T.O. 33B-1-16-3o. They do not affect fuel cells or munitions.All of these properties contribute in some degree to the understanding of the radiographic process. Most important ofthese in terms of usefulness to NDI are the differential absorption of radiation in matter and the ability of radiation toexpose film. In the remainder of this chapter the term “X-rays” will be more prevalent since that form of radiation ismost used. Except where noted the discussion will also apply to gamma rays.6.1.2.1 DifferentialAbsorptioninMatter.A material discontinuity, such as a void or change in configuration, (see Figure 6-2) changes the effective thickness of amaterial, and thus changes the degree of radiation absorption. Since all radiation that is not absorbed or scatteredwithin a material is transmitted, the amount of transmitted radiation varies with localized changes in effective materialthickness.Figure 6-2. Diagram of Radiographic Exposure.6.1.2.1.1It is the transmitted radiation intensity that is generally used to find a material defect. If the material discontinuityrepresented in Figure 6-3 were a foreign material inclusion, it also would cause a change in the apparent compositionof the material and again result in a change in the transmitted radiation intensity. The degree of this change would bedependent on the relative effects of the base material and the included material on the incident radiation.
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