5-1. General. X-ray and gamma ray radiographic inspection utilizes the penetrating power of radiation to reveal the
interior of objects as recorded on film. The extent of recorded information is dependent upon three prime factors which
are responsible for an object to absorb radiation to varying degrees. These are:
The composition of the object.
The product of the density and the thickness of the object.
The energy of the X-ray gamma rays which are incident upon the object. Its discontinuities cause an
apparent change in these characteristics and thus make themselves detectable
Exposure to excessive radiation is harmful to human beings. While most X-ray equipment is
designed to minimize the danger of exposure to direct or stray radiation, certain precautions
must be observed. Radiation safety precautions are discussed In paragraph 5-11.
X-rays and gamma rays are forms of electromagnetic radiation, as are visible light, ultraviolet light, infrared waves, radio
waves, and cosmic rays. The distinguishing characteristics of X-rays is their short wavelength. The penetrating power of
X-rays is dependent upon the wavelength In an inverse relationship; that is, the shorter the wavelength, the higher the
energy, and vice versa. Differences in properties and effects between X-rays and gamma rays are largely a matter of
degree. The major advantage of using gamma rays is the fact that gamma ray sources are small and provide access to
small spaces, thereby simplifying exposure technique.
5-2. Purpose. Radiography is a useful non-destructive inspection method designed to detect internal discontinuities is
many parts and substances.
5-3. Advantages. Radiography may be applied to the inspection of castings, welds, and assembled components.
Various metals, both ferrous and nonferrous, as well as nonmetallics such as ceramics and plastics, can successfully be
5-4. Disadvantages. Radiography is not a cure-all and should be used only when conditions are satisfied Multiple film
techniques and other special methods make radiography a versatile tool for evaluation.
Although radiography will reveal the interior of opaque objects, it cannot detect all types or
irregularities or discontinuities. Small defects In thick objects such as fine cracks or laminations
are difficult to detect. In applying radiography as an Inspection method, the sensitivity of the
method must be kept in mind.
5-5. Applications. There are some basic guidelines that may be used to determine situations to which radiography is
applicable. Some of the basic requirements that must be satisfied so that radiography may be successfully applied are:
The defect which is of interest must cause a detectable change in apparent thickness, density, or
The part should be reasonably homogeneous, so that an indication of a defect may be observed.
The configuration of the part to be tested, or the area when surrounds it, must be such that access to both
sides is provided.
The defect to be detected must be properly oriented in the path of the radiation beam.
5-6. Inspection Techniques. The following paragraphs describe various Inspection techniques used in radiography.
General. The following paragraphs describe the factors that determine whether or not a particular radiographic
inspection is sufficiently sensitive to detect small defects. Sensitive radiography requires maximum