X-rays : are produced whenever high energy electrons suddenly give up energy. This can be done either by accelerating electrons to a high speed and then stopping them suddenly, or by these high speed electrons striking others and knocking them out of their normal positions. When these dislodged electrons fall back into place, they give of x-rays. The position of X-rays in the electromagnetic spectrum.

Radiography: essentially employs the transmission mode in which the shadow image is recorded on an integrated type of detector such as X-ray film. In radiography method, different types of radiation sources and detectors are used. Generally, the technique is named after the source and detector combination employed. These methods produce an image display that often tends itself for interpretation.
Radiography is based on differential absorption of penetrating radiation (either electromagnetic radiation of very short-wave length or particulate radiation) by the part or test object being tested. Because of differences in density and variations in thickness of the part, or differences in absorption characteristics caused by variation in composition, different portion of a test piece absorb different amount of penetrating radiation. Unabsorbed radiation passing through the part can be recorded on film or photosensitive paper, viewed on fluorescent paper, or monitored by various types of radiation detectors
Radiography utilizes penetrating electromagnetic radiation in the form of X-rays or gamma rays. In case of particulate radiation, neutron radiography is an example, which refers to radiographic inspection using a stream of neutrons rather than electromagnetic radiation.

X-ray and Gamma radiography
Conventional radiography refers to radiography with X and Gamma rays. It is most widely practiced by industry for quality control of welds, casting and assemblies. The radiograph of a specimen produced on a photographic film would show its internal conditions as interpreted from the density (blackening) variation on the film.
Industrial X-ray machines in the range of 50-400 KeV are used for inspection of metal thickness up to 7.5 cm steel equivalents. For higher thickness, BETATRONS and LINEAR ACCELERATORS up to 30 MeV are used.
Artificially produced gamma radiography sources such as lridiium-192 and Cobalt-60 provide some distinct advantages over X-ray machines. The gamma radiography equipments are compact, rugged, ideal for fieldwork and much cheaper, when compared to the X-ray machines of equivalent energy. Iridium-192 and Cobalt-60 combined together can cover inspection range of 10-200 mm of steel equivalents.