Sepia Saturday #322: A Brief look at Nuclear Bomb Design

Quickly, I had to look up the differences between a lamb and a kid. In short, I learned a lamb's tail hangs down and a kid's tail turns up. The tiny lamb's tail is out of view in the prompt photo with the little kids, but I think the creature has a tell-tale wooly coat, another giveaway it's a baaaa baaaa. Even though it's getting a free drink, I bet that lamb would scurry away in a flash if the kids let it go. Have I jumped to a conclusion based on only a fleeting glance at the photo? I'm in such a hurry this week. 

In my hastily chosen photo below of an unknown young girl, the animal's tail is up, and it's coat is obviously goat hair. Speed was of the essence and I just had to go with the goat. As it's a fairly large animal, I'm surprised the little girl's mother(?) in the background let her handle it in this manner. She could get a sharp kick in the bare knee, uncovered as it is with that skimpy skirt. All danger aside, she looks as if she's telling the goat a short story or whispering sweet nano-nothings into her ear. 

As we're leaving for India tomorrow, my contribution this week is skimpy and brief. I could devote only a bit of time to it, perhaps 10 nanoseconds - a time short as two shakes of a lamb's tail, in fact.

From Wikipedia: A shake^[1] is an informal unit of time equal to 10 nanoseconds, or 10⁻⁸ seconds. It has applications in nuclear physics, helping to conveniently express the timing of various events in a nuclear explosion. The typical time required for one step in the chain reaction (i.e. the typical time for each neutron to cause a fission event which releases more neutrons) is of order 1 shake, and the chain reaction is typically complete by 50 to 100 shakes.^[2]

This is also applicable to circuits. Since signal progression in IC chips is very rapid, on the order of nanoseconds, a shake is good measure of how quickly a signal can progress through an IC.

Like many nuclear units, it is derived from Top Secret operations of the Manhattan Project during World War II. The word comes from the expression "two shakes of a lamb's tail," which indicates a very short time interval. For nuclear-bomb designers, 10 nanoseconds was a convenient specific interval to connect to this term.

It has been discussed at length that the oldest documented usage of the phrase "two shakes of a lamb's tail" can be found within the compiled works of Richard Harris Barham calledThe Ingoldsby Legends.

Unknown girl holding goat. Photo marked 1934 on the reverse.

Don't stand on ceremony. You're invited to butt in over at Sepia Saturday for more interesting tails tales.