Techniques Of Scattering Correction For Quantitative Neutron Digital Imaging

Neutron radiography is an early developed and mature NDT/NDE technique. In recent years, digitalized neutron radiography, that is: neutron digital imaging, appears, the theory, technique and application of which have been further investigated and developed. Quantitative neutron digital imaging, as a derivation of neutron digital imaging, can extract the quantitative information of a certain component in the sample from gray level signals of low light level imaged neutron images; therefore, it is favored by technicians in NDT/NDE.A mass point imaged by neutron digital imaging system can be represented in terms of PSF. Working on the CCD-based neutron low light level digital imaging system, aiming at the adverse situation that scattering neutron can directly affect the quantitative evaluation in NDT, the imaging degradation principle caused by scattering neutron is studied and analyzed. The process that scattering neutron induces imaging degradation is characterized by PSF superposition; by means of Monte Carlo method, the scattering PSF of H2O is simulated and modeled as analytical functions with sample thickness and sample-to-detector distance as their parameters, the calculation of which is also presented. Furthermore, the effectiveness the PSF model is verified by numerical simulation of neutron imaging. Results show that the numerically simulated neutron image is approximated by convoluted image using analytical PSF function. For one certain sample, the scattering PSF under different condition can be calculated directly, immediately and accurately using analytical scattering PSF without repetitive modeling. After modeling scattering PSF of neutron imaging, on the basis of the ideal of Van Cittert iteration, a space-domain iterative algorithm is presented to perform scattering correction on neutron images. Experimental study shows that after scattering correction, the scattering component affecting neutron image of H2O samples featured with various geometries and different sample-to-detector distances is well inhibited, and the thickness of these samples calculated from restored images approach their real thickness, which shows that the proposed neutron scattering correction algorithm is feasible and effective.The result of this thesis indicated that constructing analytical scattering PSF using Monte Carlo method to perform scattering correction on neutron images is an effective method to reduce the influence of scattering neutrons on imaging quality, by which neutron digital imaging system is applied to quantitative neutron digital imaging. Thus, it proves this study to be with theoretical guidance significance.