Simulation And Experimental Research On The Detection System Of Explosives In Package

It is an important topic for anti-terrorist activities in various countries to detect the explosives hidden in packages rapidly,accurately and effectively.Prompt Gamma Neutron Activation Analysis(PGNAA)is a non-destructive and multi-element nuclear analysis technique that has been widely used in various fields such as mining,medicine,coal quality analysis,and explosives detection.PGNAA is one of the effective techniques for the determination of various sample elements,which can measure the materials with a quality as low as 10~-66 g order of magnitude.Explosives are mainly composed of H,C,O,and N elements,and their elemental concentrations are one of the characteristics that distinguish them from organic materials.PGNAA technology can obtain the content of the main elements C,N and O of the measured object by detecting the prompt gamma rays.The gamma rays are generated by inelastic scattering between neutrons and measured objects.So PGNAA can be used to identify the explosives and organics accurately.The main work in this research is to simulate an explosives detection system based on the PGNAA technology using MCNP5 code.The preliminary design of the explosive detection system was conducted through the theoretical analysis,MCNP simulation and experimental comparison in this paper.The main contents in this study include:1.A movable device used for the detection of explosives hidden inside a package was simulated using MCNP5 code.The neutron source,the gamma detector type,the shielding material between the neutron source and gamma detector and its effective thickness were selected using MCNP5 code.The position of the gamma detector was optimized as well.2.The ammonium nitrate and TNT simulants were simulated using MCNP5.The simulated spectra were compared with the experimental spectra.There is a difference between the experimental and MCNP simulations.Most of the peak values of the simulation were higher than experimental data.This bias is mainly due to systematic errors,the accuracy of nuclear data for producing gamma rays,and modeling and simulation methods.In the future,we will use the explosives detection system and its related electronic equipment for further quantitative measurements to check the causes of this difference.(3)We measured the performance of the explosive detection through experiments.The 300g ammonium nitrate,TNT simulant and powdered milk samples were detected with a neutron generator.The hidden explosives can be detected successfully by this system.Due to the application of sequential analysis,the longest detection time of the system is 10 minutes.The system can reduce the strong gamma ray background interference generated by the fast neutrons and the material around the detected material effectively with the tagged neutron method,and can improve the signal to noise ratio 200-300 times.The device can be used to detect the explosives hidden inside the package,and provide support for explosives detection research.