A method for detailed simulations of neutron diffraction from imperfect crystals

An upgraded version of the McStas Monochromator-curved module is presented. The new component, called Monochromator-reflect, is based on the use of input files for interpolating the neutron reflection and transmission probabilities according to the theoretical reflectivity of the crystal. These probabilities depend on the energy and angle at the crystal surface and also on the crystal mosaicity, geometry, material scattering cross-section, attenuation coefficient, and Bragg planes. We present details of the algorithm and definitions which are essential for a correct use of the module and show the improvements that it offers.