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Atomic Clocks

  • Published
    23rd Sep, 2022

Given the technological advances of the present, we need clocks that will keep time to a very high accuracy. The answer to this requirement is the ‘atomic clock’.


Atomic Clock:

  • An atomic clock is a clock that uses the resonance frequencies of atoms as its resonator.
    • A clock is simply an apparatus that counts a repetitive event, e.g. in a mechanical clock, a pendulum might swing once every second and by counting the number of swings, one knows how many seconds have passed.
  • Atomic clocks use atoms, more precisely the electronic transition from one state to another as their ‘pendulum’.
  • They take advantage of the fact that all atoms of a particular element (e.g. Caesium and Rubidium) have the same electron configuration. 
  • In 1945, Columbia University physics professor Isidor Rabi suggested that a clock could be made from a technique he developed in the 1930s called atomic beam magnetic resonance.
  • By 1949, the National Bureau of Standards (now the National Institute of Standards and Technology) announced the world’s first atomic clock using the ammonia molecule as the source of vibrations.
  • By 1952 it announced the first atomic clock using cesium atoms as the vibration source, NBS-1.
  • With an error of only 1 second in up to 100 million years, atomic clocks are among the most accurate timekeeping devices in history.

Types of Atomic Clocks:

The various types of atomic clocks include:

  • Cesium atomicclocks employ a beam of cesium atoms. The clock separates cesium atoms of different energy levels by magnetic field.
  • Hydrogen atomic clocksmaintain hydrogen atoms at the required energy level in a container with walls of a special material so that the atoms don't lose their higher energy state too quickly.
  • Rubidium atomic clocks, the simplest and most compact of all, use a glass cell of rubidium gas that changes its absorption of light at the optical rubidium frequency when the surrounding microwave frequency is just right.

Why Do We Need Atomic Clocks?

  • Some 400 atomic clocks around the world contribute to the calculation of International Atomic Time (TAI), one of the time standards used to determine Coordinated Universal Time (UTC) and local times around the world.
  • Satellite navigation systems like GPS, GLONASS, and Galileo also rely on precise time measurements to calculate positions accurately.

Important terms

  • Cesium 133 - An isotope of cesium used especially in atomic clocks and one of whose atomic transitions is used as a scientific time standard
  • SI Second (atomic second) - The interval of time taken to complete 9,192,631,770 oscillations of the cesium 133 atom exposed to a suitable excitation

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