Investigation On Scatter Problem In Twin-axis Radiographic System

High Energy Flash X-ray Radiography (HEFXR) is an effectual and critical diagnostic technique to determine the geometrical and physical characteristics of the mock nuclear weapon primary implosion. Scattering of photons is an important physical process which can cause significant image degradation and disturb the extraction of information about interface locations and density distributions in the HEFXR system. Forward scatter, which is the main one of factors affecting image in single-axis radiography, has been studied thoroughly. An advanced precision of information can be obtained in multi-axis radiography, however a new problem of axis-to-axis interfere which is part of scatter of multi-axis radiography is brought in. In order to understand scatter of twin-axis radiography, some problems on side scatter are investigated, including the factors affecting sides scatter, the impact of side scatter on density measurement, the main source of side scatter and the methods of reducing side scatter.The factors affecting side scatter are analyzed in simple geometry including the distance between detecting plane and the center of the object, optical path, the parameters of front-protected-cell (FPC), the parameters of X-ray source and the thickness of back-protected-cell (BPC). The follow conclusions are obtained. The exposure and distribution of side scatter are different with varied positions of detecting plane. And the increment of the distance between the detector and FTO may not lead to the reduction of side scattered exposure. The direct exposure received by off-axis detector is so much that the signal can be submersed. The expression for calculating the height of the main collimator is given in order to resolve this problem. When the size of the object is fixed, the distribution of side scatter is deemed to be invariable with the same weight of the object. FPC makes great contribution to side scatter. The way of increasing the distance between FPC and FTO can be used to decrease side scatter partly. The side scatter is decreased with the emanative angle of the electron beam striking target enhanced. The side scatter depends on BPC to the least extent.A gross estimate of scatter levels is made in the integrated twin axis radiography, and some measures are taken pertinently. The results are as follows. Without back cone side scatter and forward scatter have the same amount level, with back cone side scatter is far less than forward scatter for routine radiographic system. The thicker collimator can result in the hardly changing ratio of direct to forward scatter, yet the larger ratio of direct to side scatter. The back cone at the same axis is the main source of side scatter. In order to reduce side scatter the methods provided by this paper are taken to decrease the side-scattered exposure by one amount level.In summary, the investigated results of this dissertation would redound to understand scatter of twin-axis radiography in particular axis-to-axis interfere and some results can be used for designing the layout of the multi-axis radiographic system.