AbstractRigorous tests of the Monte Carlo transport code MCNP have been performed by measuring the efficiency of a6Li-glass moderating neutron detector using Lucite as the moderator relative to the efficiency of the detector using mineral oil as the moderator, and comparing this with the MCNP predicted value. The tests were done using both252Cf fission-source neutrons and 1.2-MeV neutrons produced by a Van de Graaff accelerator.