Unit used in nuclear physics to indicate ?activation cross-sections of particles for a certain reaction. Symbol:b. One barn is equal to 10-28 m; this is approx. the cross-section area of a nucleus of an atom
Winfried Koelzer, Nuclear Terms, Karlsruher Institut for Technologie KIT (Ed.), ISBN German print version 2001: 3-923704-32-1, Translation by Informationskreis KernEnergie (Berlin), Karlsruhe, Germany 2013. https://www.euronuclear.org/info/encyclopedia/pdf/ Nuclear_Glossary-%202013-02-13.pdf, (Nucl Sfty - Amer) {1011}