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A caesium atomic fountain used as part of an atomic clock. The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency.
A caesium atomic clock from 1975 (upper ... NIST developed a series of seven caesium-133 microwave clocks named NBS-1 to NBS-6 and NIST-7 after the agency ...
Like other caesium atomic clocks, the clock keeps time by a precise 9.192631770 GHz microwave signal emitted by electron spin transitions between two hyperfine energy levels in atoms of caesium-133. A feedback mechanism keeps a quartz crystal oscillator on the chip locked to this frequency, which is divided down by digital counters to give 10 ...
18 cesium atomic clocks and 4 hydrogen maser clocks Cs, H National Institute of Information and Communications Technology; Koganei, ...
Caesium is widely used in highly accurate atomic clocks. In 1967, the International System of Units began using a specific hyperfine transition of neutral caesium-133 atoms to define the basic unit of time, the second.
Due to the accuracy of hyperfine structure transition-based atomic clocks, they are now used as the basis for the definition of the second. One second is now defined to be exactly 9 192 631 770 cycles of the hyperfine structure transition frequency of caesium-133 atoms.
The Bulletin of the Atomic Scientists set the clock to 89 seconds before midnight - the theoretical point of annihilation. That is one second closer than it was set last year.
Louis Essen (right) and Jack Parry (left) standing next to the world's first caesium-133 atomic clock. Essen earned his PhD (1941) and Doctor of Science (1948) from the University of London before becoming interested in the possibility of using the frequency of atomic spectra to improve time measurement.