It's not often that I get to start out an episode by discussing a unit used in physics,

which on the surface doesn't sound like the most exciting hook for an episode intro, but in

this case, I just can't help myself.

We're all used to the usual units, meters, parsecs, seconds, jewels, Kelvin,

all those.

But here's one you probably haven't heard of yet.

The barn.

The barn is a unit of area.

It's equal to a square 10 femtometers on a side. And one femtometer is 10 to the minus

15 meters. That's a millionth of a billionth of a meter. So this is not a very large area at all.

But during the Manhattan Project work on the development of the atom bomb, a couple physicists over at Purdue University

were using early particle accelerators to measure the cross sections of some nuclear reactions,

as in how close to nuclei had to be to get them to do interesting things with each other.

And they kept encountering this area again and again,

10 femtometers on a side. Once you got to nuclei to within an area of around 10 femtometers on

a side, they started doing interesting things. Since this common area was cropping up so much

in their calculations, they wanted to simplify

their lives and create a new unit.

So they didn't have to keep writing 10 square femtometers.

They wanted to write something else.

So they tossed around names like, should we call it the Oppenheimer, and that's a little

too long.

...