<title>I. A Monte Carlo algorithm for the simulation of Bragg scattering by imperfect crystals; and II. Application to mosaic copper</title>

We present a Monte-Carlo algorithm for the simulation of Bragg diffraction from imperfect crystals that are used for neutron analysers and monochromators. The algorithm is used in ray-tracing simulation of neutron instruments but can also be used for x-rays. This method performs a detailed description of the particle interaction with the microscopic regions composing the crystal. It computes important quantities that cannot be calculated with standard models, as the number of multiple scattering events, and diffraction topographs. We also discuss applications of this method to the analysis of x-ray data from mosaic copper crystals.