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Name: Mathew A.
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 9/30/2003


Question:
How does an atomic clock measures the beats of a cesium atom?


Replies:
It is sort of like going into the bathroom and humming different pitches until you find the pitch that resonates. (In most bathrooms, there are three sets of pitches that will resonate: those with wavelengths equal to the distance between the walls, or between the floor and ceiling, and sub-multiples.) Everybody else with a bathroom of precisely the same dimensions will find the same pitches you found, and the group of you will then share a frequency standard.

In a Cesium clock, you tune a microwave oscillator around until it has just the right frequency to excite particular electrons of a Cesium atom from one well-defined energy level to another well-defined level. (The reason you use Cesium is that it has some very well-defined levels. Later, you will understand that this means the levels are relatively long lived -- i.e., not damped.) When you have tuned the oscillator to maximize the excitation of Cesium electrons, you know that the microwave frequency is the same as the microwave frequency of any other Cesium clock -- so you have a standard that someone else can duplicate. Now all you have to do is declare that umpty-ump cycles of such an oscillator is one second. You choose umpty-ump so that it agrees with all other (mostly less precise) definitions of a second.

Here is more detail: http://tycho.usno.navy.mil/cesium.html

Tim Mooney


Rather than try to answer this question directly, I would rather direct you to the NIST (National Institute of Science and Technology) web site that does a very thorough and professional job of explaining your inquiry and the whole history of time standards:

http://www.boulder.nist.gov/timefreq/cesium/fountain.htm

Vince Calder



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