barn

1. A large farm building used for storing farm products and sheltering livestock.
2. A large shed for the housing of vehicles, such as railroad cars.
3. A particularly large, typically bare building: lived in a barn of a country house.
4. (Abbr. b) Physics. A unit of area equal to 10 ^-24 square centimeters, used to measure cross sections in nuclear physics.

[Middle English bern, from Old English berærn : bere, barley + ærn, house.]

For more information on barn, visit Britannica.com.

[uncommon; prob. from the nuclear military] An unexpectedly large quantity of something: a unit of measurement. “Why is /var/adm taking up so much space?” “The logs have grown to several barns.” The source of this is clear: when physicists were first studying nuclear interactions, the probability was thought to be proportional to the cross-sectional area of the nucleus (this probability is still called the cross-section). Upon experimenting, they discovered the interactions were far more probable than expected; the nuclei were “as big as a barn”. The units for cross-sections were christened Barns, (10^-24 cm²) and the book containing cross-sections has a picture of a barn on the cover.

sub-atomic physics 10^-28m², being the order of magnitude of the cross-sectional area of the nucleus, hence of relevance in probabilistic studies for interactions. Now better expressed just as 100 fm². The 1978 decision of the CIPM considering it acceptable to continue to use the barn with the SI still stands, though it is deprecated by other authorities.

A farm building, most often rectangular (but occasionally circular or polygonal), for housing farm animals, storing farm equipment, threshing grain, and storing grain, hay, and other agricultural produce. Barn construction usually depends on such factors as the local climate and traditions, building materials available, the skills and time required for construction, and the cost. For some examples, see bank barn, basement barn, circular barn, connected barn, Connecticut barn, crib barn, double barn, Dutch barn, English barn, forebay barn, four-crib barn, German barn, hex barn, New England connected barn, octagon barn, Pennsylvania barn, Pennsylvania Dutch barn, potato barn, raised barn, round barn, side-hill barn, Sweitzer barn, Swiss barn, three-bay barn, tobacco barn, Yankee barn.

A building usually intended to house animals for long periods during the winter season. Marked by an infinite variety of designs and internal fittings, they usually contain a feed storage area, often as a haymow or loft in a top storey, and animal stalls and handling facilities such as a milking parlor on the ground floor.

• free stall b. — cattle are free to enter unoccupied stalls.
• b. itch — see sarcoptic mange.
• b. rat — a horse that shows eagerness or determination to return to the stable. See also agoraphobia.
• b. sheet — a sketchy method of recording events, especially reproductive ones, in the lives of the inmates of the barn. Fixed to the barn wall it does provide an opportunity to record events as they happen, but suffers the obvious disadvantage of exposure to disfiguring and obscuring materials, especially fly droppings and cow manure. Its design, aimed at encouraging maximum data storage in minimal space, is a test for farmer ingenuity. Called also shed sheet.

It has been suggested that Outhouse (unit) be merged into this article or section. (Discuss)

It has been suggested that Shed (physics) be merged into this article or section. (Discuss)

A barn (symbol b) is a unit of area. 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. A barn is defined as 10⁻²⁸ m² or 100 square femtometers (fm²) and is approximately the cross sectional area of a uranium nucleus. The barn is also the unit of area used in nuclear quadrupole resonance and nuclear magnetic resonance to quantify the interaction of a nucleus with an electric field gradient. While the barn is not an SI unit, it is accepted for use with the SI due to its continued use in particle physics.^[1] It is one of the very few units which are accepted to be used with SI units, and one of the most recent units to have been established (cf. the knot and the bar, other non-SI units acceptable in limited circumstances).^[2]

Contents 1 Commonly used prefixed versions 2 Conversions 3 Origin 4 Usage example 5 Related units 6 See also 7 References 8 External links

Commonly used prefixed versions

Conversion to SI units

Unit	Symbol	m2	cm2
barn	b	10−28	10−24
millibarn	mb	10−31	10−27
microbarn	μb	10−34	10−30
nanobarn	nb	10−37	10−33
picobarn	pb	10−40	10−36
femtobarn	fb	10−43	10−39

Conversions

Calculated cross sections are often written in units of ħ²c²/GeV² (approximately 0.3894 mb).

Origin

The etymology of the unit barn is clearly whimsical and jocular. 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." 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.^[3][4]

Usage example

As a simplified example, if a beamline runs for 8 hours (28,800 seconds) at an instantaneous luminosity of 300 × 10³⁰ cm⁻²s⁻¹ = 300 μb⁻¹s⁻¹, then it will gather data totaling an integrated luminosity of 8,640,000 μb⁻¹ = 8.64 pb⁻¹ during this period.

Related units

The "inverse femtobarn" (fb⁻¹) is a measurement of particle collision events per femtobarn. Over a period of time, two streams of particles with a cross-sectional area, measured in femtobarns, are directed to collide. The total number of collisions is directly proportional to the luminosity of the collisions measured over this time. Therefore, the collision count can be calculated by multiplying the integrated luminosity by the sum of the cross-section for those collision processes. This count is then expressed as inverse femtobarns for the time period (e.g., 100 fb⁻¹ in 9 months). Inverse femtobarns are often quoted as an indication of particle collider effectiveness.^[5][6]

The "shed" was devised to describe incredibly small areas, far tinier than a barn. One shed is 10⁻⁵² m², or 10⁻²⁴ b.^[7]

See also

• Orders of magnitude (area)

References

1. ^ "Chapter 4.1: Non-SI units accepted for use with the SI, and units based on fundamental constants". SI brochure (8th edition). BIPM. May 2006. http://www.bipm.org/en/si/si_brochure/chapter4/4-1.html. Retrieved 2009-03-13. 
2. ^ "Table 8. Other non-SI units". SI brochure (8th edition). BIPM. May 2006. http://www.bipm.org/en/si/si_brochure/chapter4/table8.html. Retrieved 2009-03-13. 
3. ^ Mike Perricone (February 2006). "Signal to Background". Symmetry Magazine 3 (1): 4. http://www.symmetrymagazine.org/cms/?pid=1000258. Retrieved 2009-03-13. 
4. ^ Doreen Wackeroth, Leila Belkora (ed.). "Cross Section". High Energy Physics Made Painless. Fermilab Science Education Office. http://ed.fnal.gov/painless/pdfs/cross.pdf. Retrieved 2009-03-13. 
5. ^ Kate Metropolis (July 21, 2004). "Understanding luminosity through 'barn', a unit that helps physicists count particle events". Stanford News Service. http://news-service.stanford.edu/news/2004/july21/femtobarn-721.html. Retrieved 2009-03-13. 
6. ^ Mason Inman, Emily Ball (April 16, 2004). "PEP-II's luminous life". SLAC. http://www2.slac.stanford.edu/tip/special/PEP-II-04-16-04.htm. Retrieved 2009-03-13. 
7. ^ Russ Rowlett (September 1, 2004). "Units: S". How Many? A Dictionary of Units of Measurement. University of North Carolina at Chapel Hill. http://www.unc.edu/~rowlett/units/dictS.html. Retrieved 2009-03-13. 

External links

• IUPAC citation for this usage of "barn"

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Dansk (Danish)
n. - lade

idioms:

• barn burner    sensation
• barn dance    folkedans

Nederlands (Dutch)
schuur, stal, groot huis, in een schuur opslaan

Français (French)
n. - (US) écurie, étable

idioms:

• barn burner    chose intéressante
• barn dance    bal campagnard folklorique, danse campagnarde ou paysanne

Deutsch (German)
n. - Scheune, Schuppen

idioms:

• barn burner    Schlager
• barn dance    ländlicher Tanz, Tanztreff

Ελληνική (Greek)
n. - (σιτ)αποθήκη, σιτοβολώνας, αχυρώνας, υπόστεγο, ντεπό

idioms:

• barn burner    ριζοσπαστική πτέρυγα του Δημοκρατικού Κόμματος (ΗΠΑ)
• barn dance    είδος λαϊκού χορού

Italiano (Italian)
fienile, granaio

idioms:

• barn burner    astro dell'occasione
• barn dance    danza campestre

Português (Portuguese)
n. - celeiro (m)

idioms:

• barn burner    um acontecimento espetacular (coloq.)
• barn dance    dança (f) rápida semelhante à polca, arrasta-pé (m)

Русский (Russian)
амбар, зернохранилище, конюшня

idioms:

• barn burner    сенсация
• barn dance    народные танцы в амбаре

Español (Spanish)
n. - granero, cobertizo, establo, cuadra, barnio

idioms:

• barn burner    que despierta interés y animación
• barn dance    baile popular que tiene lugar en un granero

Svenska (Swedish)
n. - lada, ladugård, stall

中文（简体）(Chinese (Simplified))
谷仓, 粮仓, 大车库, 大车棚, 马房, 牛舍

idioms:

• barn burner    使兴奋或使有兴趣的事情
• barn dance    谷仓舞会

中文（繁體）(Chinese (Traditional))
n. - 穀倉, 糧倉, 大車庫, 大車棚, 馬房, 牛舍

idioms:

• barn burner    使興奮或使有興趣的事情
• barn dance    穀倉舞會

한국어 (Korean)
n. - 헛간, 텅 빈 건물

日本語 (Japanese)
n. - 納屋, がらんとした建物, バーン
v. - 納屋にしまう

idioms:

• barn burner    白熱の試合
• barn dance    バーンダンス

العربيه (Arabic)
‏(الاسم) حظيرة للماشيه, مخزن للحبوب‏

עברית (Hebrew)
n. - ‮אסם, ממגורה, בניין גס‬

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