| Neutron radiography is an excellent non-destructive testing technology.It complements traditional X-ray and gamma-ray radiography and plays an irreplaceable role in non-destructive testing.According to neutron energy,neutron radiography can be divided into cold neutron radiography,thermal neutron radiography,epithermal neutron radiography and fast neutron radiography(FNR).FNR is more suitable for the detection of large size and low Z material in the inner structure of large-scale metal shell because of its strong penetration ability.FNR is an important detection method for radioactive substances,and it has widely application prospects in aerospace,national defense,military industry,safety,nuclear energy and other fields.The advantages of accelerator neutron source are small target(near point source),less scattering and miniaturization.It can provide high quality neutron beam for FNR.High-quality image acquisition requires high neutron fluence,high neutron energy and better monochromaticity.The High Intensity D-T Fusion Neutron Generator(HINEG)was designed and constructed by the Institute of Nuclear Safety Technology of the Chinese Academy of Sciences.It can produce 14 MeV D-T neutron of 6.4×1012 n/s,which is an ideal neutron source for FNR.The key technologies of collimating and imaging of the fast neutron radiography system based on HINEG were studied in this work..The main research contents include:(1)The key factors of FNR based on D-T neutron source was studied.Due to the problem of scattering neutron interference intensity and high background of gamma ray in imaging field,Monte Carlo method was used to study the influence of collimator shield structure on the characteristic parameters.The scattering neutrons and gamma rays were reduced through optimizing the structure,and high quality neutron beams were obtained.Monte Carlo method was used to study the effects of material,mass ratio and thickness of neutron conversion screen on proton yield and angular distribution,fluorescence photon intensity.In addition,according to the output fluorescence characteristics of the neutron conversion screen,testing materials,size and testing requirements,the parameters and type selection of film and CCD cameras were studied respectively.(2)The performance of the FNR system based on HINEG was simulated and analyzed.Due to the problem that the spatial resolution of the FNR system is difficult to improve,the effects of collimation ratio,sample thickness and distance from sample to image detector on scattered neutrons,the spatial resolution and image contrast of the FNR system were studied by Monte Carlo method.The optimal layout scheme and imaging parameters of the FNR system were obtained.The results show that the spatial resolution of the FNR system based on film is～0.37 mm and that based on CCD camera is～0.85 mm.(3)The experimental verification of the FNR system based on HINEG was carried out.A FNR system based on HINEG and the optimal layout of the FNR system was constructed.The experimental scheme was designed according to the performance simulation of the FNR system.The spatial resolution of the FNR system based on film and digital CCD camera was verified.The results show that the spatial resolution of film imaging is～0.5 mm,and that of CCD camera imaging is～1.0 mm,the relative deviations from the theoretical results are 32.4%and 17.6%,respectively.In summary,the key technologies of collimating and imaging of the fast neutron radiography system based on HINEG were studied in this paper.The collimator shield was optimized to reduce the scattering neutron and gamma ray of neutron beam effectively and thus improving the quality of neutron beam;and the optimal layout scheme was obtained by optimizing the layout of the FNR system.A FNR system based on HINEG was constructed and obtained the better spatial resolution of～0.5 mm.The research results of this paper can provide theoretical and technical guidance for FNR and promote the development of FNR technology. |
PDF Full Text Request