Barn (unit)

The Barn b (English for barn) is a unit of area, which is used to specify cross sections in atomic, nuclear and particle physics.

The Barn is not an SI unit. It is in the countries of EU and Switzerland is a legal entity for the indication of cross sections, so no universal unit area.

A Barn is on the order of the geometrical cross section of heavy nuclei such as uranium.

Definition

To a number specified in barns are always three points: trapping particles to be captured, and the energy of the particles, for example, " Boron -10 has a thermal neutron cross section of Barn 3837 ". Because shows the cross section of an atom trapping for such a zoom flying particles as a circular area ( it hits this area or it flies past it and so escapes the capture? ), The size of the circular area for the definition of suitable.

Usual decimal parts

Small cross sections are in millibarn (mb), microbarn ( mB ), nanobarn ( nb) or Picobarn ( pb ) specified. For example, is

Shed

The Shed unit was used to describe very small cross sections, especially of neutrino reactions, thought, but could never take off properly. It is

Word origin

The term barn for the already usual cross section unit 10-24 cm2 was introduced in December 1942 by two scientists from Purdue University, at the American nuclear weapons development ( the Manhattan Project ) participated. It played a role, that a cross section of this size for nuclear reactions "as big as a barn" ( German: " big as a barn " ) appeared.