Barn (unit)

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.

External links

• IUPAC citation for this usage of "barn"
• http://www-ed.fnal.gov/painless/htmls/cross.html