caesium atomic clock

(noun)

A primary frequency standard in which electronic transitions between the two hyperfine ground states of caesium-133 atoms are used to control the output frequency.

Related Terms

Examples of caesium atomic clock in the following topics:

  • The Alkali Metals

    • The alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs),and francium (Fr).
    • It is predicted that the next alkali metal after ununennium would be unhexpentium (Uhp), an element that has not yet received even attempts at synthesis due to its extremely high atomic number.
    • Two of the most well-known applications of the pure elements are rubidium and cesium atomic clocks, of which cesium atomic clocks are the most accurate representation of time known as of 2012.

  • Quantum Numbers

    • This was in contrast to previous work that focused on one-electron atoms such as hydrogen.
    • The first quantum number describes the electron shell, or energy level, of an atom.
    • For example, in caesium (Cs), the outermost valence electron is in the shell with energy level 6, so an electron in caesium can have an n value from 1 to 6.
    • For example, the quantum numbers of electrons from a magnesium atom are listed below.
    • The relationship between three of the four quantum numbers to the orbital shape of simple electronic configuration atoms up through radium (Ra, atomic number 88).

  • Time

    • Today, the SI Unit of the second is defined in terms of radiation emitted by cesium atoms.
    • The second is now operationally defined 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."
    • It follows that the hyperfine splitting in the ground state of the cesium 133 atom is exactly 9,192,631,770 hertz .
    • In other words, cesium atoms can be made to vibrate in a very steady way, and these vibrations can be readily observed and counted.
    • NIST-F1 is referred to as a fountain clock because it uses a fountain-like movement of atoms to obtain its improved reckoning of time.

  • The Photoelectric Effect

    • The photoelectric effect has been demonstrated using light with energies from a few electronvolts (eV) to over 1 MeV in high atomic number elements.
    • All atoms have their electrons in orbitals with well-defined energy levels.
    • However, if the energy of the light is such that the electron is excited above energy levels associated with the atom, the electron can actually break free from the atom leading to ionization of the atom.
    • Typically, one photon is either energetic enough to cause emission of an electron or the energy is lost as the atom returns back to the ground state.
    • The photocathode contains combinations of materials, such as caesium, rubidium, and antimony, specially selected to provide a low work function, so when illuminated by even very low levels of light, the photocathode readily releases electrons.

  • Properties of Quartz and Glass

    • Each oxygen atom is shared between two tetrahedra, giving an overall formula of SiO2.
    • This is employed in many modern electronic devices (wristwatches, clocks, radios, computers, cellphones) to keep track of time or provide a stable clock signal for digital circuits.
    • Silicon atoms are grey, and oxygen atoms are red.

  • Fluorescence and Phosphorescence

    • Fluorescence occurs when an orbital electron of a molecule or atom relaxes to its ground state by emitting a photon of light after being excited to a higher quantum state by some type of energy.
    • Commonly seen examples of phosphorescent materials are the glow-in-the-dark toys, paint, and clock dials that glow for some time after being charged with a bright light such as in any normal reading or room light .

  • Dating Using Radioactive Decay

    • After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a "daughter" nuclide, or decay product.
    • This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time it takes for the parent atom to decay into the daughter atom(s).
    • Here, t is age of the sample; D is number of atoms of the daughter isotope in the sample; D0 is number of atoms of the daughter isotope in the original composition; N is number of atoms of the parent isotope in the sample at time t (the present), given by N(t) = Noe-λt; and λ is the decay constant of the parent isotope, equal to the inverse of the radioactive half-life of the parent isotope times the natural logarithm of 2.

  • Doping: Connectivity of Semiconductors

    • Electrons in free atoms have discrete energy values.
    • In the atomic lattice of a substance, there is a set of filled atomic energy "bands" with a full complement of electrons, and a set of higher energy unfilled "bands" which have no electrons.
    • When this occurs, an atom of dopant replaces an atom of silicon in the lattice, and therefore an extra valence electron is introduced into the structure.
    • When just a few atoms of the dopant replace silicon atoms in the lattice, an n-type semiconductor is created.
    • Electronic devices and instruments, such as digital alarm clocks, mp3 players, computer processors, and the electronics in cell phones, all take advantage of semiconductor technology.

  • Carbon Dating and Estimating Fossil Age

    • However, these "molecular clocks" are sometimes inaccurate and provide only approximate timing.
    • After one half-life has elapsed, one half of the atoms of the Lead-212 nuclide will have decayed into a "daughter" nuclide or decay product.