Compton Imaging Accuracy Influence Mechanism And Improvement Method

With the increasingly important role of nuclear technology in the national economy and national security,the prevention of nuclear proliferation faces some challenges.Effective ver-ification plays an important role in guaranteeing the parties' performance of their obligations.The verification of nuclear materials,especially nuclear weapons,is a necessary means of main-taining the balance of power and guaranteeing world peace.However,verification techniques used now are limited because not only the complex radiation background,but also certain polit-ical factors have to be considered,which means that the balance between sensitive information and detection accuracy must be considered.Compton Camera,which has a high signal-to-noise ratio and can image the contour of nuclear materials without the inside information,has broad application prospects.The main purpose of this thesis is to understand the imaging theory of Compton Camera in mathematics and physical mechanism,to analyze factors affecting imaging accuracy,to study its imaging performance under different situation,to investigate the properties of Compton cam-eras for wide-range,multi-energy radioactive sources detection under complex background,to propose a phase mechanism suitable for arms control verification scenarios,and to use simu-lation method to evaluate related detection field performance.The ultimate aim is providing technical reserves for defense technology,especially for arms control verification.Firstly,the basic physical principle and imaging algorithm of Compton camera are intro-duced.The effect of detector energy resolution,detector position resolution,Doppler Broad-ening in Compton Scattering and coherent scatter of ? ray on imaging accuracy are studied by combination of theoretical calculation and Monte Carlo simulation.Optimal design criterion for Compton Camera used different scenes are proposed according to these research results,which are used in the following research.Secondly,MC method is used to study the inherent laws in Compton cameras.The opti-mization of first detector material and thickness are done according to these laws.Si is selected as the material of first detector because of its high Compton Scattering ratio and small Doppler Broadening effect.1-5 mm Thickness Si is suitable for camera construction for multi consid-ering of interspace distribution of two interaction,escaping event ratio,and the manufacturing level of DSSD.The proportion of escaping events in ideal situation and the proportion of ideal events in total deposited events are studied.Also the proportion of various events in total de-posited events and their influence on imaging performance are analyzed.Considering real position resolution and energy resolution,energy threshold and position signal screening criteria are established.Due to the lack of depth positioning of the detector,two algorithms namely Average Depth Method and Random Depth Method are proposed to try improving imaging accuracy.These method are based on the distribution rule of ? ray interaction with detector.The results show that compared with conventional Centering Depth Method,the two algorithms improve imaging accuracy obviously when the average depth is smaller than the center of the detector.Besides the Random Depth Method is slightly better than the Average Depth Method when ? energy is highFinally,Steve Fetter Nuclear Warhead Model is used as a multi-energy source to how much high energy gamma ray affecting low energy gamma ray while imaging.Emission ? ray spectrum is studied to obtain original ? proportion,and then EPM was defined according to this spectrum.The model was used to study the effect of high energy ray on low energy ray while imaging multi-energy source.The results show that both the energy and the intensity of ? ray have relation of how much this characteristic ray is affected.The spherical and hemispherical Steve Fetter model is imaged by a step-by-step simulation.The results show for a nuclear warhead with obvious asymmetry and symmetry,Compton Camera can give an asymmetric or symmetric result clearly,without revealing the internal structure.In this paper,the imaging mechanism and imaging algorithm of Compton Camera are sys-tematically studied.Various factors affecting imaging efficiency and accuracy are analyzed by theoretical calculation and Monte Carlo simulation.Average Depth Method and Random Depth Method are proposed which improve the imaging accuracy.The effect of high energy gamma ray on low energy gamma ray imaging while imaging shielded radioactive sources using Comp-ton Camera is evaluated.The performance of Compton Camera for the detection of shielded nuclear materials,especially the detection of material symmetry properties,is evaluated.This study provides technical reserves for arms control verification.