Barn (unit)
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A barn is a unit of area, abbreviated mostly as "bn", equal to 10−28 m2. Although not an official SI unit, it is widely used by nuclear physicists, since it is convenient for expressing the cross sectional area of nuclei and nuclear reactions. A barn is approximately equal to the area of a uranium nucleus.
The etymology is clearly whimsical—the unit is said to be "as big as a barn" compared to the typical cross sections for nuclear reactions. However this proved useful at the time this term was coined—by weapons researchers during World War 2—since it served to obscure the subject under discussion.
External links
- IUPAC citation for this usage of "barn" (http://www.iupac.org/goldbook/B00598.pdf)
- Article on cross-section (http://www-ed.fnal.gov/painless/htmls/cross.html) at Painless Physicsde:Barn fr:Barn