Study On The 14MeV Fast Neutron Imaging With Geant4

In the context of international instability, forbidden objects are more easily obtained by criminals, which will cause great harm to personal safety and property safety. The frequently-used security detection equipment has played an important role in security work, but there is still some false or missing detection. Fast neutron imaging method is a feasible choice to minimize such situations. This work includes two parts:Firstly,Geant4, an open international Monte-Carlo program package, was used to physically model bombarding the test substances(HEU, Al and PE) using security screening machine X rays as well as 14 Me V fast neutrons. The simulation data were analyzed and processed using Root tools. X rays and 14 Me V fast neutrons were used to produce 2D transmission image of the test substances, with the results suggesting that:14Me V fast neutrons have a better maximum detection capability(8cm-thick lead box) than X rays(0.4~0.55mm), and additionally the former are able to qualitatively differentiate the density of test substances;the position, time, and other data of the gamma rays generated by the test substance(n, ?) reaction induced by 14 Me V fast neutrons were used in combination with the incidence angle of the neutrons while reconstructing the test substance 3D images, and the results indicate: the gamma rays, produced by the interaction of 14 Me V fast neutrons and the test substance, provides a means of detecting hidden objects as well as reconstructing 2D or 3D image of the objects. Also, the relative contrast degree of the reconstructed images may help qualitatively discriminate what kind of material a test substance is. The simulation test results demonstrate that fast neutron imaging comes with excellent spatial resolution and moderate substance identification capability, and it may therefore help us resolve the technical challenge of detecting hidden contraband substances.Secondly,By using the internationally applied software, GEANT4 Monte Carlo, the simulation study on the physical process of forbidden objects detection by 14 Me V fast neutron activation analysis method and characteristic ? ray detection by Yap(CE) scintillator detector and on the image reconstruction method was conducted, and ROOT toolkit was used to process and analyze the data. In order to distinguish forbidden objects from everyday objects, the energy spectrum distribution of characteristic ? rays generated by hitting forbidden objects and everyday objects with fast neutrons was simulated and a qualitative and quantitative analysis of the energy spectrum of characteristic ? rays was made. And the ? ray flux was calculated, with the detector positioned at different angles and various distances. Taking into consideration the photon transmitting course in the Yap(CE) scintillator,the optimized parameters of the best detection position for the detector were obtained; namely, the optimal angle is 180 degrees, and the optimal distance is 15 cm.Last but not least,The achievements in related researches not only are expected to lay a foundation for researches on 14 Me V fast neutron imaging technology and its application., but also The relevant results can be used as theoretical evidences for the physical and engineering design of the movable fast-neutron detection system for forbidden objects.