Gamma Radiation Definition

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.

History

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.

Natural Gamma Radiation Sources

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Nuclear Radiation Definition

By Anne Marie Helmenstine, Ph.D.

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.

Sources

• L'Annunziata, Michael F. (2007). Radioactivity: introduction and history. Elsevier BV. Amsterdam, Netherlands. ISBN 978-0-444-52715-8.
• Rothkamm, K.; Löbrich, M. (2003). "Evidence for a lack of DNA double-strand break repair in human cells exposed to very low x-ray doses". Proceedings of the National Academy of Sciences of the United States of America. 100 (9): 5057–62. doi:10.1073/pnas.0830918100
• Rutherford, E. (1903). "The magnetic and electric deviation of the easily absorbed rays from radium." Philosophical Magazine, Series 6, vol. 5, no. 26, pages 177–187.
• Villard, P. (1900). "Sur la réflexion et la réfraction des rayons cathodiques et des rayons déviables du radium." Comptes rendus, vol. 130, pages 1010–1012.