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The main variety of atomic clock uses caesium atoms cooled to temperatures that approach absolute zero. The primary standard for the United States, the National Institute of Standards and Technology (NIST)'s caesium fountain clock named NIST-F2, measures time with an uncertainty of 1 second in 300 million years (relative uncertainty 10 −16 ...
NIST physicists Steve Jefferts (foreground) and Tom Heavner with the NIST-F2 cesium fountain atomic clock, a civilian time standard for the United States. NIST-F2 is a caesium fountain atomic clock that, along with NIST-F1, serves as the United States' primary time and frequency standard. [1] NIST-F2 was brought online on 3 April 2014. [1] [2]
In May 2013 the NIST-F1 cesium fountain clock reported a u B of 3.1 × 10 −16. However, that BIPM report and the other recent reports are based on an evaluation that dates to 2005. [ 4 ] It used a model developed by NIST [ 5 ] to evaluate Doppler frequency shifts, known as distributed cavity phase, some believe to be incorrect. [ 6 ]
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. The first caesium clock was built by Louis Essen in 1955 at the National Physical Laboratory in the UK [1] and promoted worldwide by Gernot M. R ...
Herschede Clock Company; Cincinnati, Ohio and Starkville, Mississippi (1885-1984) Hotchkiss and Benedict; Auburn, New York (ca. 1835) Howard Miller Clock Company; Zeeland, Michigan (1926–Present) Ingraham Company; Bristol, Connecticut (1958–1967) Ithaca Calendar Clock Company; Ithaca, New York (late 1800s)
Search. Search. Appearance. Donate; Create account; ... Cs fountain 4 × 10 −16 ... 18 cesium atomic clocks and 4 hydrogen maser clocks Cs, H
The idea of the atomic fountain was first proposed in the 1950s by Jerrold Zacharias. [6] [7] Zacharias attempted to implement an atomic fountain using a thermal beam of atoms, under the assumption that the atoms at the low-velocity end of the Maxwell–Boltzmann distribution would be of sufficiently low energy to execute a reasonably sized parabolic trajectory. [8]
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 ...