The Cosmic Ray Muons Tomography System And Image Reconstruction Algorithm Study Based On Monte Carlo Method

Cosmic ray muon imaging is a new non-destructive imaging technique,which utilizes natural cosmic rays and effectively avoids the risk of radiation damage.Natural cosmic rays have strong penetration and are sensitive to materials with high proton number,so they are widely used in many fields and disciplines,such as nuclear safety detection,nuclear facility monitoring,stratigraphic terrain detection and archaeological building detection.However,limited by the low flux of muons,the imperfect imaging algorithm,the high cost of detector system and the constraints of engineering construction and other factors,the existing imaging technology is often unable to obtain high quality reconstructed images in a relatively short time.In order to develop a universal and cost-effective muons imaging system and improve the imaging quality under the premise of a small number of muons,this paper proposes and designs two kinds of detector systems that carry out scattering and transmission imaging mechanisms,and studies the detector structure,system parameters and corresponding imaging algorithms.Based on the complete kernel database of Monte Carlo particle transport software Geant4 and the powerful geometric modeling and processing ability,the simulation research and the development of track reconstruction algorithm for the imaging system of the muon detector such as triangular bar scintillator and wavelength shifting fiber detector system are carried out.Meanwhile,the image reconstruction algorithm is developed and improved based on experimental data of triangular bar scintillator detector.The specific research contents and achievements are as follows:1.In Geant4,CADMesh method was used to construct an imaging system of the plane detector based on triangular bar scintillators with complex geometric structure.Compared with the existing design of a fiber embedded triangular bar scintillator,the system has a better resolution for small area plane detector imaging and reduces the production cost.In the model,the physical processes of optical light photon scintillation,transport and boundary layer effect are completely introduced.Based on the structure characteristics of the triangular bar element,a path reconstruction algorithm of the system is given,and its geometric scale and spatial arrangement are improved by simulation.Finally,the trajectory reconstruction algorithm is used to obtain the incident position of the muons,and the error between the inversion value and the true value is less than 2mm.Based on the imaging system platform built by the team based on the triangular bar plastic scintillator,the position resolution of 2.5mm experimental measurement was obtained.2.Based on the idea of track image reconstruction algorithm and statistic image reconstruction algorithm,a new image reconstruction algorithm named path algorithm is proposed based on Po CA algorithm.Using this algorithm,under the premise of effective events obtained in about 5000 experiments,different graphs can be clearly distinguished.At the same time,in different cases of simulating 1000-30000 effective events,the reconstruction image is constructed with obvious advantages compared with other algorithms.3.In order to further improve the cost performance of the detector,a set of plane muon detector imaging system based on wavelength shifting fiber-scintillator was constructed in Geant4,and the feasibility of this scheme was verified in the simulation.Based on the transverse inhomogeneity of optical yield,a position inversion algorithm based on fitting function,function regression calculation and iteration test is proposed and developed,and angle correction and detector geometric structure adjustment are added.Finally,the position resolution of 0.79 mm is obtained.The path algorithm mentioned above is used to reconstruct the complex spatial stereo model,and the details of the complex model in the reconstructed image are clearly visible.4.Based on the wavelength shifting fiber-scintillator plate muon detector system,a muon detector imaging system is designed by spatial reconstruction of its geometric model.The actual application scenario was modeled and simulated in Geant4.Using the same position inversion algorithm as the fiber-scintillator plane detector,the complete muon track could be obtained in a single detector,and the mineral position set in the stratigraphic standard rock in the simulation could be reversed more accurately.