Radiation of gamma rays which consist of very high-frequency electromagnetic radiation, similar in nature to X-rays but of shorter wavelength emitted by the nuclei of radioactive substances during decay or by the interactions of high-energy electrons with matter.

Gamma emission usually occurs as part of alpha or beta emissions; however, they are less ionizing in their effect than alpha and beta particles, but are dangerous nevertheless because they can penetrate deeply into body tissues; such as, bone marrow.

Controlled application of gamma radiation is important in the diagnosis and treatment of various conditions, including skin cancer and malignancies deep within the body.

Gamma radiation is also used to kill bacteria and other micro-organisms, to sterilize medical devices, and to change the molecular structure of plastics to modify their properties.