The barn is an area of 10 exp-28 m exp2: about the size of the nuclues of a uranium atom. So named by nuclear physicists because for them it is as big as a barn. They (and I) should get out more. MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.