You searched for: “ionization
1. The process of adding an electron to, or removing an electron from, an atom or molecule so as to give a negative or positive net charge.

The atom is then called an ion.

2. A process in which electrically neutral atoms or molecules are converted to electrically charged atoms or molecules (ions) by the removal or addition of negatively charged electrons.

It is one of the principal ways in which radiation transfers energy to matter, and hence of detecting radiation.

In general, ionization occurs whenever sufficiently energetic charged particles or radiant energy travels through gases, liquids, or solids.

A certain minimal level of ionization is present in the earth's atmosphere because of continuous absorption of cosmic rays from space and ultraviolet radiation from the sun.

3. The process by which a neutral atom, or a cluster of such atoms, becomes an ion.

This may occur, for instance, by absorption of light ("photoionization") or by a collision with a fast particle ("impact ionization").

Also, certain molecules (such as table salt or sodium chloride, NaCl) are formed by natural ions (like Na+ and Cl-) held together by their electric attraction, and they may fall apart when dissolved in water (which weakens the attraction), enabling the solution to conduct electricity.

4. Production of charged atoms or molecules in a gas by electric discharge or by irradiation.
Word Entries containing the term: “ionization
atmospheric ionization (s) (noun), atmospheric ionizations (pl)
The process by which neutral atmospheric molecules or atoms are rendered electrically charged chiefly by collisions with high-energy particles: Atmospheric ionization is the charging of neutral particles in the atmosphere through violent contact with charged particles.

Atmospheric ionization is the production of ions in the atmosphere by the loss of an electron from a molecule, typically, for example, by cosmic rays or cosmic radiation.

Cosmic rays and radioactive decay are the main sources of atmospheric ionization.

Radioactivity at the surface can also produce ions in the lowest layer of the atmosphere.

avalanche ionization, Townsend avalanche, Townsend ionization
A process occurring among gaseous ions in an ionization chamber radiation detector.

Given an adequate mean free path, a primary ion caused by the incident radiation can be accelerated by the applied voltage to the point where its collisions produce several other ions, where each secondary ion does the same thing, and so on, causing an "avalanche".

The multiplication of ions can be in the millions or more.

This entry is located in the following unit: ion, ion- + (page 1)
electron avalanche, avalanche effect, cascade, cumulative ionization
1. A chain reaction that starts when one free electron collides with one or more orbiting electrons and frees them.

The free electrons then free others in the same manner, etc.

2. The cumulative process in which an electron (or other charged particle) accelerated by a strong electric field collides with and ionizes gas molecules, thereby releasing new electrons which in turn have more collisions, so that the discharge is self-maintained.
This entry is located in the following unit: electro-, electr-, electri- (page 47)
ion concentration, ion density, ionization density
1. In atmospheric electricity, the number of ions per unit volume of a given sample of air; more particularly, the number of ions of given type (positive small ion, negative small ion, positive large ion, etc.) per unit volume of air.
2. The number of ions per unit volume.
3. The density of ions in a gas.
This entry is located in the following units: centro-, centr-, centri-, kentro- (page 7) ion, ion- + (page 2)
ion counter, ionization counter
1. An ionization chamber in which there is no internal amplification by gas multiplication; used for counting ionizing particles.
2. An apparatus that counts the number of unit charges of electricity that are contained in a sampled volume of the atmosphere.

The general procedure is to pass a sample of the atmosphere through a charged cylindrical condenser.

The change in the potential across the condenser is a measure of the ionic charge contained in the sample volume and the change in potential depends upon such factors as the polarizing potential of the condenser, the mobility and charge of the ions, volume and length of the condenser, and sample flow rate.

This entry is located in the following unit: ion, ion- + (page 2)
ion gauge, ionization gauge, ionization vacuum gauge
1. A device that determines the degree of vacuum in an electron tube by measuring the amount of ionization current in the tube.
2. A device; such as, a Geiger counter, that determines the amount of radiation in a medium by measuring the ionization generated by charged particles passing through a gaseous substance.
This entry is located in the following unit: ion, ion- + (page 2)
ion source, ion gun, ionization source
A device that ionizes gas molecules and then focuses, accelerates, and emits them as a narrow beam.
This entry is located in the following unit: ion, ion- + (page 3)
ionization arc-over
1. Arcing across terminals or contacts due to ionization of the adjacent air or gas.
2. Arcing across satellite antenna terminals as the satellite passes through the ionized regions of the ionosphere.
3. An electric spark which is created when ionized charges build up in a medium and produce forces on the electrons.
ionization chamber
1. A device that measures the intensity of ionizing radiation.
2. A device used to detect and measure ionizing radiation, consisting of a gas-filled tube with electrodes at each end between which a voltage is maintained.

Radiation that ionizes gas molecules in the tube causes a current between the electrodes, the strength of which is a function of the radiation's intensity.

3. A gas-filled enclosure fitted with electrodes between which electric current flows upon ionization of the gas by incident radiation, the electrodes being maintained at a potential difference just sufficient to collect ions thus produced without causing further ionization.
4. The device for the detection and measurement of ionizing radiation.

It consists basically of a sealed chamber containing a gas and two electrodes between which a voltage is maintained by an external circuit.

When ionizing radiation; such as, a photon, enters the chamber (through a foil-covered window), it ionizes one or more gas molecules.

The ions are attracted to the oppositely charged electrodes; their presence causes a momentary drop in the voltage, which is recorded by the external circuit.

The observed voltage drop helps identify the radiation because it depends on the degree of ionization, which in turn depends on the charge, mass, and speed of the photon.

Geiger-Müller counter

A Geiger-Müller counter results from the application of a still-higher voltage across the electrodes of a proportional counter.

Individual particles of various kinds and energies entering a Geiger-Müller counter produce essentially the same large output pulse, making the instrument an excellent counter of individual particles.

The mixture of gases within a Geiger counter quenches the avalanche of ions produced by a single particle of radiation so that the device can recover to detect another particle.

An additional significant increase in voltage causes a continuous current to flow through the gas between the electrodes, rendering the device useless for detecting radiation.

—Compiled from "ionization chamber", Encyclopædia Britannica; 2010;
Encyclopædia Britannica Online; May 22, 2010.
ionization coefficient, specific ionization
The number of ion pairs formed per unit distance along the track of an ion passing through matter.
ionization constant
1. Analog of the dissociation constant; used for the application of the law of mass action to ionization.
2. An equilibrium constant for the ionization of a weak electrolyte.
3. A constant that depends upon the equilibrium between the ions and the molecules that are not ionized in a solution or liquid.
ionization cross section
1. The cross section for a particle or photon to undergo a collision with an atom, and so removing or adding one or more electrons to the atom.
2. An area in which the probability that an atom or ion will undergo ionization when it collides with a particle or photon of sufficient energy is measured.
ionization current, gas current
1. A current produced in an ionized gas by an electric field.
2. A positive-ion current produced by collisions between electrons and residual gas molecules in an electron tube.
ionization degree
1. The fractional degree of ionization of acids, bases, or salts that has taken place in a solution or reaction mixture.
2. The proportion of potential ionization that has taken place for an ionizable material in a solution or reaction mixture.
ionization energy, ionization potential, ion potential
1. The amount of energy required to remove an electron from a specific atom or ion to an infinite point, generally expressed in electron volts and numerically equal to the ionization potential.
2. The energy required o remove completely the weakest bound electron from its ground state in an atom or molecule so that the resulting ion is also in its ground state.
3. Amount of energy required to remove an electron from an isolated atom or molecule.

There is an ionization potential for each successive electron removed, though that associated with removing the first (most loosely held) electron is most commonly used.

The ionization potential of an element is a measure of its ability to enter into chemical reactions requiring ion formation or donation of electrons and is related to the nature of the chemical bonding in the compounds formed by elements.

ionization front
1. In astrophysics, a region in space in which the interstellar gas, commonly hydrogen, changes from a mostly neutral state to a mostly ionized situation, because of the ultraviolet radiation from hot stars nearby.
2. A transition region that separates interstellar gas in which a given atomic species, usually hydrogen, is mostly ionized from interstellar gas in which it is essentially neutral.
ionization spectrometer, Bragg spectrometer, crystal spectrometer, crystal-diffraction spectrometer
An instrument for x-ray analysis of crystal structure and measuring wavelengths of X-rays and gamma rays, in which a homogeneous beam of X-rays is directed on the known face of a crystal and the reflected beam is detected in a suitably placed ionization chamber.
This entry is located in the following unit: ion, ion- + (page 7)
ionization techniques
A class of techniques in crystal spectroscopy wherein an ionization chamber (an X-ray detector) is appropriately placed to detect the reflected X-rays after undergoing Bragg scattering which is the scattering of X-rays or neutrons by the regularly spaced atoms in a crystal, for which constructive interference occurs only at definite angles called Bragg angles (angles between an incident X-ray beam and a set of crystal planes for which the secondary radiation displays maximum intensity as a result of constructive interference).

"Bragg scattering" and "Bragg angles" are named after, Sir William Henry Bragg (1862–1942), and his son, Sir William Lawrence Bragg (1890–1971); English physicists and Nobel prize winners in 1915.

ionization time
1. The amount of time it takes for a gaseous substance to ionize after an ionizing property has been applied to it.
2. Referring to a gas tube, the time interval between the initiation of conditions for and the establishment of conduction at some stated value of tube voltage drop.
ionizing radiation, ionization radiation
1. High-energy radiation capable of producing ionization in substances through which it passes.

It includes non-particulate radiation; such as. X-rays, and radiation produced by energetic charged particles; such as, alpha and beta rays, and by neutrons, as from a nuclear reaction.

2. Particulate or electromagnetic radiation that produces ionization in a medium through which it passes.
3. Any radiation; such as, a stream of alpha particles or x-rays, that produces ionization as it passes through a medium.
4. Particles or photons that have sufficient energy to produce ionization directly in their passage through a substance.
5. Particles that are capable of nuclear interactions in which sufficient energy is released to produce ionization.
6. Photons of high-energy electromagnetic radiation and particle forms of radiation that have sufficient energy to produce ions by removing electrons from atoms or molecules.
This entry is located in the following unit: ion, ion- + (page 7)
primary ionization (s) (noun), primary ionizations (pl)
The first of a process of changing the properties or characteristics of chemical matter through incident radiation: Jane and the students in the chemistry class were expected to write the formulas for primary ionization of specific chemical elements.
This entry is located in the following units: ion, ion- + (page 10) prim-, primi-, primo- (page 2)
secondary ionization
Ions produced by collisions between primary ions or electrons and other atoms in an absorber.
This entry is located in the following unit: ion, ion- + (page 10)
thermal ionization
Atoms with low ionization potentials can be ionized by contact with the heated surface of a metal, generally a filament, having a high work function (the energy required to remove an electron from its surface) in a process called thermal, or surface, ionization.

This can be a highly efficient method and has the experimental advantage of producing ions with a small energy spread characteristic of the filament temperature, typically a few tenths of an electron volt, as compared with beam energies of thousands of electron volts.

The filaments, generally made of platinum, rhenium, tungsten, or tantalum, are heated by current.

Surface ionization requires a nearby source of atoms, often another filament operating at lower temperatures.

Samples can also be loaded directly on the filament, a widely used and successful technique and one that has resulted in many interesting chemical treatments of the sample when it is deposited on the filament.

One such application changed lead from a difficult to an easy element to analyze, enabling important geochronological and environmental measurements.

A disadvantage of thermal ionization is the possible change in isotopic composition during the measurement. This effect is caused by Rayleigh distillation, wherein light isotopes evaporate faster than heavy ones.

Studies done on isotopes that come from radioactive decay; such as, those used in determining the ages of rocks, encounter this problem, but it is correctable using the measured values of the isotopes that are not radiogenic.

With few exceptions the use of a thermal source requires the chemical separation of the sample. Useful data are commonly obtained on extremely small (nanogram) samples.

—Compiled from "mass spectrometry", Encyclopædia Britannica; 2010;
Encyclopædia Britannica Online; May 22, 2010.