Research On Inversion Algorithm Of Neutron Energy Spectrum And Measurement Of Neutron Characteristics Of Compact D-D Neutron Generator

With the development of nuclear science and technology,the research and application of neutron physics and neutron application technology are becoming more and more extensive.Accelerator neutron sources based on ²H（d,n）³He（D-D）and³H（d,n）⁴He（D-T）reactions have important application value in the field of basic neutron physics and neutron application technology because of their characteristics of producing high yield quasi monenergy fast neutrons under the condition of low energy D-beam.In recent years,Lanzhou University has successfully developed the compact D-D neutron generator,which has the advantages of high neutron yield,good monochromator,miniaturization and controllability,and has important application value in the technical fields of neutron imaging and neutron activation analysis.The compact D-D neutron generator uses D（d,n）³He deuterium beam bombardment to self-inject deuterium target operation mode,and generates D（d,n）3He reaction to produce non-pulsed fast neutrons.In order to accurately evaluate the neutron property distribution of the compact D-D neutron generator,this paper carries out research on neutron spectrum inversion algorithm based on nuclear recoil method.Through comparative analysis and optimization of neutron spectrum inversion algorithm,further carries out experimental measurement of the neutron property of the compact D-D neutron generator,and evaluates the neutron radiation field distribution of the compact D-D neutron generator.In this work,hydrogen-rich scintillation detector is selected to carry out neutron energy spectrum inversion algorithm based on nuclear recoil method.According to the neutron energy spectrum inversion theory of nuclear recoil method.The Direct solution（least square method,LU decomposition method,QR decomposition method）,iterative algorithms（GRAVEL iteration algorithm,MLEM iteration algorithm,GOLD and Boosted-GOLD iteration algorithm,Direct-D iteration algorithm,Probability iteration algorithm,R-L and its derivative algorithm）and artificial intelligence algorithm are established method（particle swarm optimization algorithm,BP neural network algorithm）and other 11 neutron spectral decomposition algorithms.By simulating the inversion of 2.5 Me V D-D quasi-simple energy neutron spectrum,D-D neutron spectrum with Gaussian distribution,²⁵²Cf fission neutron spectrum and Am-Be neutron spectrum,the scientific nature and reliability of the inversion algorithm are verified.The neutron energy spectrum solution algorithm based on iterative algorithm is recommended as the main method.In view of the problem of how to achieve convergence of the iterative algorithm,the mean square error（MSE）and the iterative index function J^（k）are proposed in this work as the judgment conditions of the optimal number of iterations,and the relationship between the MSE value and the iterative index function J^（k）in different algorithms of the above four neutron spectra with the number of iterations is simulated to obtain the optimal number of iterations and the minimum MSE value.The convergence condition of the iterative algorithm is determined.In this work,a fast neutron energy spectrum measuring spectrometer was built based on EJ309 liquid scintillation detector and SY plastic scintillation detector,and the neutron and gamma signals were screened by PSD method（n-γdiscrimination）.Based on the above six iterative algorithms（GRAVEL iteration,MLEM iteration,GOLD and Boosted-GOLD iteration,Direct-D iteration,Probability iteration,R-L and its derivations）,typical D-D quasi-single energy neutron spectrum measurement is completed in this work.Compared with other iterative algorithms,the 90°neutron spectrum obtained by GRAVEL iterative algorithm is in good agreement with the D-D quasi-single energy neutron spectrum calculated by theoretical evaluation.After discussion and analysis,iterative GRAVEL algorithm is recommended as the optimal method for the subsequent experimental measurement of the neutron characteristics of compact D-D neutron generators.Based on the developed iterative neutron spectrum inversion algorithm,EJ309liquid flash detector and SY plastic flash detector were used to measure the neutron spectrum and flux Angle distribution in compact D-D neutron generator.The neutron energy spectrum and flux Angle distributions at nine neutron exit angles of 30°,45°,60°,75°,90°,105°,120°,135°and 150°are given.In addition,the neutron radiation field distribution of the compact D-D neutron generator is obtained by inputting the neutron source characteristics parameters calculated by the TARGET program into the MCNP program.By comparing the experimental measurement results with the theoretical simulation results,the neutron radiation field distribution of the compact D-D neutron generator is given in this evaluation,which provides reliable source data and technical support for the application of the compact D-D neutron generator in the field of neutron physics and neutron application technology.