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Models for ray-tracing simulations of thermal neutrons monochromators

In recent years there has been a continuous interest in applying ray-tracing techniques for simulating the performance of neutron instruments. This technique is well known for other applications dealing with photon beams (visible, IR, UV and X-rays). Several codes have been developed by different groups to either calculate, with high accuracy, some particular optical elements of a neutron instrument, or to give rough estimations of the whole instrument including simple models of the individual elements. Our goal is to create an optimised code for neutron optics using accurate descriptions for each optical element. In this paper we will analyse the existing models for treating mosaic crystals monochromators. We will report on the calculated and measured diffraction properties of mosaic copper and pyrolytic graphite crystals, which are two of the most commonly used neutron monochromators.