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A barn (symbol: b) is a unit of area equal to 10−28 m2 (100 fm2). Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is also used in all fields of high-energy physics to express the cross sections of any scattering process, and is best understood as a measure of the probability of interaction between small particles.
The virgate, yardland, or yard of land (Latin: virgāta [terrae]) was an English unit of land. Primarily a measure of tax assessment rather than area, the virgate was usually (but not always) reckoned as 1⁄4 hide and notionally (but seldom exactly) equal to 30 acres. It was equivalent to two of the Danelaw's oxgangs.