X-rays are produced by high voltage X-ray machines, whereas gamma rays are produced from radioactive isotopes such as Iridium 192. The X-ray or gamma rays are placed close to the material to be inspected and they pass through the material and are then captured on film. This film is then processed and the image is obtained as a series of grey shades between black and white.
The choice of which type of radiation is used, X-ray or gamma ray, depends on the thickness of the material to be tested. Gamma sources have the advantage of portability which makes them ideal for use e.g. in construction site working.
X-rays and gamma rays are very hazardous. Special precautions must be taken when performing radiography. Therefore the operator will use these with appropriate safety clothing or inside a protective enclosure and behind barriers and warning signals to ensure there are no hazards to himself or other personnel.