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Gamma ray

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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...
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Properties

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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...
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Units of measurement and exposure

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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...
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