Gamma rays are used in many different ways; one of the most common uses is inspecting castings and welds for defects that are not visible to the naked eye. Another common use of gamma rays is in the treatment of certain types of cancer.
Gamma rays are a form of electromagnetic radiation, and they have the greatest energy of all forms of electromagnetic radiation. Gamma rays can easily penetrate most materials, including lead. Gamma rays are classified as ionizing radiation and are therefore hazardous to living cells. When gamma rays pass through matter, they strike against atoms, causing those atoms to eject electrons. This process of ionization is what causes harm to living cells.
Gamma rays can be produced naturally or as the result of a nuclear reaction as fission. During fission, gamma rays are produced as the result of splitting the nucleus of an atom. Naturally produced gamma rays come from the radioactive decay of certain atoms, such as Potassium 40.
Gamma rays can be detected with photographic film or plates. When used to inspect defects, gamma rays are passed through an object onto photographic film. The image on the film can reveal defects that are otherwise not visible.