Simulation Study Of Neutron CT Imaging Technology For FNMIS

As we all know,there are roughly three main forms or means of carrying out scientific and technical research,namely basic research,simulation research,and experimental research.Simulation research is an indispensable technical method or development stage for basic research to enter or move towards applied basic research.Due to the particularity of the strong radioactivity of nuclear materials or nuclear components for nuclear material identification technology research based on nuclear radiation theory,and the confidentiality of using nuclear materials or nuclear components for nuclear arms control verification and identification technology research,The Monte Carlo(MC)method for nuclear signal analysis and processing of nuclear materials or components is the most commonly used research tool at home and abroad in the field of nuclear science and technology.This paper relies on the National Natural Science Foundation project"Basic Research on the Application of Compressed Sensing Theory of ²⁵²Cf Source Driven Fission Neutron Pulse Signal"(No.11605017),using MC method,based on Nuclear Material Identification System(NMIS)and Fieldable nuclear material identification System(FNMIS),carrying out neutron imaging simulation test research,with which neutron imaging information is used to analyze and identify the properties of nuclear materials.The research content of the thesis mainly includes:(1)The measurement principle and analysis method of time-spectrum signal NMIS driven by ²⁵²Cf source are studied.A three-channel NMIS simulation system was constructed to simulate the neutron transport process of nuclear material fission driven by ²⁵²Cf neutrons.The neutron pulse time domain signals of each channel were obtained.The time domain of the tested material was extracted through correlation analysis Feature tags are used to identify the properties of nuclear materials.(2)The performance of different types of nuclear materials and their different states based on NMIS was studied.Carried out comparative measurement and analysis of fissile materials(HEU,DU)and non-fissile materials(Fe,Pb,polyethylene);carried out research on enrichment properties,geometric properties of fissile materials and shielding effect of fissile materials.The results show that the NMIS based on the ²⁵²Cf source-driven structure can effectively divide fission and non-fissile materials and identify the enrichment properties of fissile materials.At the same time,the research also shows that the physical measurement conditions such as the geometry of the material and the presence or absence of the shielding layer have a greater influence on the measurement results.Therefore,under the condition that the measurement conditions are unknown,the reliability of the NMIS recognition result is not high,and it is easy to cause misjudgment.(3)Researched the theory of direct neutron imaging,including Digital Radiography(DR)imaging and Computed Tomography(CT)imaging.When direct neutrons pass through an object,they obey the Lambert-Beer law,and the attenuation coefficient distribution of the object can be obtained by the difference between the incident intensity and the exit intensity of the neutron.DR imaging obtains the projection of the object in the direction of the parallel neutron beam,and CT imaging obtains a tomographic image of the neutron beam passing through the object.Studies have shown that direct neutron DR imaging and CT imaging can obtain the internal structure information of the nuclear component to be tested to a certain extent,which can provide a reliable reference value for attribute recognition.(4)The theory and reconstruction algorithm of parallel collimated neutron CT imaging for identifying fissile materials are studied.In order to directly distinguish fissile nuclides and stable nuclides of nuclear material on the image,according to the principle of nuclear material induced fission reaction,an appropriate"fission time window"is selected,and induced neutrons are obtained and used for CT imaging.Studies have shown that induced neutron CT can spatially locate fissile nuclides and display fission nuclide enrichment information.The introduction of DR or CT image information can practically improve the performance of NMIS,and the effect is remarkable.In particular,induced neutron CT can accurately reconstruct the spatial distribution and concentration information of fissile elements of the tested nuclear material,and can play an important role in future-oriented nuclear arms control verification and nuclear proliferation prevention applications.(5)Summarized the main research work and achievements of the paper,and also looked forward to the future research work.