From L. atomus, from Gk. atomos "uncut," from → a- "not" + tomos "a cutting," from temnein "to cut."
Of or relating to an atom or atoms; of or employing nuclear energy.
Fr.: horloge atomique
A modern clock, in which the characteristic frequencies of certain atoms (most commonly chosen cesium 133) are utilized for precision time measurement. → atomic fountain clock.
Fr.: fontaine atomique
A gaseous ball of atoms, usually → cesium (133Cs), created by the → laser cooling technique and used in an → atomic fountain clock. The ball, typically a few millimeters in diameter and containing some 107 atoms, can be launched upward against gravity using a → laser beam. The launch velocity is chosen such that the atoms reach a height of about one meter before they turn back and fall down the same path they came up. The motion of the ball resembles that of the water in a pulsed fountain.
→ atomic; fountain, from M.E. fontayne from O.Fr. fontaine, from L.L. fontana, noun use of feminine of L. fontanus "of a spring," from fons "spring of water."
Favvâré, Pers. construction from Ar. faur "boiling, bubbling."
atomic fountain clock
sâ'at-e favvâre-ye atomi
Fr.: horloge à fontaine atomique
An → atomic clock based on the principle of the → atomic fountain. A ball of atoms, usually → cesium (133Cs), created by the → laser cooling technique, is trapped in the intersection region of six laser beams. The ball is thrown upward by a laser beam and passes twice through a cavity where the atoms interact with the → microwave radiation generated by an → oscillator. The ball reaches the summit of its trajectory (about 1 m above the cooling zone) and then due to gravity falls through the same microwave cavity. The microwave radiation causes the electrons of the cesium atoms to move between two specific → energy states as they pass through the cavity. The clock is based on a → hyperfine transition (9.192631770 GHz) between two energy states in the electronic → ground state of the atom. The upper hyperfine state can in principle radiate to the lower state by → spontaneous emission, but the process takes a very long time -- thousands of years. Selection and detection of the hyperfine state is performed via → optical pumping and laser induced resonance fluorescence. In a carefully controlled setup, a relative uncertainty of 10 -16 can be reached for the cesium clock. This means an accuracy of 1 sec every 300 million years. This fluorescence is measured by a detector. The entire process is repeated until the maximum fluorescence of the cesium atoms is determined. This determination is used to lock the oscillator to the atomic frequency of cesium, which is used to define the SI → second. The first atomic fountain for metrological use was developed at the Paris Observatory (A. Clairon et al. 1996, Proc. 5th Symp. Frequency Standards and Metrology, p. 45).
Fr.: chaleur atomique
hidrožen-e atomi (#)
Fr.: hydrogène atomique
atomic mass number (A-number)
adad-e jerm-e atomi (#)
Fr.: nombre de masse atomique
The total number of protons and neutrons in the nucleus of an atom. For example, Oxygen-16 has a mass number of sixteen, because it has eight protons and eight neutrons.
atomic mass unit (amu)
yekâ-ye jerm-e atomi (#)
Fr.: unité de masse atomique
A unit of mass used for atoms and molecules, equal to 1/12 of the mass of an atom of carbon-12 (including orbital electrons). It is equal to 1.660 33 × 10-24 g.
haste-ye atom (#)
Fr.: noyau atomique
The central part of the → atom. It is made up of → protons and, in most cases, → neutrons. The nucleus is surrounded by a swarm of fast-moving → electrons. Almost all of the mass (more than 99%) of an atom is contained in the dense nucleus. The number of protons in the nucleus (called → atomic number) determines the type of → chemical element. Atoms that differ only in the number of neutrons in their nuclei are called → isotopes.
adad-e atomi (#)
Fr.: nombre atomique
The number of → protons in an → atomic nucleus (symbol Z). Same as → Z-number. The atomic number is written as a subscript to the left of the → chemical element name. For example, the most common isotope of oxygen is shown as 816O, which has 8 → protons and its → mass number (A) is 16.
Fr.: proposition atomique
zamân-e atomi (#)
Fr.: temps atomique
Time measured using atomic clocks.
Fr.: transition atomique
vazn-e atomi (#)
Fr.: poids atomique
Fr.: FBF atomique
i) If t1, t2, ..., tn
are terms and P is a → predicate of arity n,
then P(t1, t2, ..., tn)
is an atomic wff.
Fr.: atome de Bohr
The simplest model of an atom according to which electrons move around the central nucleus in circular, but well-defined, orbits. For more details see → Bohr model.
diffuse atomic cloud
abr-e atomi-ye paxšidé
Fr.: nuage atomique diffus
A type of cloud in the → interstellar medium with low molecular content that is fully exposed to the → interstellar radiation field, and therefore nearly all its → molecules are quickly destroyed by → photodissociation. Hydrogen is mainly in → neutral atomic form (→ neutral hydrogen), and atoms with → ionization potentials less than that of hydrogen (most notably → carbon) are almost fully → ionized, providing abundant electrons. The paucity of molecules implies that very little chemistry occurs in such clouds. Many → sightlines with low → extinction seem to pass exclusively through → diffuse atomic gas. Such sightlines typically have a → column density, NH, less than about 5 × 1020 cm-2, and are sufficiently → optically thin to be observable by means of → visible and → ultraviolet → absorption line measurements. Diffuse atomic clouds typically have a fairly low → density (~ 10-100 cm-3), and → temperatures of 30-100 K (Snow & McCall, 2006, ARA&A 44, 367).
atom-e barangixté (#)
Fr.: atome excité
An atom in which one or more of its bound electrons are at → energy levels higher than their normal level.
Between atoms; relating to the interaction of different atoms.