Theoretical And Experimental Studies Of The Fission Products For Neutron-induced Fission Of Heavy Actinide

In recent years,with the rapid development of the economy,the energy demand is increasing in China.The rapid consumption of the energy leads to some serious environmental problems.For this reason,the Chinese government has proposed a development plan for a high-efficiency and clean fission nuclear energy system to alleviate the problems of energy shortage and environmental degradation.The design and construction of fission nuclear energy utilization systems require complete and accurate fission nuclear data.However,there are still many missing neutron-induced actinide fission nuclei in databases,which restrict the development of new nuclear energy systems.Therefore,there is a need to research neutron-induced actinide fission theory and nuclear data calculation methods,experimental measurement techniques of fission nuclear data,etc.,for the construction of a fission nuclear database.According to the construction needs of the fission nuclear database,this thesis mainly focuses on the Monte Carlo-based theoretical calculation method of neutron-induced actinide fission products,the development of a TFGIC detector for fission product measurement,and the experimental measurement method of fission products.The main research contents and conclusions of this thesis are:1.Optimization of the neutron-induced actinide fission model and calculation of fission productsThe relationship between the peak-to-valley ratio of mass distribution and incident neutron energy and the excitation function TKE_prerecommended by Madland were introduced into the original Geant4 fission Model,G4Para Fission Model.The optimized model Modified Model was proposed.The Modified Model was used to calculate the properties of neutron-induced fission products of typical actinide nuclei.The main researches as follows:1)The fission fragment yields of typical neutron-induced fission reactions of ^235,238U,²³⁹Pu,and ²³²Th were calculated,and the average deviations of the independent yield charge and mass distributions from the evaluated data were less than 2%and 0.5%,respectively,and the average deviations of the cumulative yield charge and mass distributions from the evaluated data were less than 7%and 3%,respectively.2)The kinetic energy distribution of fission fragments,the variation of the average total kinetic energy of fragments with the incident neutron energy,and the correlation of mass-total kinetic energy of fragments were calculated for the neutron-induced ^235,238U,and ²³⁹Pu fission reactions.The comparison with the experimental data showed that the Modified Model was in good agreement with the experimental compared.3)The prompt fission neutron spectrum,the average energy of prompt fission neutrons,the average prompt fission neutron number and the incident neutron energy relationship were calculated,and the calculated results are in good agreement with the experimental data and evaluation data within a certain error range.4)Physical parameters such as prompt fission?spectrum and average energy of prompt fission?are calculated,and the calculation results are in good agreement with the experimental data and evaluation data within a certain error range.2.Design and optimization of TFGIC detector for the fission product measurementThrough the study principle of the TFGIC detector,the data processing iterative algorithm and procedure of fission product mass measurement based on the double kinetic energy theory were developed.The optimized design of TFGIC detector parameters was completed through simulation and modeling,and the structural design of the TFGIC detector was completed on this basis.The main design parameters of the TFGIC detector are determined as follows:1)the working medium is P-10 gas,and the flow gas mode is adopted.2)the outer diameter of the electrode is taken as 175 mm,the spacing between cathode and grid is taken as 31 mm,the spacing between grid and anode is taken as 5.5 mm,the voltage of the grid is grounded,and the ratio of the electric field strength between grid and anode to the electric field strength between cathode and grid,R,is greater than 1.42.3)the fission target PET is used as the substrate,the thickness is taken as 0.9?m,which is coated with 0.03?m thick gold film to ensure that the target has good conductivity,and the gold film is then coated with fissile material film,the thickness of which should be controlled at about 0.4?m.Based on the determination of TFGIC detector parameters and structure,the simulation study of the neutron-induced ²³⁸U fission process and the detector output signal was completed by using Geant4,Garfield++,COMSOL,ROOT,and other software tools,taking 2.5 Me V fast neutron vertical incidence in ²³⁸U fission target as an example,and the anode-grid correlation signal of TFGIC detector was obtained.The results of the two-dimensional amplitude spectrum of the correlation signal of the TFGIC detector were obtained,and the feasibility of the physical parameters of the TFGIC detector design was verified.3.Study on the correction method of TFGIC to measure the fission productA study on the correction methods of key measurement parameters of fission products based on the TFGIC detector,including the correction of Grid-inefficiency and the correction of energy loss of fission fragments in the fission target,was carried out.The main research results and conclusions are1)Grid-inefficiency correction method and Grid-inefficiency factor?studyBased on the Shockley-Ramo theory,the Grid-inefficiency correction is studied,and the correction equation related to the Grid-inefficiency factor?is established,based on which,a set of simulation calculation methods for the Grid-inefficiency factor?is developed for Parallel wire and Mesh types TFGIC.The comparison between the calculated results and experimental data shows that the method can describe the Grid-inefficiency factor values of different types of grids more accurately.To solve the problem that there is no empirical formula for calculating the mesh type?,an artificial neural network algorithm is used to develop an evaluation method for the prediction of mesh type?.The trained neural network can better reflect the mapping relationship between mesh-type parameters p,d,r,and?,which provides a new method for the correction of the Grid-inefficiency factor with the mesh-type TFGIC in the future.2)Study on the correction method of energy loss of fission fragments in fission targetBased on the Geant4 simulation of the energy loss law of typical fission fragments in fission target materials,a new fission fragment energy loss correction method,the energy loss compensation method,is proposed,and the principle and implementation steps of the method are elaborated.The feasibility of using the Geant4 model to describe the energy loss process of fission fragments in the fission target is effectively verified.The feasibility and applicability of the energy loss compensation method are methodologically verified by taking the experimental data of the 2 Me V neutron-induced ²³⁴U(n,f)fission reaction as an example,and the results show that the energy loss compensation method can better reflect the energy loss difference between light and heavy fission fragments in the fission target compared with the traditional extrapolation method,thus producing a better energy loss correction effect.4.Development and testing of fission measurement system for TFGIC detectorBased on the physical design and structural design of TFGIC,the TFGIC detector was processed and assembled,and a complete measurement device for the measurement of neutron-induced actinide fission product parameters was built,and then the following experimental tests were completed.1)The measurement of the Grid-inefficiency factor of the TFGIC detector was carried out,and the results showed that the Grid-inefficiency factors of the two sides of the TFGIC detector were?₁=0.061±0.016 and?₂=0.058±0.016,respectively,and the correction of the Grid-inefficiency of the output signal amplitude of each electrode of the detector was completed according to the measurement results of?.2)The energy resolution of the TFGIC detector and the energy scale of the system was tested using ²⁴¹Am,^238,239Pu and ^234,238U?-particle sources.The results show that the energy resolution of the detector is about 2.27%for ²⁴¹Am-?particles.3)Using ^234,238U fission target as?-particle sources,experimental tests on the energy-angle correlation information of charged particles with TFGIC detectors were carried out using the amplitude analysis method and the drift time method,respectively,and the amplitude analysis method was determined as the experimental data processing method for energy-angle correlation information acquisition.4)Based on the compact D-D neutron generator at Lanzhou University,the preliminary test of D-D neutron-induced U-target fission product measurement was carried out,which verified the feasibility of this measurement system for fission product measurement and laid the foundation for the next stage of more detailed experimental measurement of fission products.