A barn (symbol b) is a unit of area. Area is a Quantity expressing the two- Dimensional size of a defined part of a Surface, typically a region bounded by a closed Curve. While the barn is not an SI unit, it is accepted (although discouraged) for use with the SI. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process. Nuclear physics is the field of Physics that studies the building blocks and interactions of Atomic nuclei. In nuclear and Particle physics, the concept of a cross section is used to express the likelihood of interaction between particles Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them A barn is approximately equal to the cross sectional area of a uranium nucleus. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the
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Definition
1 barn (b) = 10−28 square metres (m²) = 100 square femtometres (fm²) = 10−24 square centimetres (cm²) (Most commonly used)
Commonly used prefixed versions
- 1 millibarn (mb) = 10−31 m².
- 1 microbarn (μb) = 10−34 m².
- 1 nanobarn (nb) = 10−37 m².
- 1 picobarn (pb) = 10−40 m².
- 1 femtobarn (fb) = 10−43 m².
Conversions
Calculated cross sections are often found in units of (GeV)−2(ℏc)2 = 0. The Planck constant (denoted h\ is a Physical constant used to describe the sizes of quanta. 3894 mb.
Origin
The etymology is clearly whimsical and jocular—the unit is said to be "as big as a barn" compared to the typical cross sections for nuclear reactions. A barn is an agricultural building used for storage and as a covered workplace In Nuclear physics, a nuclear reaction is the process in which two nuclei or nuclear particles collide to produce products different from the initial particles During wartime research on the atomic bomb, American physicists who were deflecting neutrons off uranium nuclei, (similar to Rutherford scattering) described the uranium nucleus as “big as a barn. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including In Physics, Rutherford scattering is a phenomenon that was explained by Ernest Rutherford in 1909 and led to the development of the orbital theory of the ” Physicists working on the project adopted the name barn for a unit equal to 10-24 square centimetres, about the size of a uranium nucleus. Initially they hoped the American slang name would obscure any reference to the study of nuclear structure; eventually, the word became a standard unit in particle physics. [1]
The origin of the barn is described in the February 2006 issue of symmetry magazine.
Shed
The shed was devised to described incredibly small areas. One shed is 10−48m2, or 10−24b. A shed is to the barn what a barn is to the square meter.
References
External links
- Official SI website: Table 8. Other non-SI units currently accepted for use with the International System Their use is not encouraged.
- IUPAC citation for this usage of "barn"
- Article on cross-section
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