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利用不同材料的中子质量衰减系数不同而获取样品内部的结构潜像,属于吸收散射衬度成像;而相衬成像是基于中子的波动性,当中子波穿过样品时,由于样品对中子的折射,不同厚度、不同材质引入的相位差不同,从而导致波前畸变,畸变的波前在穿过样品后作为次波源互相干涉成像,从而获取样品内部结构潜像。研究工作通过数值模拟方法分析了中子相衬成像过程,并基于反应堆中子照相装置进行了不同条件下的多色热中子相衬成像实验。模拟与实验结果表明,在适当准直比条件下,铝材料边缘将出现明显的边缘增强效应,该效应与准直比、样品与转换屏之间的距离密切相关。
The use of different material neutron mass attenuation coefficient to obtain the internal structure of the sample latent image, which belongs to the absorption scattering contrast imaging, while phase contrast imaging is based on the neutron volatility, when the neutron wave through the sample, due to sample alignment The refraction, the different thickness and the different phase difference introduced by different materials lead to the wavefront distortion. The distorted wave front images interfere with each other as the secondary wave source after passing through the sample, so as to obtain the latent image of the internal structure of the sample. In this work, the imaging process of neutron phase contrast was analyzed by numerical simulation method and the multicolor thermal neutron phase contrast imaging experiment was carried out under different conditions based on reactor neutron radiography. Simulation and experimental results show that the edge of the aluminum material will have obvious edge enhancement effect at the proper collimation ratio, which is closely related to the collimation ratio and the distance between the sample and the conversion screen.