Built on Facts: Failures of Cuteness in Physics
There’s a unit of cross-sectional area used in nuclear physics equal to a trillionth of a trillionth of a square centimeter. It’s roughly the cross-section of a heavy atomic nucleus, and it’s used to discuss interactions with incoming particles. You could say in some ways it’s a measure of how easy it is to hit a nucleus with a projectile like a neutron. A big nucleus is as easy to hit as the broad side of a barn. And the unit is called the barn, for exactly that reason. I have no evidence, but I blame Feynman anyway.
Don’t blame Feynman!
The “barn” was invented at Purdue University in 1942 by physicists M. G. Holloway and C. P. Parker. It made its first appearances in internal technical reports at Los Alamos in 1943. The following explanation for the origin of the term comes from a report by Holloway and Baker (1944).
“Some time in December of 1942, the authors, being hungry and deprived temporarily of domestic cooking, were eating dinner in the cafeteria of the Union Building of Purdue University. . . In the course of the conversation it was lamented that there was no name for the unit of cross sections of 10^-24 cm2 . . . The tradition of naming a unit after some great man closely associated with the field ran into difficulties . . . The “Oppenheimer” was discarded because of its length . . . The “Bethe” was thought to lend itself to confusion because of the widespread use of the Greek letter. Since John Manley was directing the work at Purdue, his name was tried, but Manley was thought to be too long. The “John” was considered, but was discarded because of the use of the term for purposes other than as the name of a person. The rural background of one of the authors then led to the bridging of the gap between the “John” and the “barn.” This immediately seemed good, and further it was pointed out that a cross section of 10^-24 cm2 for nuclear processes was really as big as a barn. Such was the birth of the barn.”
Another unit of cross section used in the late 1940s and 1950s was “the shed” = 10^^-48 cm2.
Michael A. Gottlieb
Physics Department
California Institute of Technology
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http://www.feynmanlectures.info
Sources:
http://www.orau.org/PTP/articlesstories/names.htm
http://news-service.stanford.edu/news/2004/july21/femtobarn-721.html
“Radiation Protection and Dosimetry” By Michael G. Stabin, Springer, 2007 (page 63)