File:Nbs-1.jpg: Difference between revisions

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|Description={{en|1=NBS-1, the first cesium [[:en:atomic clock|atomic clock]] built by the US National Bureau of Standards (now [[National Institute of Standards and Technology]] (NIST) in 1952. It was begun in 1950 but the project was delayed and it wasn't operating reliably enough to be used as a frequency standard until 1958. Meanwhile, Louis Essen at the National Physics Laboratory in Britain completed the first working cesium atomic clock in 1955. NBS-1 is an atomic oscillator producing a microwave signal at a frequency of 9,192,631,770 Hz (9.19 GHz), the frequency of the transition between the two hyperfine states of cesium 137. It has a resonance width of 300 Hz.}}<br />

It consists of a vacuum chamber containing at one end an oven to evaporate cesium atoms, and a magnet filter to select a beam of cesium atoms in a single state. The atom beam passes through two arms of a U shaped [[:en:microwave cavity|microwave cavity]] called a Ramsey cavity, which contains microwaves generated by an oscillator. The first arm sets the atoms oscillating. The second arm "interrogates" the atoms. If the frequency of the microwave signal is exactly equal to the transition frequency of the atoms, they will "flip" to the other state. The atomic beam then passes through a second magnetic filter which separates out the atoms which have "flipped", and a detector creates a signal proportional to the number of atoms. The detector signal is applied to a servo system in a feedback loop, which adjusts the frequency of the oscillator until the maximum number of cesium atoms "flip". Then the superprecise 9.1 GHz microwave signal from the oscillator is divided down in frequency by digital dividers to a 1 Hz clock signal, which can be used to run a digital clock.

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*Original B&W image from: http://tf.nist.gov/general/museum/nbs-1.jpg

*Color image downloaded [[2013-01-18]] from: [http://tf.nist.gov/timefreq/general/pdf/2039.pdf Lombardi, M. A.; Heavner, T.P; Jefferts, S.R. (December 2007) ''NIST primary frequency standards and the realization of the SI second'', Journal of Measurement Science, Vol.2, No.4, p.82, fig.9] on [http://tf.nist.gov/timefreq/cesium/atomichistory.htm ''A brief history of atomic clocks at NIST''], Time and Frequency Division, NIST website

*Disclaimer on first page: "This paper is a contribution of the United States government and is not subject to copyright"

|Date= {{other date|~|1952}}

|Permission= Product of US Government employee

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[[Category:NBS-1 atomic clock]]