Radiographic examination involves using the property of rectilinear propagation of electro magnetic waves such as both X - rays and Gamma Rays. In aeronautic industry only X - ray examination find good application. The quality or penetrating power of X - rays increases with kilovoltage applied across the filament and target and this depends purely on the density and thickness of the material to be penetrated.

Principle of (X - ray) Radiographic Examination :

The intensity of a beam of X - rays or rays undergoes local attenuation as it passed through a heterogeneous body, due to the absorption and scattering of radiation by the object concerned.
As a result the beam emerging from the object forms at the surface of the film areas of differing intensity which together make up the radiation image.

The image obtained when the film is developed is a negative reproduction of the radiation image. The film produces a two dimensional shadow graphic projection of three dimensional part under examination.

Interpretation of X - ray film is only distinguishing between areas of different density or film blackness. 
Black areas represent less absorption of X - rays due to presence of defects compared to adjacent homogeneous areas of less black areas. 

Whereas light areas in a homogeneously back area show some foreign metals of high absorption. 
The shadow graph is purely due to selective absorption of X - rays by matters in its path.

Radiographic examination finds many application in inspecting casting, welding, structures etc. for internal soundness, process control checks, development of new casting and process technology, in evaluation of internal assemblies like electronic circuitry, injection nozzle continuity of filament inside assay.

X - rays inspection plays vital role in inspecting areas without disassembly which otherwise warrants disassembly involving labour and time.