gamma (g ) rays Gamma rays are electromagnetic waves with very short wavelength (< 0.1nm). Using the expression E = hn = hc/l , we can calculate the energy associated with a gamma photon. This comes out to be > 10 keV. Gamma rays behave more like particles than waves, due to their short wavelength. A gamma ray photon when passing through matter scatters a free electron on its way. In this process it loses kinetic energy and its own wavelength increases. This type of scattering is called Compton scattering*. When a gamma ray encounters a bound electron, it knocks off the electron from its orbit. There is a third possibility; the gamma ray photon materializes into electron positron pair. This takes place in the presence of electric field of the nucleus. This is known as pair production. All these processes produce ionization in the medium.

Gamma rays are produced by nuclear transformations. Various nuclear species exhibit different excited states. An excited nucleus de excites and releases a gamma ray photon. Decay of radioactive nuclei also often produces gamma rays. One such source is ₂₇Co⁶⁰.