CESIUM CLOCK
A cesium clock is defined as a clock containing a cesium standard as a frequency-determining element. A cesium standard is a primary frequency standard in which electronic transitions between the two hyperfine ground states of cesium-133 atoms is used to control the output frequency.
What is Cesium?
Cesium is an alkali metal. Cesium is in the same group as lithium, sodium, potassium, and rubidium. While cesium is similarly reactive, it is to a much higher degree than these other metals due to its extreme electropositivity.
The role of Cesium in Clocks
While natural cesium consists of a number of radioactive isotopes, it also consists of a single stable isotope, Cs 133. Probably the best-known use of the cesium Cs 133 isotope is in Cesium beam atomic clocks, which are among the most accurate time measuring devices in existence.
Very accurate clocks can be constructed by locking an electronic oscillator to the frequency of an atomic transition. The frequencies associated with such transitions are so reproducible that the definition of the second is now tied to the frequency associated with a transition in cesium-133:
1 second = 9,192, 631,770 cycles of the standard Cs-133 transition
Cesium clocks define the second
In 1967, the 13th General Conference on Weights and Measures first defined the International System (SI) unit of time, the second, in terms of atomic time rather than the motion of the Earth. Specifically, a second was defined as the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of cesium-133 atoms in their ground state undisturbed by external fields.
The current time standard for the United States is a cesium atomic frequency standard at the National Institute of Standards and Technology in Boulder, Colorado.
Symmetricom's Cesium Standards
Symmetricom makes a number of cesium beam frequency and time standard instruments for commercial, military and space applications and designs and manufacturers the cesium beam clocks for the Global Positioning System (GPS) satellites. These cesium frequency and time standards have a legacy of dependability and reliability. The accuracy and stability of these instruments have been proven ideal for the most stringent applications in navigation, communications and timing. The ability of our cesium instruments to provide stand-alone dependability, ease of use, and ease of installation makes them the preferred choice in the critical time or frequency systems found in telecommunications timing, calibration and metrology laboratories, satellite tracking stations and spaced based master time standards.
For information on our cesium products, click here.
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