Properties of gamma rays pdf is the latest accepted revision, reviewed on 5 December 2017. This article is about the term’s use in physics.
Gamma rays are emitted during nuclear fission in nuclear explosions. Gamma radiation detected in an isopropanol cloud chamber. It consists of photons in the highest observed range of photon energy.
Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays. Rutherford had previously discovered two other types of radioactive decay, which he named alpha rays and beta rays.
The decay of an atomic nucleus from a high energy state to a lower energy state, a process called gamma decay, produces gamma radiation. Natural sources of gamma rays on Earth are observed in the gamma decay of radionuclides and secondary radiation from atmospheric interactions with cosmic ray particles.
There are rare terrestrial natural sources, such as lightning strikes and terrestrial gamma-ray flashes, that produce gamma rays not of a nuclear origin. Additionally, gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced, that in turn cause secondary gamma rays via bremsstrahlung, inverse Compton scattering, and synchrotron radiation. However, a large fraction of such astronomical gamma rays are screened by Earth’s atmosphere and can only be detected by spacecraft.
However, this is not a strict definition, but rather only a rule-of-thumb description for natural processes. Electromagnetic radiation from radioactive decay of atomic nuclei is referred to as “gamma rays” no matter its energy, so that there is no lower limit to gamma energy derived from radioactive decay. This radiation commonly has energy of a few hundred keV, and almost always less than 10 MeV. In astronomy, gamma rays are defined by their energy, and no production process needs to be specified.
The energies of gamma rays from astronomical sources range to over 10 TeV, an energy far too large to result from radioactive decay. A notable example is the extremely powerful bursts of high-energy radiation referred to as long duration gamma-ray bursts, of energies higher than can be produced by radioactive decay. These bursts of gamma rays are thought to be due to the collapse of stars called hypernovae. This historically allowed a clear distinction between X-rays and gamma rays.
Today, the research literature often describes photons depending on their source. For example, one group of scientists might describe a 1 MeV photon as a gamma ray, while another group use the term X-ray.
The first gamma ray source to be discovered historically was the radioactive decay process called gamma decay. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium. Villard knew that his described radiation was more powerful than previously described types of rays from radium, which included beta rays, first noted as “radioactivity” by Henri Becquerel in 1896, and alpha rays, discovered as a less penetrating form of radiation by Rutherford, in 1899.