Evaluation of detection efficiency and neutron scattering in NAND detector array: FLUKA simulation and experimental validation

摘要

The light output response and efficiency of 5″ × 5″ BC501A liquid scintillator neutron detectors composing the NAND detector array have been measured by time of flight technique using ~(252)Cf source. Energy dependent detection efficiency was calculated using FLUKA Monte Carlo code and validated by experimental measurement. FLUKA simulation incorporated fission neutron correlation and kinematics of neutron emission from fission source determining the energy distribution of neutrons in the laboratory frame. The intrinsic features of the scintillator were studied by including particle dependent quenching and light output resolution. Comparison of FLUKA simulation of scintillation light produced by neutrons and gamma rays with measurements provided realistic results. The calculated neutron detection efficiency at ～0.5 MeV threshold reproduces the experimental data reasonably well in the studied energy range, 0.5 ＜ E_n ＜ 12 MeV. Neutron scattering from target chamber material in NAND was investigated using FLUKA concluding that the loss in neutron flux due to scattering from the chamber wall is ～ 12%. The scattering amounts to background neutron counts in neighbouring detectors comparable to cross-talk events. The absolute efficiency of the NAND array was estimated to be ～1.40% after taking into consideration the intrinsic efficiency of liquid cells, geometrical efficiency and flux loss due to scattering.