- Plural of barn
A barn (symbol b) is a unit of area
. While the barn is not an
unit, it is
accepted (although discouraged) for use with the SI. Originally
used in nuclear
for expressing the cross
area of nuclei and nuclear reactions, today it is
used in all fields of high energy
to express the cross sections of any scattering
process. A barn is approximately equal to the cross sectional area
of a uranium
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.
Calculated cross sections are often found in
units of (GeV
= 0.3894 mb.
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
s. During wartime
research on the atomic bomb, American physicists who were
deflecting neutrons off uranium nuclei, (similar to Rutherford
) described the uranium nucleus as “big as a barn.”
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.
The origin of the barn is described in the
issue of symmetry magazine
ShedThe shed was devised to described incredibly small
areas. One shed is 10m, or 10b. A shed is to the barn what a barn
is to the square meter.
barns in Bosnian: Barn
barns in Bulgarian: Барн
barns in Danish: Barn (enhed)
barns in German: Barn
barns in Spanish: Barn
barns in French: Barn
barns in Korean: 바안
barns in Croatian: Barn
barns in Italian: Barn
barns in Japanese: バーン (単位)
barns in Norwegian: Barn (måleenhet)
barns in Polish: Barn
barns in Portuguese: Barn
barns in Russian: Барн
barns in Slovenian: Barn
barns in Serbian: Барн
barns in Swedish: Barn (enhet)
barns in Ukrainian: Барн