atomic clock

atomic clock
an extremely accurate electronic clock regulated by the resonance frequency of atoms or molecules of certain substances, as cesium.
[1935-40]

* * *

      type of clock that uses certain resonance frequencies of atoms (usually cesium or rubidium) to keep time with extreme accuracy. The electronic components of atomic clocks are regulated by the frequency of the microwave (electromagnetic radiation) electromagnetic radiation. Only when this radiation is maintained at a highly specific frequency will it induce the quantum transition (energy change) of the cesium or rubidium atoms. In an atomic clock these quantum transitions are observed and maintained in a feedback loop that trims the frequency of the electromagnetic radiation; like the recurrent events in other types of clocks (clock), these waves are then counted.

      In 1967 the 13th General Conference on Weights and Measures redefined the second, the unit of time in the International System of Units, in terms of the cesium standard so as to equal the second of Ephemeris Time. The conference defined the second as “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.”

 Until the 1990s the cesium beam atomic clock was the most accurate standard of atomic time and frequency. The principle underlying the cesium clock is that all atoms of cesium-133 are identical and, when they absorb or release energy, produce radiation of exactly the same frequency, which makes the atoms perfect timepieces. Since that time, laboratories around the world have steadily improved the accuracy of cesium fountain atomic clocks. These clocks get their name from the fountainlike motion of the constituent cesium gas. The timing process begins by introducing cesium gas into a vacuum chamber and directing six infrared lasers (laser) (located at right angles to one another) to compact and cool (slow down) the cesium atoms to a temperature near absolute zero. Then two vertical lasers are used to nudge the atoms up about a metre (creating a “fountain”) through a microwave-filled cavity. The microwave frequency is tuned to maximize the observed fluorescence, which occurs at the natural resonance frequency (9,192,631,770 Hz) of the cesium atom. Because the round-trip through the microwave cavity takes about a second, control of the microwave frequency has resulted in greater timekeeping accuracy. The best cesium fountain atomic clocks are now predicted to be off by less than one second in more than 50 million years.

Jonathan D. Betts
 

* * *


Universalium. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • atomic clock — n. an extremely accurate clock whose precision depends upon the very constant frequency at which atoms (or molecules) of certain substances, as of cesium, rubidium, or ammonia, absorb or emit electromagnetic radiation …   English World dictionary

  • Atomic clock — Nuclear clock redirects here. For the clock as a measure for risk of catastrophic destruction, see Doomsday Clock. For a clock updated by radio signals (commonly but inaccurately called an atomic clock ), see Radio clock. For the album by Zion I …   Wikipedia

  • atomic clock — noun a timepiece that derives its time scale from the vibration of atoms or molecules • Hypernyms: ↑timepiece, ↑timekeeper, ↑horologe • Hyponyms: ↑ammonia clock, ↑caesium clock * * * noun, pl ⋯ clocks [count] : a special kind of clock …   Useful english dictionary

  • atomic clock — atominis laikrodis statusas T sritis fizika atitikmenys: angl. atomic clock; atomic timing device vok. Atomuhr, f rus. атомные часы pranc. horloge atomique, f …   Fizikos terminų žodynas

  • atomic clock — atominis laikrodis statusas T sritis Standartizacija ir metrologija apibrėžtis Labai tikslus elektroninis laiko matuoklis. Atominio laikrodžio veikimas kontroliuojamas kai kurių medžiagų (amoniako, cezio) atomų molekulių savaisiais virpesiais.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • atomic clock — atominis laikrodis statusas T sritis Standartizacija ir metrologija apibrėžtis Laikrodis, kuriame laiko masteliui sudaryti naudojami atomų virpesiai. atitikmenys: angl. atomic clock vok. Atomuhr, f rus. атомные часы, m pranc. horloge atomique, f …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • Atomic Clock Ensemble in Space — is a project lead by the European Space Agency which will place an ultra stable atomic clock on the International Space Station. Operation in the microgravity environment of the ISS will provide a stable and accurate time base for different areas …   Wikipedia

  • Atomic Clock Ensemble in Space — (ACES) est un projet mené par l Agence spatiale européenne qui placera une horloge atomique ultra stable sur la Station spatiale internationale. Son fonctionnement dans l environnement de microgravité de l ISS va assurer un climat stable et une… …   Wikipédia en Français

  • Atomic Clock Assembly in Space — Externe Forschungsplattformen am Columbus Raumlabor Das Atomic Clock Ensemble in Space (kurz: ACES) ist eines der externen Experimentallabore, die am Columbus Raumlabor, dem Wissenschaftslabor der ESA für die Internationale Raumstation, befestigt …   Deutsch Wikipedia

  • Atomic Clock Ensemble in Space — Externe Forschungsplattformen am Columbus Raumlabor Das Atomic Clock Ensemble in Space (kurz: ACES) ist eines der externen Experimentallabore, die am Columbus Raumlabor, dem Wissenschaftslabor der ESA für die Internationale Raumstation, befestigt …   Deutsch Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”