Scattering and multiple scattering in NISP

It is very common to use Monte Carlo integration to estimate multiple scattering corrections in neutron experiments. The neutron instrument simulation package (NISP) includes various sample types and materials, many of which also account for multiple scattering. By combining the simulation of beam optics and multiple scattering, significant correlations are included. This report describes the implementation of multiple scattering in NISP, and shows the cross-section algorithms currently used. Source codes are available. An example of a full multiple scattering simulation is shown.