Organic scintillators response function modeling for Monte Carlo simulation of Time-of-Flight measurements.

In neutron Time-of-Flight (TOF) measurements performed with fast organic scintillation detectors, both pulse arrival time and amplitude are relevant. Monte Carlo simulation can be used to calculate the time-energy dependant neutron flux at the detector position. To convert the flux into a pulse height spectrum, one must calculate the detector response function for mono-energetic neutrons. MCNP can be used to design TOF systems, but standard MCNP versions cannot reliably calculate the energy deposited by fast neutrons in the detector since multiple scattering effects must be taken into account in an analog way, the individual recoil particles energy deposit being summed with the appropriate scintillation efficiency. In this paper, the energy response function of 2″×2″ and 5″×5″ liquid scintillation BC-501 A (Bicron) detectors to fast neutrons ranging from 20 keV to 5.0 MeV is computed with GEANT4 to be coupled with MCNPX through the "MCNP Output Data Analysis" software developed under ROOT (Carasco, 2010).