  Neutron transport along guides is governed by the Liouville theorem and the
technology involved has advanced in recent decades. Computer simulations have
proven to be useful tools in the design and conception of neutron guide systems
in facilities. In this study, we use a Monte Carlo method to perform
simulations for an S-shaped neutron guide with different dimensions for a
Small-Angle Neutron Scattering (SANS) instrument, through the MCSTAS software.
A wavelength cutoff is observed and shown to be dependent on the geometrical
parameters of the guide. Results for the neutron flux at sample position are
presented and a greater sensitivity of cutoffs concerning the curvatures of the
guides than to their lengths is noticed. Our results are in agreement with
those obtained from the Acceptance Diagram method and we analyze the beam
divergence behavior along the S-shaped guide.
