Shake (time)
Encyclopedia
A shake is an informal unit
Units of measurement
A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...

 of time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

 equal to 10 nanosecond
Nanosecond
A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns....

s, or 10−8 second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

s. It has applications in nuclear physics
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...

, helping to conveniently express the timing of various events in a nuclear explosion. The typical time required for one step in the chain reaction (ie. 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.

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 on how quickly a signal can progress through an IC.

Like many nuclear units, it is derived from Top Secret
Top Secret
Top Secret generally refers to the highest acknowledged level of classified information.Top Secret may also refer to:- Film and television :* Top Secret , a British comedy directed by Mario Zampi...

 operations of the Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...

 during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. 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.
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