barn

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barn,

abbr. b, in physics, unit of nuclear cross section, i.e., the effective target presented by a nucleusnucleus,
in physics, the extremely dense central core of an atom. The Nature of the Nucleus
Composition

Atomic nuclei are composed of two types of particles, protons and neutrons, which are collectively known as nucleons.
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 for collisions leading to nuclear reactions; it is equal to 10−24 square centimeters. The barn is approximately the size of the geometric cross section of an atomic nucleus; the term was coined because an effective cross section that large would present a target "as big as a barn," i.e., an easy target for nuclear bombardment. In practice, effective cross sections of nuclei for many reactions are measured in millibarns (10−3 barn) because, for most interactions, only a small fraction of collisions cause reactions.

Barn

A building for housing animals and storing farm equipment, hay, and other agricultural produce.

Barn

 

a unit of effective cross-sectional area of nuclear processes. One barn = 10–24 cm2 = 10–28 m2. Selection of this unit is related to the fact that the geometric cross sections of atomic nuclei are on the order of 10–24 cm2 in size. The magnitudes of the majority of cross sections of nuclear reactions usually lie in the range between 10–22 cm2 and 10–27cm2. For this reason fractional and multiple barn units are used, such as millibarn (10–27 cm2), microbarn (10–30 cm2), and megabarn (10–18 cm2).

barn

[′bärn]
(agriculture)
A farm building used for storage of agricultural products and equipment or for housing farm animals.
(nuclear physics)
A unit of area equal to 10-24 square centimeter; used in specifying nuclear cross sections. Symbolized b.

barn

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.

barn

1
US and Canadian a large shed for sheltering railroad cars, trucks, etc.

barn

2
a unit of nuclear cross section equal to 10--28 square metre.