Low energy neutron propagation in MCNPX and GEANT4
  Simulations of neutron background from rock for underground experiments are presented. Neutron propagation through two types of rock, lead and hydrocarbon material is discussed. The results show a reasonably good agreement between GEANT4, MCNPX and GEANT3 in transporting low-energy neutrons. 
R. Lemrani, M. Robinson, V. A. Kudryavtsev, M. De Jesus, G. Gerbier,   N. J. C. Spooner