Monte Carlo simulations of parasitic and multiple reflections in elastically bent perfect single-crystals

A new model including reflections on multiple diffracting planes has been developed and implemented within the neutron Monte Carlo ray-tracing code of the RESTRAX simulation package to describe the diffraction and transmission properties of elastically bent perfect crystals. The new code provides a quantitative prediction of the intensity of parasitic reflections and of the Renninger effect, both of which can significantly modify the intensity of primary reflections and increase the attenuation of a neutron beam traversing a bent perfect crystal. Experimentally observed multiple reflection (MR) effects have been compared with simulated data, the results prove that the new code can predict neutron transport in bent perfect crystals more realistically. Consequently, the MR effects can be considered in the design of neutron monochromators and analysers, which is of particular importance for complex multianalyser systems, where the neutron beam may have to pass through a thick layer of silicon crystal blades.