Time dependent neutron detector response simulation for 252Cf

Liquid scintillator detectors are valuable for detection of special nuclear material since they are capable of detecting both neutrons and gamma rays. Furthermore, scintillators can also provide energy information which can help in identification and characterization of the source. In order to deign scintillation based measurement systems appropriate simulation tools are needed. MCNPX-PoliMi is capable of simulating scintillator detector response, however, simulations have traditionally been run in analog mode which leads to longer computation times. In this paper nonanalog MCNPX-PoliMi mode which uses variance reduction techniques is applied and tested. The nonanalog MCNPX-PoliMi simulation test case uses source biasing variance reduction technique to efficiently simulate pulse height distribution and then time-of-flight for a heavily shielded case with a 252Cf source. Neutron time-of-flight measurements are essential to nonproliferation and safeguards efforts to identify and characterize special nuclear material. The resulting simulation is marked by an improvement in the figure of merit (FOM) by a factor of 3.4.