Characterization and modelling of germanium assembled crystals for the diffraction of thermal neutrons

Two assembled germanium crystals, produced for use as neutron monochromators, are characterized by means of neutron and X-ray diffraction. The neutron and synchrotron experimental data (reflectivity profiles and topographs) are compared with calculations based on analytical models and Monte Carlo simulations. Our results show the limits of the standard theories and indicate that full Monte Carlo simulations can be a valid tool for interpreting real crystal reflectivities.