Radiography principle relies on penetrating radiation (X, gamma, neutrons, …) generated by a source, more or less absorbed in the testpiece to be inspected.

Natural X-rays do not exist on earth. Their production is fully artificial.

In the field of non destructive testing they are generally obtained by the electron bombardment of a tungsten target .

A radiation detector (film, screen,…) converts the invisible radiating image into a visible image.

Extract from COFREND site