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.
| Definition | Relation to SI units |
|---|---|
≡ 10−28 m2 |
| millibarn | board | section | attobarn | hide | zeptobarn | square chain (international) | barn |
|---|---|---|---|---|---|---|---|
| 1 | 1.2916692500052 × 10-29 | 3.8610215854245 × 10-38 | 1.0 × 1015 | 2.0 × 10-37 | 1.0 × 1018 | 2.4710538146717 × 10-34 | 0.001 |
| 7.74192 × 1028 | 1 | 2.9891720232629 × 10-9 | 7.74192 × 1043 | 1.548384 × 10-8 | 7.74192 × 1046 | 1.9130700948883 × 10-5 | 7.74192 × 1025 |
| 2.589988110336 × 1037 | 334 540 800 | 1 | 2.589988110336 × 1052 | 5.1799762 | 2.589988110336 × 1055 | 6 400 | 2.589988110336 × 1034 |
| 1.0 × 10-15 | 1.2916692500052 × 10-44 | 3.8610215854245 × 10-53 | 1 | 2.0 × 10-52 | 1 000 | 2.4710538146717 × 10-49 | 1.0 × 10-18 |
| 5.0 × 1036 | 64,583,462.500258 | 0.1930511 | 5.0 × 1051 | 1 | 5.0 × 1054 | 1,235.5269073 | 5.0 × 1033 |
| 1.0 × 10-18 | 1.2916692500052 × 10-47 | 3.8610215854245 × 10-56 | 0.001 | 2.0 × 10-55 | 1 | 2.4710538146717 × 10-52 | 1.0 × 10-21 |
| 4.0468564224 × 1033 | 52 272 | 0.0001563 | 4.0468564224 × 1048 | 0.0008094 | 4.0468564224 × 1051 | 1 | 4.0468564224 × 1030 |
| 1 000 | 1.2916692500052 × 10-26 | 3.8610215854245 × 10-35 | 1.0 × 1018 | 2.0 × 10-34 | 1.0 × 1021 | 2.4710538146717 × 10-31 | 1 |
| Symbol | Definition |
|---|---|
| ≡ | exactly equal |
| ≈ | approximately equal to |
| = | equal to |
| digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |
| 1 barns | = 1.0E-28 square meters |
| 2 barns | = 2.0E-28 square meters |
| 3 barns | = 3.0E-28 square meters |
| 4 barns | = 4.0E-28 square meters |
| 5 barns | = 5.0E-28 square meters |