File:Nbs-1.jpg
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English: NBS-1, the first cesium 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. 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 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. |
| Date | circa 1952 |
| Source |
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| Author | National Institute of Standard and Technology - Physics Laboratory: Time and Frequency Division |
| Permission (Reusing this file) |
Product of US Government employee |
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This image is in the public domain in the United States because it is a work of the United States Federal Government, specifically an employee of the National Institute of Standards and Technology, under the terms of Title 17, Chapter 1, Section 105 of the US Code.
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 03:49, 19 January 2013 | | 516 × 648 (84 KB) | Chetvorno (talk | contribs) | Higher resolution color image |
| 15:50, 21 December 2008 |  | 425 × 498 (39 KB) | Coenen (talk | contribs) | {{Information |Description={{en|1=Atomic Clock NBS-1 (1952)}} |Source=http://tf.nist.gov/general/museum/nbs-1.jpg |Author=National Institute of Standard and Technology - Physics Laboratory: Time and Frequency Division |Date= |Permission= |other_versions= |
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