On the calculation of the differential cross section for scattering of neutrons on crystals

Automatic translation: Every crystal can be built up by repeatedly placing a unit cell next to one another in the direction of the crystal axes, so that a crystal has spatial translational symmetry. The unit cell determines the structure of the crystal; it is spanned by the three basis vectors of the crystal lattice a₁, a₂, a₃, which determine the direction of the crystal axes and whose value is equal to the lattice spacing in the direction of the axis. In general, the unit cell contains r atoms; if it contains only one atom (r=1), then a Bravais lattice is present. There are fourteen different Bravais lattices with different symmetry properties.