Ashake is an informalmetric unit oftime equal to 10nanoseconds, or 10−8seconds.[1] It was originally coined for use innuclear physics, helping to conveniently express the timing of various events in a nuclear reaction.
Like many informal units having to do with nuclear physics, it arose fromtop secret operations of theManhattan Project duringWorld War II. The word "shake" was taken from theidiomatic expression"in two shakes of a lamb's tail", which indicates a very short time interval.
The phrase "a couple of shakes," in reference to the measurement of time, may have been popularized byRichard Barham'sIngoldsby Legends (1840);[2] however, the phrase was already part of vernacular language long before that.[3]
For nuclear-bomb designers, the term was a convenient name for the short interval, rounded to 10 nanoseconds, which was frequently seen in their measurements and calculations: The typical time required for one step in a chain reaction (i.e. the typical time for each neutron to cause a fission event, which releases more neutrons) is of the order of 1 shake, and a chain reaction is typically complete by 50 to 100 shakes.[4]
I'll be back in a couple of shakes.Also on page 212 ("A Row in an Omnibus") "in a brace of shakes" and on page 247 ("The Lay of St. Alois") "in a couple of shakes." But the phrase appeared in print before Barham; see for exampleJames Edward Alexander (1833).Transatlantic Sketches. p. 284.
The period, 10−8 seconds, turns out to be a convenient unit of time, and it was defined during the Manhattan Project as one 'shake'.
