| Prompt gamma neutron activation analysis(PGNAA)technology adopts transmission or reflection method for material detection and has the characteristics of non-destructive,non-contact,online,and fast The domestic PGNAA technology has been successfully applied in the cement and coal fields,while the PGNAA technology in the sintering field is monopolized by the United States.In this work,PGNAA technology is used as the detection method,and Monte Carlo simulation technology is applied to optimize and upgrade the detection device.The modified algorithm is used to eliminate the gamma self shielding and neutron self absorption effects of the sintered mixture itself.Finally,the real-time and online detection of the element content of the sintering mixture is realized.The main research contents of this thesis are as follows:(1)The prompt gamma neutron activation analysis experiment and data processing process are systematically studied.PGNAA online element analysis system consists of neutron generating unit,neutron slowing unit,radiation shielding unit,gamma detector unit,energy spectrum acquisition unit and spectrum processing unit.The PGNAA detection system selected in this paper uses 252Cf spontaneous fission neutron source as the neutron generation unit.The system uses a combination of graphite and measured material as the neutron moderator unit,and uses a composite polyethylene material with a de1sity of 1.3085g/cm3 and 45%B4C as the neutron shield material,and the NaI scintillator detector as the Gamma detector unit The digital multi-channel energy spectrometer based on trapezoidal shaping algorithm is used as the energy spectrum acquisition unit of the detection system.The weighted least squares method is used as the energy spectrum solution algorithm.(2)Aiming at the optimization of the gamma-ray detection efficiency of this equipment,a Monte Carlo simulation tool-GTFADE was developed.GTFADE software greatly shortens the simulation time of gamma detection efficiency by simplifying the interaction between gamma rays and matter.Different models are used to test the simulation software.The simulation results of GTFADE are highly consistent with the simulation results of MCNP and the simulation efficiency is higher,which proves the accuracy and superiority of the calculation results of the GTFADE simulation software.The input file of GTFADE software is compatible with MCNP input file,and the input format of gamma ray simulation position is the same as that of fmesh card.In order to combine with the simulation data of neutron transport,the output file format of GTFADE is the same as that of meshtal.(3)The activation reaction efficiency and the gamma-ray detection efficiency are comprehensively considered,and the device structure is optimized for the element analysis of the sintered mixture.Because the sintered material and the cement raw material are quite different in physics and chemistry,the detection device of the cement analyzer cannot be directly applied to the detection field of the sintered material,and the device needs to be re-optimized.The neutron moderator,the activation region and the detector are interrelated,and the optimal structure cannot be obtained by considering any part in isolation.This work first considers each part individually,then splices it into a basic structure,and then optimizes and improves this basic structure.The existing PGNAA detection device is optimized and upgraded.After optimization,the space gamma detection efficiency is increased by 44%,the thermal neutron distribution probability is increased by 13.24%,and the comprehensive detection efficiency is increased by 71.52%.(4)The measurement accuracy of the device is improved by correcting the measurement nonlinearity caused by sample gamma and neutron self-absorption.The optimized device is used for the sintering material detection experiment.Since the main element in the sintering material is iron,and the iron element itself is a gamma-ray shielding material,the sintering material has a serious gamma ray self-absorption phenomenon.In the experiment,the gamma ray attenuation detection device is added to modify the gamma ray energy spectrum.After the correction,the linear R2 of total iron is increased from 0.637 to 0.935,the linear R2 of calcium oxide is increased from 0.961 to 0.995,and the linear R2 of silicon dioxide is increased from 0.97 to 0.994.The main content element of sintering mixture is iron and contains a small amount of chlorine,which leads to its neutron self absorption characteristics.In this paper,the correction calculation of neutron self absorption for iron is carried out,and the linearity R2 of total iron is improved to 0.998.(5)The analyzer has been applied in two sintering plants in China.In the actual dynamic detection process,the analyzer has ideal trend prediction effect on total iron,calcium oxide and silicon dioxide of sinter products.After the application of the analyzer in A sintering plant,the basicity stability rate increased by 3.98%,and that in B sintering plant increased by 3.96%,which brings nearly ten million RMB economic benefits to the plant every year.The innovations of this thesis are as follows:(1)Aiming at the optimization of the gamma-ray detection efficiency of this equipment,a Monte Carlo simulation tool-GTFADE was developed.GTFADE software greatly shortens the simulation time of gamma detection efficiency by simplifying the interaction between gamma rays and matter,and realizes the simulation of gamma detection efficiency in space matrix.(2)According to the characteristics of the sintered mixture,the existing PGNAA detection device is optimized.After optimization,the space gamma detection efficiency of the device has increased by 44%,the thermal neutron distribution probability has increased by 13.24%,and the overall detection efficiency has increased by 71.52%.(3)Aiming at the phenomenon of gamma ray self attenuation of sintered mixture,the characteristic gamma ray energy spectrum recovery technology is designed.The linearity R2 of total iron is increased from 0.637 to 0.935,the linearity R2 of calcium oxide is increased from 0.961 to 0.995,and that of silica is increased from 0.97 to 0.994.In view of the phenomenon of neutron self absorption of sintering material,a neutron self absorption correction algorithm is designed,and the linearity R2 of all iron is raised to 0.998. |
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