Experiment and MCNP simulation of a portable tagged neutron inspection system for detection of explosives in a concrete wall

摘要

The Tagged Neutron Method (TNM) widely used in recent years has been applied to detect explosives to fight against terrorism. Because of the existence of a high-density (about 2.5 g/cm(3)) dry concrete wall, neutrons are moderated and gamma-ray are attenuated and absorbed, which causes great interference to the detection of hidden explosives. A movable device has been designed for detection of explosive embedded in a concrete wall by using TNM technique. The experimental set-up was modeled and optimized with the MCNP5 Monte Carlo code. The gamma-ray energy spectrum of graphite sample was firstly collected to calibrate the detection system and verify the validity of the MCNP5 model. Then gamma-ray energy spectra of different samples under different situation are accumulated and compared with the simulation results. The samples of TNT and ammonium nitrate surrogate were placed behind a concrete wall with thickness of 10 cm, 15 cm and 20 cm, respectively. The comparison of the MCNP simulation results with experiment is in a good agreement. The results obtained provide a good reference for the subsequent data acquisition and analysis by using this model.