Development And Application Of A New Cosmic Ray Muon Imaging System Based On Plastic Scintillators

Cosmic ray muons(CRM)are natural rays with a wide energy range and strong penetration power.Based on the intensity attenuation of CRM passing through the material,it can realize the imaging of the internal structure of large targets.By using the angular scattering characteristics when they interaction with matter,CRM can realize the discrimination of substances with different atomic numbers.In recent years,the research in CRM imaging technology has made significant progress due to the rapid development of ray detection and computer technology.Domestic and foreign researchers have utilized this technology to conduct deeply research in the fields of imaging the internal structure of volcanoes,scientific and technological archaeology,mineral exploration,industrial production and customs inspection.During the development of domestic muon detector systems,there are problems such as difficulty in purchasing key components and foreign monopoly of technical solutions.To address the above problems,this paper aims to develop a new CRM imaging system based on plastic scintillators,and to conduct research on the detection unit treatment process,system structure design,acquisition system development,and imaging system co-commissioning,performance testing and field experiments.The main research contents and conclusion of this paper are as follows:1.The processing technology and performance of triangular plastic scintillator(TPS)based basic detection unit were investigated.A series of tests were conducted on the influence factors including the surface roughness of the TPS,the reflector layer materials and the photoelectron transfer units,and a solution was determined for the roughness parameters of TPS after polishing,the Enhanced Specular Reflector(ESR)material and the Silicon Photomultipliers(Si PM)single-ended readout.Based on the coincidence measurements of two adjacent detection units,energy spectra as well as correlations were analyzed,these results proved the feasibility for muon position reconstruction by using this scheme.2.The single detector and customized acquisition system were developed,and the key parameters of the detector were tested.The single-layer detector was assembled using TPS basic detector units,and co-commissioned with customized electronic acquisition system.We obtained the single layer detection efficiency of about 98%,the position resolution is about 2.5 mm.The plan of the detectors rotating to different zenith angles and measured the corresponding muon azimuthal counts distribution,verified the consistency of the data at different rotation angles.3.Numerical simulation study on the performance of muon imaging detection system.In the Geant4 framework,simulations of 4-layer and 8-layer detectors were implemented to investigate the factors affecting the detector performance.In the simulations,different position points obtained by using different variables such as muon deposition energy and photoelectron quantity inside the TPS were calculated and compared with the real position points and verified that the position resolution can be characterized using the residual distribution of the fitted and calculated positions.The detectors with different rotation angles were simulated,the results is similar to the experiment ones.The consistency of the measured data of detectors at different rotation angles was verified in the simulation.4.The CRM imaging prototype LUMIS(Lanzhou University Muon Imaging System)which based on the principle of angular scattering was developed.This prototype accomplished the discrimination of different materials and rapid detection function of high Z material.And the feasibility of the technical route of this prototype for application in customs inspection field was verified.Eight detector layers were used in prototype,the coincidence of multi-layer panel to screening muon events.A data acquisition software was developed,which not only controls the data acquisition system,but also has functions such as real-time energy spectrum display,muon track display,online imaging and high Z material alarm.In terms of performance,the angular resolution of LUMIS is about 8.73 mrad at a layer spacing of 40.5 cm.In terms of imaging,the imaging of different combinations of lead bricks was realized based on the Point of Closest Approach(Po CA)algorithm,and the imaging results are basically consistent with the lead bricks profile.Considering the demand of rapid monitoring in customs,the fast alarm algorithm for high Z material was developed by using the method of Scattering Density Estimation(SDE),and the accuracy of judgment was over80% after 2 min measurement.5.The CRM imaging prototype CORMIS(Cosmic Ray Muon Imaging System)which based on the principle of intensity attenuation was developed.CORMIS has 4layers of detector panels,and it has the functions of shock resistance,dustproof,waterproof and angle adjustment to ensure the stable operation of the detector system in outdoor.A remote monitoring and control platform was developed to realize remote real-time control and data synchronization of the system.Field experiments were conducted at the Xi’an city wall.The experimental results presented two low-density zones inside the Horse Face No.58,which basically matched with the actual situation.We completed the first archaeological scenario application of CRM imaging technology in China.This successful application of muon imaging technology on the Xi’an city wall provides a new option for Chinese nondestructive detection of large relics.