ion, ion- +
(Greek: ion, "going"; neuter present participle of ienai, "to go"; because an ion moves toward the electrode of an opposite charge)
2. The average time between the ionization of an atom or molecule and its recombination with one or more electrons, or its loss of excess electrons.
3. The average time interval under specified atmospheric conditions between the formation and destruction of an ion of any given type.
The mean life of small ions in clean air, for example, over the sea, is four to five minutes, but in polluted air it is generally less than a minute.
Large ions have mean lifetimes of as much as 15 to 20 minutes over the oceans, while in very polluted areas, lifetimes may approach an hour.
A magnified image of isotopic distributions on the sample surface is produced using synchronous scanning of the primary ion beam and an oscilloscope.
The field then forces the ions to a fluorescent screen, which shows an enlarged image of the tip, and individual atoms are made visible.
2. Movement of ions produced in an electrolyte, semiconductor, etc., by the application of an electric potential between electrodes.
2. A vacuum glow discharge technique of nitriding or the diffusion of nitrogen into alloy steel to form hard nitrides in the surface layer (typically 250µm).
Performed at between 500 and 750 degrees Centigrade from a gas, salt bath, or plasma glow discharge.
2. A positive ion and an equal-charge negative ion, usually an electron, that are produced by the action of radiation on a neutral atom or molecule.
3. A pair of ions of equal and opposite charge formed by photoionization or by the interaction of matter with any sufficiently energetic particles; such as, beta particles or alpha particles.
An ion pair, in the context of chemistry, consists of a positive ion and a negative ion temporarily bonded together by the electrostatic force of attraction between them.
Ion pairs occur in concentrated solutions of electrolytes (substances that conduct electricity when dissolved or molten).
Thus, in concentrated solutions of sodium chloride, some positive sodium ions, Na+, and some negative chloride ions, Cl-, are paired together.
Upon colliding, two oppositely charged ions stay together only for a short period of time. On the average, a certain population of these pairs exists at any given time, although the formation and dissociation of ion-pairs is continuous.
2. Vehicular motion caused by reaction from the high-speed discharge of a beam of electrically charged minute particles, usually positive ions, that are accelerated in an electrostatic field and ejected behind the vehicle.
3. A propulsor (mechanical device that gives propulsion), usually a small thruster, used to create vehicular motion by generating a high-velocity jet of ions in an electrostatic field, then ejecting the ions behind a vehicle.
4. Propulsion by the reactive thrust of a high-speed beam of similarly charged ions ejected by an ion engine.
2. A vacuum pump in which gas molecules are first ionized by electrons that have been generated by a high voltage and are spiraling in a high-intensity magnetic field, and the molecules are then attracted to a cathode, or propelled by electrodes into an auxiliary pump or an ion trap.
3. A pump that ionizes gas molecules wilth high-energy electrons in a high-intensity magnetic field and then deposits them onto a cathode or ejects them into an auxiliary pump or ion trap.
4. In medicine, a complex of proteins located in the cell membrane that is responsible for actively transporting ions across the membrane against a concentration gradient using energy rich ATP (adenosine triphosphate) molecules. Functions in maintaining osmotic balance in cells and in the conduction of nerve impulses.
Adenosine triphosphate (ATP) refers to a nucleotide present in all living cells which serves as an energy source for many metabolic processes and is required for ribonucleic acid synthesis.
2. A process based on bifunctional (two functional) ion-exchange resins containing both anion (negatively charged ion) and cation (positively charged ion) adsorption sites, which removes both kinds of ions from solutions.
The thrust is small (making such rocket unsuitable for launch from the ground), but the propulsion is very efficient, since the energy given to the ions comes from solar cells or a nuclear power source, and the acceleration can be maintained for quite some time.
Because of the separate power source, the energy each ion gets is more than the energy given to molecules in the jet of ordinary chemical rockets, which is limited by what the chemistry of the rocket fuel provides.
2. The movement of ions across energy-transducing cell membranes.
Transport can be active, passive or facilitated. Ions may travel by themselves (uniport), or as a group of two or more ions in the same (symport) or opposite (antiport) directions.3. Movement of salts and other electrolytes in the form of ions from place to place within living systems.
Ion transport may occur by any of several different mechanisms; including, electrochemical diffusion, active-transport requiring energy, or bulk flow as in the flow of blood in the circulatory system of animals, or the transpiration stream in the xylem tissue of plants.
The best-known system for transporting ions actively is the sodium/potassium (Na/K) exchange pump, which occurs in plasma membranes of virtually all cells.
2. A system that prevents an ion spot from forming on a cathode-ray tube screen, generally by using a magnetic field to divert the beam. 3. An arrangement whereby ions in the electron beam of a cathode-ray tube are prevented from bombarding (hitting with high-energy particles) the screen and producing an ion spot, usually employing a magnet to bend the electron beam so that it passes through the tiny aperture of the electron gun, while the heavier ions are less affected by the magnetic field and are trapped inside the gun.
A metal electrode, usually of titanium, into which ions from an ion pump are attracted or absorbed.