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Oregon State University

Radiation Safety Glossary

absorbed dose
A measure of the energy deposited in any substance by ionizing radiation per unit mass of the substance. It is expressed numerically in rads (traditional units) or grays (International System or SI units).

activity
The rate at which an isotopes decays. Specifically, the number of disintegrations or other transforms per unit time in the radioactive material of interest.  The traditional unit for activity is the Curie, which represents 3.7 X 1010 transformations per second. The SI (International System) unit of activity is the Becquerel (Bq), which is defined as one disintegration per second.

activity, specific
The number of disintegrations or transforms per unit of time per unit amount of the material of interest. The SI unit of “activity” is becquerel, Bq, while that of "specific activity" is Bq/kg. The old unit of "activity" was the curie, Ci, while that of "specific activity" was Ci/g.

acute exposure
The absorption or ingestion of a large amount of radiation or radioactive material over a short period of time.

acute health effects
The prompt radiation effects for which the severity of the effect varies with the dose, and for which a practical threshold exists.

ALARA
The acronym for "As Low as Reasonably Achievable."  This is the basic philosophy of radiation safety.  It means making every reasonable effort to maintain exposures to ionizing radiation as far below the dose limits as practical.

alpha particle
A positively charged particle ejected spontaneously from the nuclei of some radioactive elements. Alpha particles have two protons and two neutrons bound together in a particle identical to a helium nucleus.  Alphas have a short range and low penetrating power. The most energetic alpha particle will generally fail to penetrate the dead layers of cells covering the skin and can be easily stopped by a sheet of paper. Alpha particles are hazardous when emitted by radionuclides deposited inside the body.

ancillary workers
Individuals who frequent an area where radioisotopes or radiation machines are used but do not routinely work in the area. Examples include Facilities Services, Security, and Departmental office personnel, storekeepers, etc. Ancillary workers must complete safety training provided by Radiation Safety. 

Annual Limit of Intake (ALI)
The derived limit for the permissible amount of radioactive material taken into the body of an adult radiation worker by inhalation or ingestion in a year.

atom
The smallest particle of an element that cannot be divided or broken up by chemical means.  The atomic nucleus consists of a mix of positively charged protons and electrically neutral neutrons (except for hydrogen, which has no neutrons).  Negatively charged electrons revolve in orbits in the region surrounding the nucleus. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.

atomic number
The number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table.  Carbon has 6 protons.  Thus, its atomic number is 6.  Every isotope of an element has the same atomic number.  It is represented by the symbol "Z" in atomic nomenclature. 

atomic mass
The total number of protons and neutrons in the nucleus of an atom.  The atomic mass of an element is the sum of the number of protons AND neutrons. For example, carbon has six protons. A particular isotope of carbon also has 6 neutrons. This means that its atomic mass is 12. Another isotope of carbon with 8 neutrons would have an atomic mass of 14.  It is represented by the symbol “A” in atomic nomenclature.

auger electron
The orbital electron emitted from the electron "cloud" of an atom during the process of the atom dropping from excited state to ground state.  Usually accompanied by emission of low-energy photons during realignment of the electrons in shells.

background radiation
Radiation from cosmic sources; naturally occurring radioactive materials, including radon (except as a decay product of source or special nuclear material), and global fallout as it exists in the environment from the testing of nuclear explosive devices. It does not include radiation from source, byproduct, or special nuclear materials regulated by the Nuclear Regulatory Commission. The typically quoted average individual exposure from background radiation is 360 millirems per year.

Becquerel (Bq)
The unit of radioactive decay equal to one disintegration per second. The Becquerel is the basic unit of radioactivity used in the international system of radiation units, referred to as the International System or “SI” units.
          37 billion (3.7×1010) becquerels = 1 curie (Ci).

beta particle, β
A charged particle emitted during radioactive decay, with a mass equal to 1/1837 that of a proton. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron. Beta emitters can also be harmful if they enter the body. Beta particles have greater speed and penetrating power than alpha particles but can be stopped by thin sheets of metal or plastic.

bioassay
The determination of kinds, quantities, or concentrations and, in some cases, the locations of radioactive material in the human body, whether by direct measurement (in vivo counting) or by analysis and evaluation of materials excreted or removed (in vitro) from the human body.

biological half-life, T1/2b
The time required for a biological system, such as that of a human, to eliminate, by natural processes, half of the amount of a substance (such as a radioactive material) that has entered it.

bremsstrahlung
The electromagnetic radiation produced by a change in the velocity of an electrically charged subatomic particle when it collides with another object.  It is usually associated with energetic beta emitters, such as 32P. The term is German for “braking radiation”.

calibration
The check or correction of the accuracy of a measuring instrument to assure proper operational characteristics.

committed dose equivalent
The dose equivalent to organs or tissues of reference that will be received from an intake of radioactive material by an individual during the 50-year period following intake.

committed effective dose equivalent
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 (CDE) to each of these organs or tissues. This is a measure of the overall risk associated with internal deposition of radioactive material.

controlled area
Any location, access to which is controlled for radiation safety purposes.  No minimum radiation exposure rates or amounts of radioactive materials are required in order for a location to qualify.

count
One electrical pulse caused by interaction of ionizing radiation with the detector.  Counts are related to activity by counting system efficiency factor.

Curie (Ci)
The original unit used to express the decay rate of a sample of radioactive material. The curie is equal to that quantity of radioactive material in which the number of atoms decaying per second is equal to 37 billion (3.7×1010). It was based on the rate of decay of atoms within one gram of radium. It is named for Marie and Pierre Curie who discovered radium in 1898. The curie is the basic unit of radioactivity used in the system of radiation units in the United States, referred to as "traditional" units.

decay, radioactive
The decrease in the amount of any radioactive material with the passage of time due to the spontaneous emission from the atomic nuclei of either alpha or beta particles, often accompanied by gamma radiation.

decay constant
The ratio of the amount of radioactive substance which disintegrates in a unit of time to the amount of substance present.  This is constant for any radioisotope.

decay products
Decay products are also called "daughter products". They are radionuclides that are formed by the radioactive decay of parent radionuclides. In the case of radium-226, for example, nine successive different radioactive decay products are formed in what is called a "decay chain." The chain ends with the formation of lead-206, which is a stable nuclide.

declared pregnant worker
A woman who is also a radiation worker and has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception.

decontamination
The reduction or removal of contaminating radioactive material from a structure, area, object, or person. Decontamination may be accomplished by treating the surface to remove or decrease the contamination or letting the material stand so that the radioactivity is decreased as a result of natural decay.

deep-dose equivalent
The dose equivalent at a tissue depth of 1 cm; applies to external exposure.

delayed health effects
Radiation health effects which are manifested long after the relevant exposure.  The vast majority are stochastic, that is, the severity is independent of dose and the probability is assumed to be proportional to the dose, without threshold.

deterministic effect
Health effects that can be related directly to the radiation dose received.  The severity increases as the dose increases.  A threshold is believed to exist below which the effect will not occur. Deterministic effects generally result from the receipt of a relatively high dose over a short time period. Skin erythema (reddening) and radiation-induced cataract formation are examples of deterministic effects (formerly called a nonstochastic effect).

disintegration
The transform of an atom into an atom of another species via emission of a nuclear particle.  See decay. 

dose
The measure of radiation energy present, energy absorbed, or of effect of irradiation.  See roentgen, rad, gray, rem, sievert for units of dose.

dose equivalent
The product of the absorbed dose in tissue and the quality factor (a value that reflects the biological impact of a particular type of ionizing radiation). Measured in rem or Sievert (Sv).

dosimeter
A device for measuring radiation dose.  Commonly a small device used to measure dose to an individual via photographic film or thermal luminescence.

dosimetry
The determination of radiation doses to individuals or groups.  Commonly divided into external dosimetry (doses of radiation originating outside the individual) and internal dosimetry (doses from radioactive materials inside the individual).

efficiency factor
The factor which relates observed reading to true value.  For geiger counters, LSC's etc., efficiency = cpm/dpm and is often expressed as percentage.

electromagnetic radiation
A traveling wave motion resulting from changing electric or magnetic fields.  Familiar types of electromagnetic radiation range from x rays (and gamma rays) of short wavelength, through the ultraviolet, visible, and infrared regions, to radar and radio waves of relatively long wavelength. Only the higher-energy (higher frequency/shorter wavelength) forms of electromagnetic radiation are ionizing. Radiation in the lower-energy ranges, such as visible, infrared, radar, and radio waves, are nonionizing.

electron
An elementary particle with a negative charge and a mass 1/1837 that of the proton. Electrons surround the positively charged nucleus and determine the chemical properties of the atom.

electron capture
method of radioactive decay where an orbital electron is captured by the atomic nucleus.  Electron plus one proton are converted to a neutron, changing the atom to that of another chemical species, and resulting in emission of one or more x-rays due to rearrangement of remaining orbital electrons.  Often called "k capture" since an electron from the innermost orbit (k) is most likely to be captured.

electron capture detector (ECD)
The metal "cell" containing a quantity of tritium or nickel-63.  In gas chromatography the gas flows through the ECD cell during determination of certain gasses.

electron volt
eV; kinetic energy obtained by accelerating one electron by electrical potential of one volt.  One calorie is about 2.6 x 1019 eV.  Common multiples are kilo-electron volt (KeV) and mega electron volt (MeV).

erythema
The redness of skin caused by ionizing radiation or other energy input.  Threshold radiation dose for visible erythema to human skin is 400-1000 rem, depending on skin location, characteristics of the individual, etc.

exposure
The amount of ionization in air produced by the radiation is called the exposure. Exposure is expressed in terms of a scientific unit called a Roentgen (R). The unit Roentgen is equal to the amount of radiation that produces in one cubic centimeter of dry air at 0°C and standard atmospheric pressure ionization of either sign equal to one electrostatic unit of charge.

external dose
The portion of the dose equivalent received from radiation sources outside of the body.

eye (lens) dose equivalent
The dose equivalent to the lens of the eye at a tissue depth of 0.3 cm (300 mg/cm2).

gamma ray
High-energy, short wavelength, electromagnetic radiation emitted from the nucleus. Gamma radiation frequently accompanies alpha and beta emissions and always accompanies fission. Gamma rays are very penetrating and are best stopped or shielded by dense materials, such as lead or uranium. Gamma rays are similar to X-rays.

Geiger-Mueller (GM) counter
A radiation detection and measuring instrument. It consists of a gas-filled tube containing electrodes, between which there is an electrical voltage, but no current flowing. When ionizing radiation passes through the tube, a short, intense pulse of current passes from the negative electrode to the positive electrode and is measured or counted. The number of pulses per second measures the intensity of the radiation field. It was named for Hans Geiger and W. Mueller, who invented it in the 1920's. It is sometimes called simply a Geiger counter or a G-M counter.

Gray
The international system (SI) unit of absorbed dose. One Gray (Gy) is equal to one joule of energy deposited in one kg of a material.  It is the equivalent of 100 rads (the traditional unit). 

half-life, radioactive T1/2
The time in which one-half of the activity of a particular radioactive substance is lost due to radioactive decay. Measured half-lives vary from millionths of a second to billions of years. Also called physical or radiological half-life.

half-life, biological
The time required for an organism to eliminate 50% of a material via biological mechanisms.

half-life, effective
The combined effect of physical half-life and biological half-life.

Health Physics
The science concerned with recognition, evaluation, and control of health hazards from ionizing radiation.

high radiation area
Any area accessible to individuals where radiation exists in intensities such than an individual could incur a dose of 100 millirem in one hour to a major portion of the body.

human use
The internal or external administration of radiation or radioactive materials to human beings.

internal conversion
The method of energy transfer from an excited nucleus whereby the nucleus transfers enough energy to an orbital electron so that the nucleus goes to "ground state", the electron is emitted from its orbit, and x-rays are emitted during rearrangement of remaining orbital electrons.

internal dose
That portion of the dose equivalent received from radioactive material taken into the body.

ion
An atom that has too many or too few electrons, causing it to have an electrical charge, and therefore chemically active.

ionizing radiation
Radiation capable of causing a neutral atom or a molecule to acquire positive or negative charge.  Usually results in ejection of an electron from the atom or molecule, leaving a large positive charged fragment.

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 radiations can cause ionization.

isotopes
One of two or more atoms with the same number of protons, but different numbers of neutrons in their nuclei. Thus, carbon-12, carbon-13, and carbon-14 are isotopes of the element carbon.  The numbers denote the mass number of each isotope. Isotopes have very nearly the same chemical properties, but often have different physical properties. For example, carbon-12 and carbon-13 are stable; carbon-14 is unstable, that is, it is radioactive.

LD50/60
The dose of radiation expected to cause death within 60 days to 50% of those exposed.

limits
The permissible upper bounds of radiation exposure, releases, or contamination.

Linear No Threshold (LNT) Hypothesis
Under the LNT Hypotesis, risks due to very low levels of radiation are estimated by extrapolating a line on a graph from the data existing from subjects who had much higher doses.

Liquid Scintillation Counter (LSC)
A device for measuring radioactivity, usually beta particles, emitted from a sample dispersed in a liquid scintillation cocktail. Samples are dissolved or suspended in a "cocktail" containing a solvent (historically aromatic organics such as benzene or toluene, but more recently less hazardous solvents are used), typically some form of a surfactant, and small amounts of other additives known as "fluors" or scintillators.

microcurie
One millionth (10-6) of a curie.  The symbol for the microcurie is µCi.

millicurie
One thousandth of a curie.  The symbol for millicurie is mCi.

neutron
An uncharged elementary particle with a mass slightly greater than that of the proton, and found in the nucleus of every atom heavier than hydrogen.

non-radiation workers
Personnel working in labs authorized for unsealed radioisotopes, but not personally working with radioisotopes.  Examples of non-radiation workers are lab workers, student workers, personnel from other labs who use equipment or facilities in the lab, etc.  Program Directors are responsible for identifying these individuals, providing training and documenting the training.

nonstochastic effect
Health effects, the severity of which varies with the dose and for which a threshold is believed to exist.  Radiation-induced cataract formation is an example of a nonstochastic effect (also called a deterministic effect).

nucleus
The small, central positively charged region of an atom that carries essentially all the mass. Except for the nucleus of ordinary (light) hydrogen, which has a single proton, all atomic nuclei contain both protons and neutrons. The number of protons determines the total positive charge, or atomic number. This is the same for all the atomic nuclei of a given chemical element. The total number of neutrons and protons is called the mass number.

nuclide
An atom specified by the number of protons and neutrons, such as carbon 14.

occupational dose
Occupational dose - the dose received by an individual in a restricted area or while performing assigned duties that involve exposure to sources of radiation.  Does not include doses incurred during medical diagnosis or treatment of the individual or doses of "background" radiation, e.g., cosmic radiation, radiation from rocks and dirt, radiation from naturally-occurring substances in human bodies, etc.

photon
A quantum (or packet) of energy emitted in the form of electromagnetic radiation. Gamma rays and x rays are examples of photons.

positron
A subatomic particle with the same mass as an electron and a numerically equal but positive charge.

Program Director (PD)
A faculty member or researcher who has been approved through the Radiation Safety Committee for the purchase and use of radioactive materials or radiation machines.

proton
An elementary nuclear particle located in the nucleus of an atom. The proton has a single positive electric charge.

public dose
The dose received by a member of the public from exposure to radiation or radioactive material released by a licensee or registrant, or to another source of radiation within a licensee's or registrant's control. It does not include occupational dose or doses received from background radiation, as a patient from medical practices, or from voluntary participation in medical research programs.

quality factor
A factor relating absorbed dose to effect caused to the target material.  Quality factor = rem/rad and will vary with types and energies of radiation and with nature of target materials.  Quality factor replaces Relative Biological Effectiveness for personnel dosimetry purposes.

rad
The original unit developed for expressing absorbed dose, which is the amount of energy from any type of ionizing radiation (e.g., alpha, beta, gamma, neutrons, etc.) deposited in any medium (e.g., water, tissue, air). A dose of one rad is equivalent to the absorption of 100 ergs (a small but measurable amount of energy) per gram of absorbing tissue. The rad has been replaced by the Gray in the SI system of units (1 Gray = 100 rad).

radiation
One means of propagating energy through space.  Commonly used to mean ionizing radiation as opposed to light, sound, heat, and other forms of radiation.

radiation area
Any location accessible to humans wherein an individual could incur a whole body dose of five millirem in any one hour or one hundred millirem in any five consecutive days.

Radiation Safety Committee (RSC)
The University committee, required by state law, charged with reviewing proposed possessions and uses of ionizing radiation at OSU facilities, recommending policy and overseeing the OSU radiation safety program.

Radiation Safety
The organization established by OSU Administration to provide radiation safety services, liaison with regulatory agencies, etc.

Radiation Safety Officer (RSO)

The head of Radiation Safety.

radioactivity
The disintegration of unstable atomic nuclei by emission of radiation. The process of undergoing the transformation of an unstable nucleus by the spontaneous emission of radiation, generally alpha or beta particles, often accompanied by gamma rays, from the nucleus of an unstable radionuclide. Often used also to express the rate at which radioactive material emits radiation. Measured in units of becquerels in the SI system of units or curies in the traditional system of units.

radioisotope
An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation. Approximately 5,000 natural and artificial radioisotopes have been identified.

radiosensitivity
The relative susceptibility of cells, tissues, organs, organisms, or other substances to the injurious action of radiation.

rem
A unit of effective absorbed dose equivalent of ionizing radiation in human tissue, equivalent to one Roentgen of X-rays. It is the product of absorbed dose and the Quality Factor.

Roentgen
A unit of radiation exposure equal to the quantity of ionizing radiation that will produce one electrostatic unit of electricity in one cubic centimeter of dry air at 0°C and standard atmospheric pressure.

sealed source
Any special nuclear material or byproduct encased in a capsule designed to prevent leakage or escape of the material.

shallow dose equivalent
The dose equivalent at a tissue depth of .007 cm (7 mg/cm2) averaged over 1 cm2; applies to external whole body or extremity exposure.

Sievert (Sv)
The SI (International Standard) unit for the dosage of ionizing radiation equal to 100 rems (1 Sv = 100 rems).

somatic effect
Effects of radiation limited to the exposed individual, as distinguished from genetic effects which may affect subsequent unexposed generations.

source material
uranium or thorium or any combination thereof in any physical or chemical forms, or ores containing 0.05% or greater of uranium or thorium or any combination thereof.  However, source material does not include special nuclear materials or progeny of uranium or thorium.

special nuclear material
Plutonium, uranium-233, uranium-235, uranium enriched in 233U and/or 235U, and any other material designated by the regulatory agencies, but not including source material.

stochastic effects
Effects that occur by chance and which may occur without a threshold level of dose, whose probability is proportional to the dose and whose severity is independent of the dose. In the context of radiation protection, the main stochastic effect is cancer.

survey meter
Any portable radiation detection instrument especially adapted for inspecting an area or individual to establish the existence and amount of radioactive material present.

teratogenic effects
Birth defects that are not passed on to subsequent generations, caused by exposure of a fetus.

thermoluminescent dosimetry
A small device used to measure the radiation dose by measuring the amount of light emitted from a crystal in the detector when the crystal is heated after being exposed to the radiation.

Total Effective Dose Equivalent TEDE
The sum of the deep-dose equivalent (DDE) for external exposures and the committed effective dose equivalent (CEDE) for internal exposures.

Total Organ Dose Equivalent, Maximum Organ (TODE)
The sum of the deep dose equivalent (DDE) and the committed dose equivalent (CDE) to the organ receiving the highest dose.

transform
A change of an atom from one energy state to another or from one chemical species to another.

tritium
A radioactive isotope of hydrogen. Tritium contains one proton and two neutrons in its nucleus. Because it is chemically identical to the natural hydrogen atoms present in water, tritium can easily be taken into the body by ingestion. It decays by beta emission and has a radioactive half-life of about 12.5 years.

unrestricted area
An area, access to which is neither limited nor controlled by the licensee or registrant.

unsealed sources
Unsealed radioactive material (also called isotopes) refers to radioactive chemicals used in laboratory research for their tagging, labeling, tracing, radiation, or decay properties. In a laboratory setting, these isotopes are usually used in very small quantities, which limit the possible extent of any radiological accident. Unsealed radioactive material is also variously referred to as (radio-) isotopes, (radio-) nuclides, byproduct material, licensed material, or activated material.

Weighting factor (WT)
For an organ or tissue, (T) is the proportion of the risk of stochastic effects resulting from irradiation of that organ or tissue to the total risk of stochastic effects when the whole body is irradiated uniformly.

whole body
For purposes of external exposure, whole body means the head, trunk (including male gonads), arms above the elbow, and legs above the knee

X-ray
Penetrating electromagnetic radiation (photon) having a wavelength that is much shorter than that of visible light. These rays are usually produced by excitation of the electron field around certain nuclei. In nuclear reactions, it is customary to refer to photons originating in the nucleus as gamma rays, and to those originating in the electron field of the atom as X-rays.