron processes we will study in this paper are elastic,
meaning that the wavelength of the neutron is unaltered by the process.
Peter Kjær Willendrup