The Lorentz factor for the Laue technique

When the Laue technique is applied to ordinary diffractometer devices and detector systems, problems appear with respect to the Lorentz factor that are unsatisfactorily treated in the literature. A detailed treatment of beam divergence and mosaic spread leads to a derivation of the exact expression for the Lorentz factor for X-ray diffraction with white radiation. This expression differs from the usual formulae if the mosaic spread and beam-divergence angles are of the order of magnitude of the diffraction angle. In addition, the different expressions for the Lorentz factor appearing in the literature are discussed in detail.