Direct Neutron Scattering Observations in BC408 Scintillator, and Comparison to Simulation*

Monte Carlo simulation is important for interpretation of experimental data from fast neutron-scintillator interactions (involving elastic and inelastic scattering from C and H nuclei), especially in experiments requiring multiple neutron detection, such as in studies of neutron-unbound nuclear states above the 2n threshold, owing to the difficulty of distinguishing single and multiple neutron interactions in the detector volume. To test our GEANT4 modeling we transported 16 detectors from MoNA (the Modular Neutron Array at NSCL/MSU), each consisting of a 200x10x10 cm$^3$ bar of organic plastic scintillator BC408 with a PMT fixed to each end, to Los Alamos National Lab.  The detectors were arranged in two different stacking geometries in the 90-m station on LANSCE/WNR flight path 4FP15L and exposed to a tightly-collimated beam of spallation neutrons ranging in energy from 0.5 to 800 MeV. GEANT4 Simulation predictions (using both the GEANT4 physics package as well as MENATE\_R) were compared with scattering observations for 20-200 MeV neutrons.  Simulation was most accurate for events involving the first neutron scatter, but differences (some significant) existed for modeling a neutron scattering multiple times.  Results will be presented.