There are two types of electromagnetic radiation: X rays and γ-rays. X-rays are photons emitted from the nucleus-surrounding atomic shells, which is the space where the electrons move or during velocity fluctuations of any charge-carrying particle, mainly electrons. γ-rays result due to instability of the atomic nucleus and from particle annihilation.
γ-Ray photon's possible energy values span a range of 0.01 to 17.6 MeV. They are normally emitted due to instability of an atomic nucleus during it's subsequent spontaneous transformation. In addition to transformation, γ-ray bursts also occur due to the decay of subatomic particles (e.g electron-positron pair annihlation) and electomagnetic fluctuations (velocity fluctuations of high-energy electrons in cosmic magnetic fields).
- ↑ IARC Working Group on the Evaluation of Carcinogenic Risk to Humans. Radiation. Lyon (FR): International Agency for Research on Cancer; 2012. (IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 100D.) X- AND γ-RADIATION.