Gamma Radiation Definition

Gamma Rays or Gamma Radiation

A nucleus decaying by emission of a gamma ray
A nucleus decaying by emission of a gamma ray. Inductiveload/Wikimedia Commons/Public Domain

Gamma radiation or gamma rays are high-energy photons that are emitted by radioactive decay of atomic nuclei. Gamma radiation is very high-energy form of ionizing radiation, with the shortest wavelength.

Key Takeaways: Gamma Radiation

  • Gamma radiation (gamma rays) refers to the part of the electromagnetic spectrum with the most energy and shortest wavelength.
  • Astrophysicists define gamma radiation as any radiation with an energy above 100 keV. Physicists define gamma radiation as high-energy photons released by nuclear decay.
  • Using the broader definition of gamma radiation, gamma rays are released by sources including gamma decay, lightning, solar flares, matter-antimatter annihilation, the interaction between cosmic rays and matter, and many astronomical sources.
  • Gamma radiation was discovered by Paul Villard in 1900.
  • Gamma radiation is used to study the universe, treat gemstones, scan containers, sterilize foods and equipment, diagnose medical conditions, and treat some forms of cancer.


French chemist and physicist Paul Villard discovered gamma radiation in 1900. Villard was studying radiation emitted by the element radium. While Villard observed the radiation from radium was more energetic than the alpha rays described by Rutherford in 1899 or the beta radiation noted by Becquerel in 1896, he did not identify gamma radiation as a new form of radiation.

Expanding upon Villard's word, Ernest Rutherford named the energetic radiation "gamma rays" in 1903. The name reflects the level of penetration of radiation into matter, with alpha being least penetrating, beta being more penetrating, and gamma radiation passing through matter most readily.

Health Effects

Gamma radiation presents a significant health risk. The rays are a form of ionizing radiation, which means they have enough energy to remove electrons from atoms and molecules. However, they are less likely to ionization damage than less-penetrating alpha or beta radiation. The high energy of the radiation also means gamma rays possess high penetrating power. They pass through skin and damage internal organs and bone marrow.

Up to a certain point, the human body can repair genetic damage from exposure to gamma radiation. The repair mechanisms seems to be more efficient following a high-dose exposure than a low-dose exposure. Genetic damage from gamma radiation exposure may lead to cancer.

Natural Gamma Radiation Sources

There are numerous natural sources of gamma radiation. These include:

Gamma decay: This is the release of gamma radiation from natural radioisotopes. Usually, gamma decay follows alpha or beta decay where the daughter nucleus is excited and falls to a lower energy level with the emission of a gamma radiation photon. However, gamma decay also results from nuclear fusion, nuclear fission, and neutron capture.

Antimatter annihilation: The an electron and a positron annihilate each other, extremely high-energy gamma rays are released. Other subatomic sources of gamma radiation besides gamma decay and antimatter include bremsstrahlung, synchrotron radiation, neutral pion decay, and Compton scattering.

Lightning: The accelerated electrons of lightning produces what is called a terrestrial gamma-ray flash.

Solar flares: A solar flare may release radiation across the electromagnetic spectrum, including gamma radiation.

Cosmic rays: The interaction between cosmic rays and matter releases gamma rays from bremsstrahlung or pair-production.

Gamma rays bursts: Intense bursts of gamma radiation may be produced when neutron stars collide or when a neutron star interacts with a black hole.

Other astronomical sources: Astrophysics also study gamma radiation from pulsars, magnetars, quasars, and galaxies.

Gamma Rays Versus X-Rays

Both gamma rays and x-rays are forms of electromagnetic radiation. Their electromagnetic spectrum overlaps, so how can you tell them apart? Physicists differentiate the two types of radiation based on their source, where gamma rays originate in the nucleus from decay, while x-rays originate in the electron cloud around the nucleus. Astrophysicists distinguish between gamma rays and x-rays strictly by energy. Gamma radiation has a photon energy above 100 keV, while x-rays only have energy up to 100 keV.