Glossary of Terms

ACTIVITY (A) - The amount of a radionuclide defined in terms of its transition rate or disintegration rate. The activity of a radionuclide is equal to the product of the decay constant and the number of atoms of that radionuclide (A = N ). The traditional unit of activity is the curie (Ci) and the SI unit of activity is the becquerel (Bq).

AIRBORNE RADIOACTIVITY AREA - Any room, enclosure, or operating area in which airborne radioactive material, composed wholly or partly of licensed material, exists in concentrations:

ALARA - As Low As is Reasonably Achievable means making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical consistent with the purpose for which the activity is undertaken, the economics of improvements in relation to the state of technology, the economics of improvements in relation to benefits to the public health and safety and other societal and socioeconomic considerations, and in relation to utilization of nuclear energy and licensed or registered sources of radiation in the public interest.

ALARA PROGRAM - A program designed to maintain effluents to unrestricted areas, occupational doses, and doses to the general public As Low As is Reasonably Achievable.

ALPHA PARTICLE () - A positively charged particle emitted by certain radioactive materials. It is made up of two neutrons and two protons bound together, hence is identical to the nucleus of a helium atom. It is the least penetrating of the three common types of radiation (alpha, beta, gamma) emitted by radioactive material, being stopped by a sheet of paper.

ANNIHILATION PHOTONS - Photons that are created when a positive electron (positron) and a negative electron interact, resulting in their mutual annihilation. In this reaction, the rest mass of the positive electron and the negative electron are converted into two photons with an energy of 0.511 MeV each.

ANNUAL LIMIT ON INTAKE (ALI) - The derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. ALI is the smaller value of intake of a given radionuclide in a year by the reference man that would result in a committed effective dose equivalent of 0.05 Sv (5 rem) or a committed dose equivalent of 0.5 Sv (50 rem) to any individual organ or tissue.

ATOMIC MASS - The mass of a neutral atom of a nuclide, usually expressed in terms of "atomic mass units" or amu. Also referred to as atomic weight.

ATOMIC MASS NUMBER (A) - A number equal to the number of nucleons (neutrons plus protons) within the nucleus of an atom.

ATOMIC MASS UNIT (amu) - The atomic mass unit is one twelfth the mass of one neutral atom of carbon-12; 1 amu = 1.6605655 x 10-24 gram.

ATOMIC NUMBER (Z) - The number of protons in the nucleus of a neutral atom of a nuclide. The "effective atomic number" is calculated from the composition and atomic numbers of a compound or mixture. An element of this atomic number would interact with photons in the same way as the compound mixture.

BACKGROUND RADIATION - Radiation arising from radiation sources other than the one directly under consideration. Background radiation due to cosmic rays and natural radioactivity is always present. There may also be background radiation due to the presence of radioactive substances in other parts of the building, in the building material itself, etc.

BECQUEREL (Bq) - The SI unit of activity. 1 Bq = 1/s, read as one nuclear transformation per second (ntps). Also may be defined as 1 disintegration per second (dps). The becquerel equals approximately 2.7 x 10-11 curie. See "activity" and "curie."

BETA PARTICLE (ß- or ß+) - An elementary particle emitted from the nucleus of an atom during radioactive decay, which has one negative or one positive unit of elementary electrical charge (1.6022 x 10-19 coulomb) and a rest mass of 0.00054858 atomic mass unit (9.1095 x 10-28 gram). Once emitted, a negatively charged beta particle is identical to a negatively charged electron. Once emitted, a positively charged beta particle (sometimes called a positron) is identical to a positively charged electron. Beta radiation on or near the surface of the body may cause skin burns. Beta emitters can be harmful to internal tissues if they enter the body by ingestion, inhalation, absorption through the skin, or injection. (See "annihilation photons" and "electron.")

BRACHYTHERAPY - A method of radiation therapy in which sealed sources are used to deliver a radiation dose at a distance of less than 6 centimeters, by surface, intracavitary, or interstitial application.

BREMSSTRAHLUNG - Electromagnetic radiation emitted (as photons) when a fast moving charged particle (usually an electron) loses energy upon being accelerated and deflected by the electric field surrounding a positively charged atomic nucleus. X-rays produced in ordinary X-ray machines are bremsstrahlung. (In German, the word means "braking radiation.")

COMMITTED DOSE EQUIVALENT (H[T,50]) - The dose equivalent to organs or tissues of reference (T) that will be received from a intake of radioactive material by an individual during the 50-year period following the intake.

COMMITTED EFFECTIVE DOSE EQUIVALENT (H[E,50]) - The sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent to each of these organs or tissues (H[E,50]) = SUM w[T]H[T,50]).

CURIE (Ci) - The traditional unit of activity. One curie is equal to 3.7 x 1010 nuclear transformations per second (also referred to as disintegrations per second or dps). Equal to 2.22 x 1012 disintegrations per minute (dpm). Several fractions of the curie are in common usage. One curie equals 3.7 x 1010 becquerels. See "activity" and "becquerel."

DECAY, RADIOACTIVE - Disintegrations of the nucleus of an unstable nuclide by spontaneous emission of charged particles and/or photons.

DECAY CONSTANT (  ) - The fraction of the number of atoms of a radionuclide which decay in unit time; in the following equation;

N = No e - t

where No is the initial number of atoms present, and N is the number of atoms present after some time, t.  Sometimes called the disintegration constant.  The following relationship exists between a radionuclide's decay constant and half-life (T);

           ln 2
  =  ----------

           T1/2

DECLARED PREGNANT WOMAN - Any woman who has voluntarily informed her employer, in writing, of her pregnancy. At UIC, a form must be used to make the declaration. Forms are available from the Radiation Safety Section (voice phone - 312 996-7429).

DEEP DOSE EQUIVALENT (H[d]) - The dose equivalent at a tissue depth of 1 centimeter (1000 milligrams per square centimeter) from external whole-body exposure.

DERIVED AIR CONCENTRATION (DAC) - The concentration of a given radionuclide in air which, if breathed by the reference man for a working year of 2,000 hours under conditions of light work would result in an intake of one ALI. For purposes of this definition, the condition of light work is an inhalation rate of 1.2 cubic meters of air per hour for 2,000 hours in a year.

DOSE - A general term denoting the quantity of radiation or energy absorbed. For special purposes it must be appropriately qualified. If unqualified, it refers to absorbed dose.

DOSE, ABSORBED (D) - The energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest. The traditional unit of absorbed dose is the rad and the SI unit is the gray (Gy). An absorbed dose of one rad equals 0.01 gray.

DOSE EQUIVALENT (H[T]) - A quantity used for radiation protection purposes that expresses the biological effectiveness of exposure from different types of radiation on a common scale for all radiations. The dose equivalent is calculated by multiplying the absorbed dose (D) in tissue by the quality factor (Q) and other modifying factors, and is expressed numerically in units of rems or sieverts (Sv). See "relative biological effectiveness" and "dose, absorbed."

EFFECTIVE DOSE EQUIVALENT (H[E]) - The sum of the products of the dose equivalent to each organ or tissue (H[T]) and the weighting factor (W[T]) applicable to each of the body organs or tissues that are irradiated (H[E] = SUM w[T]H[T]).

ELECTRON (e- or e+) - A stable elementary particle which has one negative or one positive unit of elementary electrical charge (1.6022 x 10-19 coulomb) and a rest mass of 0.00054858 atomic mass unit (9.1095 x 10-28 gram), approximately 1/1836 of the mass of a proton. Electrons are usually negatively charged but may also be positively charged. (See "positron" and "beta particle.")

ELECTRON, SECONDARY - An electron ejected from an atom, molecule, or surface as a result of an interaction with a charged particle or photon.

ELECTRON, VALENCE - Electron which is gained, lost, or shared in a chemical reaction.

ELECTRON CAPTURE (EC) - A mode of radioactive decay in which an orbital electron is captured by the nucleus of the atom. A new nuclide is formed with the mass number unchanged but which has one additional neutron and one fewer proton.

ELECTRON VOLT (eV) - A unit of energy equivalent to the energy gained by an electron in passing through a potential difference of one volt. Larger multiple units of the electron volt are frequently used: keV for thousand or kilo electron volts; MeV for million or mega electron volts. The electron volt is a unit of energy or work, not voltage. 1 eV = 1.6 x 10-10 erg.

EXPOSURE (E or X) - Exposure is the total negative or positive charge liberated by photons (x rays and gamma rays) as the result of interactions in air. The traditional unit of exposure is the roentgen and the SI unit of exposure is the coulomb/kg of air.

EXPOSURE RATE - The exposure per unit of time, such as roentgen per minute (R/min) and milliroentgen per hour (mR/h).

EXTERNAL DOSE - That portion of the dose equivalent received from any source of radiation outside the body.

GAMMA RAYS (GAMMA ) - High energy, short wavelength electromagnetic radiation (photons). Gamma radiation frequently accompanies alpha and beta emissions and always accompanies fission. Except for those of very low energy, gamma rays are very penetrating and are best stopped or shielded against by dense materials, such as lead or depleted uranium. Gamma rays are essentially similar to x rays, but are usually more energetic, and are nuclear in origin. (Compare "x rays." See "decay, radioactive" and "photon.")

GEIGER-MÜLLER COUNTER - An electronic instrument used to detect or measure ionizing radiation which employs a Geiger-Müller tube as the detector. These instruments are sometimes referred to as Geiger Counters or G-M Counters.

GEIGER-MÜLLER TUBE - A radiation detector which consists of a gas filled (Geiger-Müller) tube containing electrodes, between which there is an electrical voltage but no current flowing. When ionizing radiation passes through the tube, the gas is ionized and a short, intense pulse of current passes from the negative electrode to the positive electrode which can then be measured or counted. The number of pulses per second is directly proportional to the intensity of radiation. It is also often known as Geiger tube or a GM tube; it was named for Hans Geiger and W. Müller who invented it in the 1920s.

GRAY (Gy) - The basic SI unit of absorbed dose of ionizing radiation. A dose of one gray means the absorption of 1 joule of radiation energy per kilogram of absorbing material. An absorbed dose of one gray equals 100 rads.

HALF-LIFE, BIOLOGICAL(Tb)  - The time required for a biological system, such as a man or an animal, to eliminate half the amount of a substance that has entered it (e.g. radioactive material) by biological processes.

HALF-LIFE, EFFECTIVE (Te) - The time required for a radionuclide contained in a biological system, such as a man or animal, to reduce its activity by half as a combined result of radioactive decay and biological elimination. Expressed mathematically,

 1             1            1
-----  =  -----  +   -----,   or

Te           T         Tp

            TB x Tp
Te =   ------------- .

            TB + Tp

HALF-LIFE, PHYSICAL (Tp) - The time in which half the atoms of a particular radioactive substance disintegrate to another nuclear form. Half-lives of various radionuclides range from millionths of a second to billions of years.

HIGH RADIATION AREA - Any area, accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 1 mSv (0.1 rem) in 1 hour at 30 centimeters from any source of radiation or from any surface that the radiation penetrates.

IDNS - The Illinois Department of Nuclear Safety, the agency issuing the radioactive material license to UIC.

INSPECTION - An official examination or observation including, but not limited to, tests, surveys, and monitoring to determine compliance with rules, regulations, orders, requirements, and conditions of the Department.

INTERNAL DOSE - That portion of the dose equivalent received from radioactive material taken into the body.

ION - An atom or molecule that has lost or gained one or more electrons. By this ionization it becomes electrically charged. Examples: an alpha particle, which is a helium atom minus two electrons; a proton, which is a hydrogen-1 atom minus its electron.

IONIZATION - The process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules, thereby creating ions. High temperatures, electrical discharges, or nuclear radiation can cause ionization.

IONIZATION CHAMBER - An instrument that detects and measures ionizing radiation by measuring the electrical current that flows when radiation ionizes gas in a chamber, making the gas the conductor of the electricity.

IONIZING EVENT - Any occurrence in which an ion or group of ions is produced; for example, by passage of a charged particle through matter.

IONIZING RADIATION - Any radiation displacing electrons from atoms or molecules, thereby producing ions. Examples: alpha, beta, gamma radiation and short wave ultraviolet light.

ION PAIR - A closely associated positive ion and negative ion (usually an electron) having charges of the same magnitude and formed from a neutral atom or molecule by radiation.

ISOTOPE - One of two or more atoms with the same atomic number (the same chemical element) but with different atomic weights. An equivalent statement is that the nuclei of isotopes have the same number of protons but different numbers of neutrons. Thus, C-12, C-13, and C-14 are isotopes of the element carbon, the number following the dash denoting their differing atomic mass numbers. Isotopes usually have very nearly the same chemical properties, but somewhat different physical properties. (See "nuclide," "radionuclide," and "radioisotope.")

keV - One thousand (or 103) electron volts. (See "electron volt.")

LICENSE - Any written document issued by the Illinois Department of Nuclear Safety, the Nuclear Regulatory Commission, or an Agreement state which grants authorization to possess and/or use radioactive material.

LICENSED MATERIAL - Radioactive material received, possessed, used, transferred or disposed of under a general or specific license.

LICENSEE - Any person who is licensed by the Illinois Department of Nuclear Safety, the Nuclear Regulatory Commission, or an Agreement state.

LINEAR ENERGY TRANSFER (LET) - The average loss in energy per unit of path traveled by the incident radiations. LET is usually expressed in keV/micron.

MeV - One million (or 106) electron volts. (See "electron volt.")

MICROCURIE (µCi) - One millionth of a curie (3.7 X 104 disintegrations per second).

MILLICURIE (mCi) - One thousandth of a curie (3.7 x 107 disintegrations per second).

MINOR - An individual less than 18 years of age.

NANOCURIE (nCi) - One thousandth of a microcurie (37 disintegrations per second).

NEUTRON - An uncharged elementary particle with a rest mass of 1.008665012 atomic mass units (1.67495 x 10-24 gram), slightly greater than the rest mass of a proton. Neutrons are found in the nucleus of every atom heavier than hydrogen-1.

NONSTOCHASTIC EFFECT (deterministic effect) - A health effect, the severity of which varies with the dose and for which a threshold is believed to exist.

NUCLIDE - A general term applicable to all atomic forms of the elements.

OCCUPATIONAL DOSE - The dose received by an individual in the course of employment in which the individual's assigned duties for the licensee or registrant involve exposure to sources of radiation. Occupational dose does not include dose received from background radiation, as a patient from medical practices, from voluntary participation in medical research programs, or as a member of the public.

PHOTON - The carrier of a quantum of electromagnetic energy. Photons have an effective momentum but no mass or electrical charge.

PICOCURIE (pCi) - One millionth of a microcurie (3.7 x 10-2 disintegrations per second or 2.22 disintegrations per minute).

POINT SOURCE - A radioactive material source which is confined to a volume whose dimensions are so small that there is no significant absorption of the emitted radiation and small compared with the distance between the source and the place at which the radiation field is to be measured. The radiation of a point source is presumed to be emitted isotropically (equally in all directions) over the full 4 solid angle.

POSITRON - Particle equal in mass to the electron and having an equal but positive charge. (See "beta particle" and "electron".)

PROTON - An elementary particle with a single positive elementary charge (1.6022 x 10-19 coulomb) and a rest mass of 1.007276470 atomic mass units (1.672486 x 10-24 gram), approximately 1836 times more than that of an electron. Protons are the constituents of all nuclei. The atomic number (Z) of an atom is equal to the number of protons in its nucleus.

QUALITY FACTOR (Q) - The linear energy transfer (LET) dependent factor by which absorbed doses are multiplied to obtain (for radiation protection purposes) a quantity that expresses, on a common scale for all ionizing radiations, the effectiveness of the absorbed dose. A legislated value of the relative biological effectiveness.

RAD - (Acronym for "radiation absorbed dose.") The basic traditional unit of absorbed dose of ionizing radiation. A dose of one rad means the absorption of 100 ergs of radiation energy per gram of absorbing material or 0.01 J/kg. One rad equals 0.01 gray.

RADIATION (1) - The emission and propagation of energy through space or through a material medium in the forms of waves; for instance, the emission and propagation of electromagnetic waves, or of sound and elastic waves.

(2) The energy propagated through space or through a material medium as waves, for example, energy in the form of electromagnetic waves or of elastic waves. The term radiation or radiant energy, when unqualified, usually refers to electromagnetic radiation. Such radiation commonly is classified, according to frequency, as Hertzian, infrared, visible (light), ultraviolet, x ray, and gamma ray. (See "photon.")

(3) By extension, corpuscular emissions, such as alpha and beta radiation, or rays of mixed or unknown type, as cosmic radiation.

RADIATION AREA - Any area, accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 0.05 mSv (0.005 rem) in 1 hour at 30 centimeters from the source of radiation or from any surface that the radiation penetrates.

RADIOACTIVE MATERIAL - Any solid, liquid or gaseous substance which emits radiation spontaneously.

RADIOACTIVITY - The spontaneous decay or disintegration of an unstable atomic nucleus, usually accompanied by the emission of ionizing radiation.

RADIOISOTOPE - An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation. The term "radionuclide" is often erroneously used as a synonym for "radioisotope" which properly has a more limited meaning. Whereas radioisotopes are the various radioactive forms of a single element with the same atomic number (and hence are a family of radionuclides), radionuclides comprise all radioisotopes of all the elements. (See "isotope," "nuclide," and "radionuclide.")

RADIONUCLIDE - Nuclides which are unstable and that decay or disintegrate spontaneously, emitting radiation. More than 1300 natural and artificial radionuclides have been identified.

RELATIVE BIOLOGICAL EFFECTIVENESS (RBE) - A factor used to compare the biological effectiveness of different types of ionizing radiation. It is the inverse ratio of the amount of absorbed radiation, required to produce a given effect, to a standard (or reference) radiation required to produce the same effect. The RBE of a specific radiation depends on the exact biological effect on a given species of organism under a given set of experimental conditions.

REM (Acronym for "roentgen equivalent man.") - The unit of dose of any ionizing radiation which produces the same biological effect as a unit of absorbed dose of ordinary x rays. The dose equivalent in rems equals the quality factor, Q, times the absorbed dose, D, in rads. One rem equals 0.01 sievert.

RESTRICTED AREA - Any area access to which is limited by the licensee or registrant for purposes of protecting individuals against undue risks from exposure to sources of radiation.

ROENTGEN (R) - A unit of exposure to ionizing radiation. It is the amount of gamma or x rays required to produce ions carrying one electrostatic unit of electrical charge (either positive or negative) in one cubic centimeter of dry air under standard conditions. One roentgen equals 2.58 x 10-4 coulomb per kilogram of air. Named after Wilhelm Roentgen, the German scientist who discovered x rays in 1895.

SEALED SOURCE - Any device containing radioactive material to be used as a source of radiation which has been constructed in such a manner as to prevent the escape of any radioactive material.

SHALLOW DOSE EQUIVALENT(H[S]) - Applies to the external exposure of the skin or an extremity, and is the dose equivalent at a tissue depth of 0.007 centimeter (7 milligrams per square centimeter) averaged over an area of 1 square centimeter.

SIEVERT (Sv) - The SI unit of dose of any ionizing radiation which produces the same biological effect as a unit of absorbed dose of ordinary x rays. The dose equivalent in sieverts equals the quality factor, Q, multiplied by the absorbed dose, D, in grays. One sievert equals 100 rem.

SPECIFIC ACTIVITY (SpA) - The radioactivity of a radioisotope of an element per unit weight of the element in a sample. The activity per unit mass of a pure radionuclide. The activity per unit weight of any sample of radioactive material.

SPECIFIC IONIZATION - The number of ion pairs formed per unit of distance along the track of an ion passing through matter.

STOCHASTIC EFFECT (probabilistic effect) - A health effect that occurs randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose without threshold.

SURVEY An evaluation of the radiological conditions and potential hazards incident to the production, use, transfer, release, disposal, or presence of sources of radiation. Such an evaluation includes, but is not limited to, measurements or calculations of levels of radiation, or concentrations or quantities of radioactive material present.

TELETHERAPY - A method of radiation therapy in which the source of radiation is at a distance of 6 centimeters or more from the area being treated.

UNRESTRICTED AREA - Any area access to which is not controlled by the licensee or registrant for purposes of protection of individuals from exposure to radiation and radioactive material, and any area used for residential quarters.

VERY HIGH RADIATION AREA - Any area, accessible to individuals, in which radiation levels could result in an individual receiving an absorbed dose in excess of 5 Gy (500 rad) in 1 hour at 1 meter from a source of radiation or from any surface that the radiation penetrates.

WEIGHTING FACTOR (w[T]) - The proportion of the risk of stochastic effects resulting from irradiation of an organ or tissue (T) to the total risk of stochastic effects when the whole body is irradiated uniformly.

X RAYS - Penetrating electromagnetic radiations whose wave lengths are shorter than those of visible light. They are usually produced by bombarding a metallic target with fast electrons in a high vacuum. In nuclear reactions, it is customary to refer to photons originating in the nucleus as gamma rays, and those originating in the extranuclear part of the atom as x rays. These rays are sometimes called roentgen rays after their discoverer, W. C. Roentgen.