A unit of area for effective cross-section of atomic nuclei with respect to atomic projectiles; equal to 10−24 cm2. [fr. “big as the side of a b.” by humorous comparison with much smaller areas]
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bilateral acute retinal necrosis; Body Awareness Resource Network
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barn 'bärn n a unit of area equal to 10-24 square centimeters that is used in nuclear physics for measuring cross section
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bilateral acute retinal necrosis.
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(bahrn) [jocular “big as a barnâ€] a unit of area equal to 10−24 square centimeter, used in measuring nuclear scattering cross sections. Symbol b.Medical dictionary. 2011.