Dead Programmer's Cafe

Q: What is measured in shakes?
A: Time. 1 shake = 10 nanoseconds.

This unit of time was definitely created by Manhattan Project scientists, but why it was chosen is not 100% clear.

Theory # 1 – Too morbid
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A shake is only 10 nanoseconds in time and arises from the theory of the chain reaction where one free neutron causes a fission that creates 2.5 to 3 new neutrons like a huge pyramid scheme and by the time the last layers of fissions occur they produce enough energy to “shake” the earth severely.

Theory # 2 – Too dry
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I like the term “shake” – 10 nanoseconds. I think it’s roughly the time it
takes the average 1 Mev neutron to cover a distace of one mean free path (13 cm?) in fissile materials at maximum normal densities

Theory # 3 – Oralloy? Pu plasma? Shoo – way over my head.
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a shake being roughly 10 ns – the time it takes neutrons in oralloy or Pu plasma to cover their Mean Free Path

Theory # 4 – Sounds just about right.
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The ‘shake’ is a defined unit of time. Scientists working on the Manhattan project
(to build the first atomic bomb) found that the detonation cycle for the ‘device’
lasted 30 billionths of a second, or 30 nanoseconds. A shake was defined as
10 nanoseconds so the detonation cycle of the atomic bomb could be said to take
‘three shakes of a lamb’s tail.’