Supermirror physics with event biasing in MCNP6

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Beamlines for cold and thermal neutrons instruments use low-roughness multilayered films called supermirrors, which aim to reflect neutrons below a critical angle. Calculations related to the design of these guides are often made with optics codes like Monte Carlo Simulation of Triple Axis Spectrometers (http://www.mcstas.org/, [1]), sometimes in combination with particle transport physics codes like Monte Carlo-N Particle (MCNP, Goorley et al., 2012) or Geant4 (Agostinelli et al., 2003) [2], and more recently, supermirrors physics implemented in MCNPX (Gallmeier et al., 2009). We have ported this functionality into MCNP6, and also expanded its capabilities by implementing deterministic transport through the guides, and allowing the use of Deterministic Transports Spheres (DXTRAN) (Booth, 2008) [3]. The results have been compared to existing work with positive results.