Optimization Simulations of Micro-Layer Geometries with 10B/ZnO for Neutron Detection

Abstract

Detection of fast neutrons is of utmost importance in many scenarios including calibration of neutron sources, neutron imaging and detection of special nuclear materials (SNM) [1], [2]. Neutron detection frequently relies on converting neutrons to charged particles via elastic scattering or neutron capture. The resulting charged particles interact with the surrounding atoms through Coulomb interactions and deposit their energies in the medium. In this work, efficiency of micro-layered scintillating neutron detectors is investigated with extensive Geant4 simulations. Micro-layer geometries can improve the neutron detection efficiency while decreasing the gamma sensitivity. The proposed detection module consists of neutron capture layers made of boron metal enriched to 95% in 10B, scintillating crystals (ZnO) covering each 10B layer from both sides for light production, and neutron moderators placed between individual 10B/ZnO sandwiches to thermalize fast neutrons. The moderator must be optically transparent so that the light created in the scintillators can travel to photosensors without any significant attenuation. Polyethylene is chosen as the moderator in this work due to its low-Z content and optically transparent nature. Photosensors are placed at four corners of the detector module to detect optical photons. After optimizing the detector components, neutron detection efficiency for 1 MeV neutrons was estimated to be 6.8%, 3.2%, and 1.5% for 5, 10, and 20 photon thresholds at the photosensors, respectively. Finally, the gamma sensitivity of the detector module was estimated to be in the range of 10−3-10−4 for 1 MeV gamma rays.