T.O. 33B-1-1
6-3
o. 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 of
these in terms of usefulness to NDI are the differential absorption of radiation in matter and the ability of radiation to
expose film. In the remainder of this chapter the term “X-rays” will be more prevalent since that form of radiation is
most used. Except where noted the discussion will also apply to gamma rays.
6.1.2.1
Differential Absorption in Matter.
A material discontinuity, such as a void or change in configuration, (see Figure 6-2) changes the effective thickness of a
material, and thus changes the degree of radiation absorption. Since all radiation that is not absorbed or scattered
within a material is transmitted, the amount of transmitted radiation varies with localized changes in effective material
thickness.
Figure 6-2. Diagram of Radiographic Exposure.
6.1.2.1.1
It is the transmitted radiation intensity that is generally used to find a material defect. If the material discontinuity
represented in Figure 6-3 were a foreign material inclusion, it also would cause a change in the apparent composition
of the material and again result in a change in the transmitted radiation intensity. The degree of this change would be
dependent on the relative effects of the base material and the included material on the incident radiation.
