Barn
Symbol: b
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process. A barn is defined as 10-28 m2 or 100 square femtometers (fm2) and is approximately the cross sectional area of a uranium nucleus.
1b = 0,0000000000000000000000000001m2
1b = 10-28m2
1m2 = 10,000,000,000,000,000,000,000,000,000b