Radiographic testing is one of the most widely used methods in industry because it is highly sensitive and provides a permanent record of the inspection results.

X-rays are widely used in non-destructive testing because they make it possible to examine internal structures, changes in thickness and structure, and assembly details without damaging the material.

In this method, the test object is exposed to a beam of radiation (X-rays or gamma rays) from a source. As the radiation passes through the material, part of it is absorbed depending on the properties of the material; it then reaches the film placed behind the object and exposes it. Because discontinuities attenuate the radiation differently, the intensity of the radiation passing through them, and therefore the film density it produces, will also differ. After the film is processed, these density differences reveal the discontinuities.

Various radiation sources can be used for radiographic testing: X-ray tubes or gamma-emitting isotopes. The X-ray energy range used in industrial radiography is generally 50 kV to 350 kV, depending on the type and thickness of the material. The best-known and most widely used gamma sources are Ir-192 and Co-60; isotopes such as Se-75, Yb-169 and Tm-170 are also used in industrial radiography.

Electrically generated X-rays and gamma rays emitted by radioactive isotopes are absorbed by the material they pass through, and absorption increases with thickness, so denser materials absorb more radiation. X-rays and gamma rays are both electromagnetic waves and differ only in wavelength. Their wavelengths are so short that they are invisible and can penetrate materials. Like light, they affect the silver bromide crystals in the film and form an image in proportion to the radiation intensity reaching it.