It is emitted in one of the three types of natural Radio activity. It is the most energetic form of Electromagnetic Radiation, with a very short wavelength of less than 10-10 meters.

Gamma rays are essentially very energetic X-Rays emitted by excited nuclei. They often accompany alpha or beta particles, because a nucleus emitting those particles may be left in an excited (higher-energy) state.

Gamma-ray sources are used in medicine for cancer treatment and for diagnostic purposes, and in industry for the inspection of castings and welds.