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A joint neutron-gamma detection system was designed using a two-stage Monte Carlo simulation approach to identify large-volume ammonium nitrate from buried landmines. To investigate possible spectral anomalies associated with the presence of landmines, the phase space shell concept was used to study the response of a LaBr3 scintillator gamma-ray detector to photons from neutron activation of specific chemical elements in the explosive and soil, as well as the response of a He-3 thermal neutron counter to backscattered thermal neutrons. At a neutron emission energy of 5 MeV, the soil-specific gamma-ray peak energies of 4.94 MeV (Al), 7.65 MeV (Al), and 8.45 MeV (Si) showed a decrease in peak area, which increased as the detection system approached the landmine. The ammonium nitrate-specific peak at 10.82 MeV (N) occurred only in the presence of a landmine. The difference in count rate recorded by the He-3 counter between soil without explosive and soil with explosive increased as the detector system approached the landmine. The combined information from the gamma and neutron detectors provides a good fingerprint for the presence of a suspected landmine. The source shielding, featuring a spherical multi-layered graphite, polyethylene, and lead shielding, improved the useful gamma ray intensity and the registered difference in thermal neutron count rate and reduced the background gamma radiation and direct neutrons reaching the same detectors. [ABSTRACT FROM AUTHOR]

In this paper, MCNP5 code is used to establish a landmine clearance system based on pulse fast thermal neutron method. The system prototype is modeled based on the NG-9 D-T neutron generator, which is independently developed by Northeast Normal University. Gamma rays produced by fast neutron inelastic scattering and thermal neutron capture are used to identify suspicious areas. The neutron flux passing through landmine cell before and after adding neutron reflector into initial detection system is studied. The simulation results show that the addition of a neutron reflection layer hardly improves the flux of fast neutrons passing through the landmine cell during at pulse width of 10 µs; but the thermal neutron flux through the landmine cell in the pulse interval of 90 µs is significantly increased. Among the several common reflector materials, tungsten (W) and tungsten carbide (WC) materials show better reflection performance. When W and WC are used as reflector materials and the thickness is 6 cm, the thermal neutron flux through the landmine cell is 2.00 and 1.90 times the initial value, respectively. The ratio of the thermal neutron flux in the pulse interval to the fast neutron flux during the emission of the neutron pulse increased to 0.468 and 0.444, respectively, from the initial value of 0.259. Finally, the improved model is used to simulate the landmines hidden in different depths. The results show that using 4.44 MeV and 2.22 MeV peak area counts in the region of interest can identify whether there are explosives in the detection area. [ABSTRACT FROM AUTHOR]