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A gamma ray , or gamma radiation (symbol γ or γ {\displaystyle \gamma } ), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves and so imparts the highest 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 based on their relatively strong penetration of matter; in 1900 he had already named two less penetrating types of decay radiation (discovered by Henri Becquerel) alpha rays and beta rays in ascending order of penetrating power. Gamma rays from radioactive decay are in the energy range from a few kiloelectronvolts (keV) to approximately 8 megaelectronvolts (~8 MeV), corresponding to the typical energy levels in nuclei with reasonably long lifetimes. The energy spectrum of gamma rays can be used to identify the decayi...

The first gamma ray source to be discovered was the radioactive decay process called gamma decay . In this type of decay, an excited nucleus emits a gamma ray almost immediately upon formation.note 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. However, Villard did not consider naming them as a different fundamental type. Later, in 1903, Villard's radiation was recognized as being of a type fundamentally different from previously named rays by Ernest Rutherford, who named Villard's rays "gamma rays" by analogy with the beta and alpha rays that Rutherford had differentiated in 1899. The "ra...

Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes such as potassium-40, and also as a secondary radiation from various atmospheric interactions with cosmic ray particles. Some rare terrestrial natural sources that produce gamma rays that are not of a nuclear origin, are lightning strikes and terrestrial gamma-ray flashes, which produce high energy emissions from natural high-energy voltages. Gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung , inverse Compton scattering and synchrotron radiation. A large fraction of such astronomical gamma rays are screened by Earth's atmosphere. Notable artificial sources of gamma rays include fission, such as occurs in nuclear reactors, as well as high energy physics experiments, such as neutral pion decay and nuclear fusion. A sample of gamma ray-emitting mate...

Penetration of matter edit Due to their penetrating nature, gamma rays require large amounts of shielding mass to reduce them to levels which are not harmful to living cells, in contrast to alpha particles, which can be stopped by paper or skin, and beta particles, which can be shielded by thin aluminium. Gamma rays are best absorbed by materials with high atomic numbers ( Z ) and high density, which contribute to the total stopping power. Because of this, a lead (high Z ) shield is 20–30% better as a gamma shield than an equal mass of another low- Z shielding material, such as aluminium, concrete, water, or soil; lead's major advantage is not in lower weight, but rather its compactness due to its higher density. Protective clothing, goggles and respirators can protect from internal contact with or ingestion of alpha or beta emitting particles, but provide no protection from gamma radiation from external sources. The higher the energy of the gamma rays, the thicker the shielding m...

Gamma rays provide information about some of the most energetic phenomena in the universe; however, they are largely absorbed by the Earth's atmosphere. Instruments aboard high-altitude balloons and satellites missions, such as the Fermi Gamma-ray Space Telescope, provide our only view of the universe in gamma rays. Gamma-induced molecular changes can also be used to alter the properties of semi-precious stones, and is often used to change white topaz into blue topaz. Non-contact industrial sensors commonly use sources of gamma radiation in refining, mining, chemicals, food, soaps and detergents, and pulp and paper industries, for the measurement of levels, density, and thicknesses. Gamma-ray sensors are also used for measuring the fluid levels in water and oil industries. Typically, these use Co-60 or Cs-137 isotopes as the radiation source. In the US, gamma ray detectors are beginning to be used as part of the Container Security Initiative (CSI). These machines are advertised to ...

Gamma rays cause damage at a cellular level and are penetrating, causing diffuse damage throughout the body. However, they are less ionising than alpha or beta particles, which are less penetrating. Low levels of gamma rays cause a stochastic health risk, which for radiation dose assessment is defined as the probability of cancer induction and genetic damage. High doses produce deterministic effects, which is the severity of acute tissue damage that is certain to happen. These effects are compared to the physical quantity absorbed dose measured by the unit gray (Gy). Body response edit When gamma radiation breaks DNA molecules, a cell may be able to repair the damaged genetic material, within limits. However, a study of Rothkamm and Lobrich has shown that this repair process works well after high-dose exposure but is much slower in the case of a low-dose exposure. Risk assessment edit The natural outdoor exposure in the United Kingdom ranges from 0.1 to 0.5 µSv/h with significant inc...

The following table shows radiation quantities in SI and non-SI units: Ionizing radiation related quantities view  ‧  talk  ‧   edit Quantity Unit Symbol Derivation Year SI equivalence Activity ( A ) becquerel Bq s−1 1974 SI unit curie Ci 3.7 × 1010 s−1 1953 3.7 × 1010 Bq rutherford Rd 106 s−1 1946 1,000,000 Bq Exposure ( X ) coulomb per kilogram C/kg C⋅kg−1 of air 1974 SI unit röntgen R esu / 0.001293 g of air 1928 2.58 × 10−4 C/kg Absorbed dose ( D ) gray Gy J⋅kg−1 1974 SI unit erg per gram erg/g erg⋅g−1 1950 1.0 × 10−4 Gy rad rad 100 erg⋅g−1 1953 0.010 Gy Equivalent dose ( H ) sievert Sv J⋅kg−1 × W R 1977 SI unit röntgen equivalent man rem 100 erg⋅g−1 x W R 1971 0.010 Sv Effective dose ( E ) sievert Sv J⋅kg−1 × W R x W T 1977 SI unit röntgen equivalent man rem 100 erg⋅g−1 x W R x W T 1971 0.010 Sv The measure of the ionizing effect of gamma and X-rays in dry air is called the exposure, for w...

Nuclear physics Nucleus  · Nucleons (p, n)  · Nuclear matter  · Nuclear force  · Nuclear structure  · Nuclear reaction Models of the nucleus Liquid drop  · Nuclear shell model  · Interacting boson model  · Ab initio Nuclides' classification Isotopes – equal Z Isobars – equal A Isotones – equal N Isodiaphers – equal N  −  Z      Isomers – equal all the above Mirror nuclei – Z ↔ N Stable  · Magic  · Even/odd  · Halo (Borromean) Nuclear stability Binding energy  · p–n ratio  · Drip line  · Island of stability  · Valley of stability  · Stable nuclide Radioactive decay Alpha α  · Beta β (2β, β+)  · K/L capture  · Isomeric (Gamma γ  · Internal conversion)  · Spontaneous fission  · Cluster decay  · Neutron emission  · Proton emission Decay energy  · Decay chain  · Decay product  · Radiogenic nuclide Nuclear fission Spontaneous  · Products (pair breaking)  · Photofission Capturing processes electron (2×)  · neutron (s  · r)  · proton (p  · rp...