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Information Directory

Reference Directory


Absorbed Dose – See “Dose”

Acoustic Energy – Mechanical energy transported by an acoustic wave. The units are those of acoustic power times time.

Acoustic Impedance – A vector quantity formed by taking the ratio of the instantaneous acoustic pressure at the surface to the instantaneous volume velocity at the surface in an acoustic field.

Acoustic Impedance Mismatch – A condition of unequal characteristic acoustic impedances of contiguous media, causing reflection of acoustic energy at the interface.

Acoustics – The science of sound, including its production, transmission and effects.

Activation – The process of making a material radioactive by bombardment with neutrons, protons, or other nuclear radiation.

Activity – A radiation quantity describing the number of atoms decaying in a given amount of radioactive material per unit time (also referred to as the rate of decay). The unit of measure is the curie (Ci) or the becquerel (Bq).

Acute Exposure – A large exposure (typically greater than 10 rads) received over a short period of time (acutely).

Acute Radiation Syndrome – See “Syndrome”

Agreement State – Any state in the United States where the USNRC has agreed that the state can perform the USNRC regulatory functions relative to the licensing and control of radioactive material used or produced within that state.

Airborne Contamination – The term applied to radioactive contamination loose in the air, filtered (trapped) from the air, or deposited from the air, as contrasted with contamination spread by splashing, dripping, etc.

ALARA – An acronym standing for “as low as is reasonably achievable”. The term refers to an operating philosophy in which occupational exposures are reduced as far below specified limits as can be justified, with societal and economic factors taken into account.

Alpha Particle – A positively charged (+2) particle emitted from the nucleus of an atom. It is identical to a helium nucleus, that is, it has two protons and two neutrons (but no atomic electrons).

Ancillary – Supplementary.

Annihilation – A process converting mass into energy whereby a positron (positive beta particle) and an electron (negative beta particle) interact, causing the particles to disappear and their masses to convert into energy (two 0.511million electron volt (MeV) photons).

Anode – One of two electrodes present in radiation instrumentation that is positively charged with respect to the cathode, and is therefore used to collect negatively charged electrons produced through the ionization process.

Appraisal – A comprehensive evaluation of the overall adequacy and effectiveness of a radiation protection program.

Atom – The smallest unit of an element.

Atomic Number – The number of protons in the nucleus of an atom. The atomic number is also called the Z-number.

Background Radiation – The radiation in the natural environment, including cosmic rays and radiation from the naturally occurring radioactive elements, both outside and inside the bodies of humans and animals.

Backscatter – A charged particle interaction undergone by beta particles whereby the beta impacts on a surface and is scattered backwards through an angle greater than 90 degrees. Backscatter increases with increasing energy of the beta particle and atomic number of the surface medium.

Beta Particle – A charged particle emitted from a nucleus during radioactive decay. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron.

Becquerel – The basic unit of radioactivity in the International System of Units (SI System). The becquerel, abbreviated Bq, is equivalent to one radioactive atom disintegrating in one second (one disintegration per second). There are 37 billion Bq in one curie of radioactivity.

Bioassay – The collection and analysis of human tissue or byproducts (hair, tissue, nasal smears, urine or fecal samples) to determine the amount of radioactive material that might have been ingested by the body, or, alternatively, the direct assessment of radioactivity in the body utilizing external measurements.

Black Body – An ideal body that is in thermal equilibrium with the electromagnetic energy incident upon it. It behaves as if the incident energy is completely absorbed. The electromagnetic energy radiated by such a body in each spectral region is the maximum obtainable from any body at the same temperature.

Breathing Zone Samplers – Air sampling devices designed to be positioned close to an occupational worker’s face in order to collect a sample representative of the air the worker is breathing.

Bremsstrahlung – The emission of photon radiation occurring when charged particles (principally beta and high energy electron radiations) interact with other atoms. Bremsstrahlung is also known as “braking radiation”.

Byproduct Material – A term referring to material that becomes radioactive through the process of producing special nuclear material.

Calibration – The determination of a measuring instrument’s ability to respond accurately to a source of radiation or radioactive contamination.

Cathode – One of two electrodes in a radiation detection device, negatively charged with respect to the anode, which collects positively charged ions produced through the ionization process.

Cathode Ray Tube (CRT) – An electron beam tube designed for two-dimensional display of signals as a function of their coordinates in space, time or both. It typically consists of an electron source (gun), a means of deflecting the electronic beam in the “x” and “y” directions, and a phosphorous screen upon which the position of the electron beam is visible.

Cavitation (Acoustically-induced) – A phenomenon produced by sound in liquid or liquid-like media involving bubbles or cavities containing gas or vapor.

Certified Health Physicist – An individual who has been Certified in the practice of health physics by the American Board of Health Physics. A Certified Health Physicists may be referred to as a “CHP”, or as a “Diplomat of the American Board of Health Physics”.  CHPs are typically members in good standing of the American Academy of Health Physics.

CHP – See “Certified Health Physicist”

Chronic Exposure – Small radiation exposures received over a long period of time.

Compton Effect – One of three principal photon interactions with matter in which the photon imparts some of its energy to an electron orbiting the nucleus. The electron is subsequently ejected from the atom along with the photon.

Controlled Area – An area that a licensee establishes to limit access to radiation sources.

Contamination – The deposition of unwanted radioactive material in any place where it is not desired (e.g., on the surfaces of structures, areas, objects, or personnel).

Contamination Control – The process of minimizing the creation and spread of contamination.

Contamination Survey – A survey, often performed utilizing portable instrumentation, to detect the presence of radioactive material.

Cosmic Radiation – Penetrating ionizing radiation, composed primarily of charged particles of very high energies, originating in space.

Cosmogenic Radionuclides – Radionuclides produced by the interaction of cosmic radiations with the earth’s atmosphere. Carbon-14 and Hydrogen-3 (tritium) are two well-known examples.

Count – The response of a device designed to detect ionizing radiation events. It may refer to a single detected event or to the total number of events registered in a given period of time. The term is often used erroneously to designate a disintegration, ionizing event, or voltage pulse.

Cross-contamination – Contamination not from an original source, but acquired from another contaminated object.

Curie – The conventional unit of radioactivity. The curie, abbreviated Ci, is equal to 37 billion nuclear disintegrations per second.

CW Laser – Continuous-wave laser, as distinguished from a pulsed laser. A laser emitting for a period in excess of 0.25 second.

Daughter – Synonym for decay product or progeny.

Decay, Radioactive – The disintegration of the nucleus of an unstable nuclide by the spontaneous emission of charged particles and/or photons.

Decay Series – The sequence of radioactive decays, each creating a new radioactive element, that the original radioactive element (the series parent) must undergo to achieve stability.

Decibel – A unit used for expressing the ratio of two like quantities, such as electrical signal amplitudes or sound energies.

Decontamination – The reduction or removal of radioactive contamination from a given surface.

Delayed Effect – An effect arbitrarily defined as occurring more than two months (often years) following an acute or chronic exposure. Delayed effects include solid cancers, leukemia, and genetic effects.

Detector, Radiation – Any device for converting radiant energy to a form more suitable for observation. An instrument used to determine the presence, and sometimes the amount, of radiation.

Doppler Effect – A shift in observed frequency (and wave length) caused by relative motions among sources, receivers, and the propagation medium when there is a component of relative motion parallel to the beam axis.

Dose – The radiation quantity describing the amount of ionizing radiation (or energy) deposited in a given mass of material. The term dose is also referred to as the “absorbed dose”. Dose has units of rads or grays.

Dose Equivalent – The product of the dose (in rads or grays) and the quality factor. The dose equivalent is the quantity which utilizes the quality factor to account for the biological effectiveness of the different radiation(s) under consideration. The dose equivalent has units of rems or sieverts.

Dose Rate – The radiation dose delivered per unit of time.

Dosimeter – A device placed in an area or on a person for the purpose of measuring and registering the total accumulated exposure to ionizing radiation.

Dosimetry – The theory and application of the principles and techniques involved in the measurement and recording of radiation doses.

Electric Dipole – A pair of equal and opposite charges separated by an infinitesimal distance. When the charges are oscillating, the dipole becomes an elementary radiating electric dipole.

Electromagnetic Radiation – The propagation of varying electric and magnetic fields through space at the velocity of light.

Electron – An elementary particle with a unit negative charge. Electrons surround the positively charged nucleus and determine the chemical properties of the atom.

Electron Volt – A unit of energy.

Element – A substance that cannot be changed into simpler substances through chemical reactions.

Energy – The ability to do work. This term is often further classified into potential and kinetic energy. The conventional unit of energy is the electron volt (eV).

Energy Dependence – The characteristic response of a radiation detector to a given range of radiation energies or wavelengths, compared with the response of a standard detector.

Excitation – One of two principal interactions of charged particles with matter in which atomic electrons are raised (“excited”) to higher energy states without being ejected from the atom (see also Ionization).

Exposure – The radiation quantity used to measure the number of ionizations produced in air by photon radiations. The conventional unit of exposure is the roentgen, abbreviated R.

Exposure Rate – The exposure divided by the time over which it was accumulated.

External Radiation – Radiation from a source outside the body.

Fetal Effect – An effect occurring in the unborn embryo or fetus following an absorbed dose of radiation.

Fission – The splitting of a nucleus into at least two other nuclei and the release of a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation.

Frisk – See “Personnel Frisk”.

Gamma Ray – High-energy, short wavelength electromagnetic radiation emitted from the nucleus. Gamma rays are a type of photon radiation.

Gas-filled Detector – A detector employing a gas-filled medium for the detection of ionizing radiation. Examples include Geiger-Mueller detectors, proportional counters, and ionization chambers.

Gas Laser – A type of laser in which the laser action takes place in a gas medium. Ga lasers are usually operated as CW lasers.

Geiger-Mueller Counter – One of the three primary types of gas-filled detectors. Also called a geiger counter, this instrument is a highly sensitive, radiation measuring device, often used for contamination surveys and counting radioactive samples.

Genetic Effect – An effect occurring in the offspring of the exposed individual. Genetic effects have, to date, not been observed in human populations.

Gray – A unit, in the International System of Units (SI), of radiation dose. The gray, abbreviated Gy, is equivalent to an absorbed dose of 100 rads.

Gray Scale – A term describing the property of a display in which intensity information is recorded as variations in the brightness.

Half-life – The time in which half the atoms of a particular radioactive substance disintegrate to another radioactive or stable form.

Health Physics – A science and profession devoted to protecting people and the environment against unnecessary radiation exposure.

Hertz (Hz) – A unit of frequency (i.e., cycles per second).

Infrared Radiation – electromagnetic radiation with wavelengths which lie in the range of 0.7 to 1000 micrometers

Ingestion – The entry of radioactivity into the body through the mouth.

Inhalation – The entry of radioactivity into the body through the breathing of airborne radioactive material.

Internal Radiation – Radiation from a source within the body (as a result of the deposition of radionuclides in body tissues).

Intrabeam Viewing – Viewing a laser source from within the beam. The beam may either be direct or specularly reflected.

Inverse Square Law – A fundamental radiation protection principal applicable to certain sources of radiation in which reductions in the exposure rate vary with the square of the distance from the source.

Ion – An atomic particle or atom having either a negative or positive electrical charge.

Ion Pair – Two particles of opposite charge, usually referring to an electron and the positive atomic residue, resulting from the interaction of ionizing radiation with orbital atomic electrons.

Ionization – The removal of one or more orbital electrons from an atom.

Ionization Chamber – One of the three primary types of gas-filled detectors. Ionization chambers are designed to give a true measure of the charge produced in air and are therefore conventionally used to measure the exposure rate from gamma and x-ray radiation.

Ionizing Radiation – Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions.

Irradiance (E) – The power per unit area on a given surface, in units of watts per square centimeter

Isotope – Elements with the same atomic number, or Z-number, but a different number of neutrons in the nucleus.

Isotropic – Having the same properties in all directions.

Kinetic Energy – The energy associated with an object in motion.

Lambda – The decay constant of the radionuclide, calculated by dividing the natural logarithm of two by the half-life of the radionuclide. Lambda has units of reciprocal (one over) time.

Laser – A source of intense, coherent, directional beam of optical radiation. It is also an acronym for “light amplification by stimulated emission of radiation”. A laser is usually composed of an energy source, a resonant cavity and an active lasing medium.

Laser System – An assembly of electrical, mechanical, and optical components that includes a laser.

Latent Period – A period following an initial acute exposure where no delayed effects become apparent.

License (specific) – A document issued by a regulatory agency that gives the bearer the right to procure, receive, store, transfer, use, export, and import specified radioactive items under specific terms.

License-exempt Material – Radioactive material or items not subject to regulations, or exempt from licensing under applicable regulations.

Licensed Material – Radioactive material received, stored, possessed, used, transported or transferred under a general or specific license issued by the USNRC or an Agreement State.

Linear, No-threshold Hypothesis – The conservative assumption used in the radiation protection field that any dose of radiation, no matter how small, has a corresponding effect, that is, each increment of radiation is assumed to increase the probability of harm (also known as risk).

Magnetic Dipole – A current flowing in an infinitesimally small loop. When the current is oscillating, the dipole becomes an elementary radiating magnetic dipole.

Mass Number – The number of protons and neutrons in the nucleus. The mass number is also called the A-number.

MeV – A unit of energy equivalent to one million electron volts.

Micro- – A prefix that divides a basic unit by one million.

Milli- – A prefix that divides a basic unit by 1000.

Nano- – A prefix that divides a basic unit by one billion.

Natural Background Radiation – See “Background Radiation”.

Naturally-occurring Radioactive Material – Material which is radioactive in its natural physical state (i.e., not man- made) but does not include by-product, source, or special nuclear material.

Neutron – An uncharged elementary particle found in the nucleus of atoms.

Neutron Number – The number of neutrons in the nucleus of an atom. Also called the N-number.

Non-ionizing Radiation – Radiations that are capable of exciting electrons in atoms or molecules, but that are unable to displace them or produce ion pairs..

Non-penetrating Radiation – Radiation for which only an insignificant amount of energy is absorbed outside a source volume (for example, a human being).

Non-series Radionuclides – Radionuclides that decay in one step to a stable (non-radioactive) decay product.

Non-stochastic Effects – Effects whose severity increases with dose. A threshold dose for these effects is assumed. Examples include erythema (reddening of the skin) and cataract (opacity in the lens of the eye) formation.

NORM – An acronym standing for “naturally-occurring radioactive material”.

Nucleons – A term referring to the particles (protons and neutrons) residing in the nucleus.

Nucleus – The small, central, positively charged region of an atom that carries essentially all the atom’s mass.

Nuclide – An atom containing a particular number of protons and neutrons.

Optically Pumped Lasers – A type of laser that derives energy from another optical radiation source such as a xenon flash lamp.

Pair Production – One of three principal interactions of photons with matter in which complete absorption of the incident photon energy occurs with the simultaneous production of an electron-position pair. This interaction can only occur for gamma-ray exceeding a certain (threshold) energy.

Parent – A radionuclide which, upon disintegration, yields a specified nuclide, either directly or as a later member of a radioactive series.

Penetrating Radiation – Radiations for which a significant amount of energy is absorbed outside a source volume (for example, a human being).

Personnel Frisk – The process of slowly passing a radiation detector over the whole body (or a portion of the body) to detect the presence of radioactive contamination.

Photoelectric Effect – One of three principal photon interactions with matter where the photon essentially disappears following an interaction with an electron orbiting the nucleus. The electron absorbs the photon’s energy and is ejected from the atom.

Photon – A packet of energy emitted in the form of electromagnetic radiation. Gamma rays and x-rays are examples of photons.

Pico – A prefix that divides a basic unit by one trillion.

Piezoelectric Effect – The property, exhibited by all electrically asymmetrical crystals, of generating electrical potentials when mechanically stressed. Conversely, these crystals generate mechanical strains when electrically stressed. This effect is the basis of electro mechanical transduction of energy in transducers

Pocket Ionization Chamber – A device that records the radiation exposure to an individual. “Direct reading” pocket chambers can be read directly by the individual at any time for an estimation of the dose received.

Potential Energy – The energy associated with a stationary object.

Primordial Radionuclides – Naturally-occurring radionuclides with very long half-lives that can contribute a radiation dose to humans through their presence in the air, water, and soil, etc.

Prompt Radiation Exposure – See “Acute Exposure”.

Proportional Counter – One of the three primary categories of gas-filled detectors. A proportional counter is a fairly sensitive radiation measuring device, often used for contamination surveys and counting radioactive samples.

Protective Clothing – Clothing worn by the individual to minimize the likelihood of contaminating body surfaces.

Proton – An elementary nuclear particle with a positive electric charge located in the nucleus of an atom.

Pulsed Laser – A laser that delivers its energy in short pulses, as distinct from a CW laser. In general, a pulsed laser emits for less than 0.25 seconds.

Quality Factor – The factor designed to account for the relative effectiveness that different radiations have for causing damage to biological tissue. The absorbed dose (in rads or grays) multiplied by the quality factor determines the dose equivalent (in rems or sieverts).

Quantity – A term describing a physical concept or principle. For example, volume is a quantity.

Q-Switched Laser – A laser capable of extremely high peak powers for very short durations.

Rad – An acronym standing for “radiation absorbed dose”. The rad is the basic unit of absorbed dose. A corresponding unit in the International System of Units (SI system) is the gray, equivalent to 100 rads.

Radiation – Particles or photons emitted from the nucleus of a radioactive atom as a result of radioactive decay.

Radiation-producing Machine – A machine that generates radiation without the presence of radioactive material. Examples are medical x-ray machines and linear accelerators.

Radiation Safety Procedures – Documents, typically administered by the Radiation Safety Officer (RSO), which describe how radiation protection policies should (or will) be implemented.

Radiation Worker – A person who may receive routine radiation exposure in the course of performing his or her duties for their employer.

Radioactive Decay – See “Decay, Radioactive”.

Radioactive Material – Any material or combination of materials that spontaneously gives off ionizing radiation. This includes natural elements such as radium, and artificially-produced (for example, accelerator-produced) radionuclides.

Radioactive Waste – Solid, liquid and gaseous materials from nuclear operations that are radioactive or become radioactive and for which there is no further use.

Radioactivity – The phenomenon whereby unstable atoms release energy in the form of particles and/or electromagnetic radiation by the process of radioactive decay.

Radioisotope – An isotope of an element that is unstable and decays or disintegrates spontaneously, emitting radiation.

Radionuclide – A nuclide containing an unstable number of protons and neutrons in the nucleus. The term radionuclide is related to the term radioisotope.

Release Limits – A limit on the amount of radioactive contamination that may be present on people or equipment leaving specified areas (for example, a controlled area or a restricted area).

Rem – An acronym standing for “roentgen equivalent man”. The rem, a unit of dose equivalent, is determined by multiplying the absorbed dose of any ionizing radiation by a corresponding factor that takes into account the biological effectiveness of that radiation.

Respiratory Protection – Devices designed to prevent the wearer from inhaling airborne radioactivity. Respirators should be considered when either ALARA or engineering controls are insufficient to adequately protect the worker.

Restricted Area – An area that a licensee establishes to limit radiation exposure of personnel.

Roentgen (R) – A unit of exposure to ionizing radiation which measures the amount of charge (ionizations) produced in a given mass of air. One R is equivalent to 0.879 rads in air.

Scientific Notation – A system for dealing with very large and very small numbers which corresponds to the number of times the number must be multiplied or divided by ten. For example the number 1,000,000,000 would be written as 1 x 109 and the number 0.000000001 would be written as 1 x 10-9.

Scintillation Detectors – A class of detectors that respond to ionizing radiation by emitting light flashes which are proportional to the amount of energy deposited. Examples include zinc sulfide and sodium iodide detectors.

Semiconductor Detectors – A class of solid-filled (solid-state) detectors. Examples include silicon and germanium.

Series Radionuclides – Radionuclides beginning with a long-lived isotope of uranium or thorium that decay through a chain (series) of radionuclides before reaching a stable form of lead.

Sievert – A unit, in the International System of Units (SI), of dose equivalent. The sievert, abbreviated Sv, is equivalent to 100 rems.

Solid-filled Detectors – A detector employing a solid-filled medium for the detection of ionizing radiation. Examples include scintillation and solid-state (semiconductor) detectors.

Somatic Effect – An effect that occurs in the exposed individual, as opposed to an effect that occurs in the individual’s offspring. Cancer is an example of a somatic effect.

Source Material – Radioactive material limited to uranium and thorium compounds that may require a license by the USNRC based on meeting certain regulatory conditions.

Special Nuclear Material – Radioactive materials, such as plutonium and certain uranium isotopes, designated as special nuclear material by the USNRC. Special nuclear material is able to undergo nuclear fission. Special nuclear material does not include source material.

Specific Activity – The total activity of a given nuclide per mass of the material. Typical units for specific activity are curies per gram (Ci/g) or becquerels per kilogram (Bq/kg).

Spectroscopy – The identification of a radionuclide(s) by relating the amount of energy deposited in the detector to characteristic energies emitted by the radionuclide(s).

Specular Reflection – A mirror-like reflection.

Stability – The achievement of a stable combination of protons and neutrons (nucleons) in the nucleus.

Stable – An atom containing a particular combination of nucleons resulting in no tendency to exhibit radioactivity or undergo radioactive decay.

Stochastic Effect – An effect whose probability of occurrence increases with dose. Regulations assume that no threshold exists for this effect. Cancer is an example of a stochastic effect.

Survey (radiation) – An evaluation of the radiation environment associated with the production, use or existence of radioactive materials or other sources of radiation under specific conditions. Radiation surveys often employ the use of portable (hand-held) radiation instrumentation.

Syndrome – A combination of clinical signs and symptoms occurring together so as to constitute a single clinical picture.

10 CFR 19 – The USNRC regulation entitled “Notices, Instructions and Reports to Workers – Inspection and Investigations” which establishes requirements by licensees to individuals participating in licensed activities and options regarding NRC inspections.

10 CFR 20 – The USNRC regulation establishing standards for protection against ionizing radiation resulting from activities licensed by the NRC.

10 CFR 30 – The USNRC regulation establishing general licenses for the possession, use, and ownership of byproduct material.

10 CFR 40 – The USNRC regulation establishing general licenses for the possession, use, and ownership of source material.

10 CFR 70 – The USNRC regulation establishing general licenses for the possession, use, and ownership of special nuclear material.

Terrestrial Radiation – The portion of background radiation that is emitted by naturally occurring radioactive materials in the earth.

TLD – Acronym for “thermoluminescent dosimeter”. A TLD is a detector that utilizes a light-producing material (phosphor) sensitive to ionizing radiation to measure total absorbed dose over a period of time.

Transducer – A device capable of converting energy fro one form to another.

Transmission Line – A physical structure for guiding electromagnetic energy. Common examples are wire pairs, coaxial lines, strip lines, and wave guides.

Ultrasound – Acoustic radiation at frequencies above the range of human hearing (i.e., above 20 kilohertz).

Ultraviolet Radiation – electromagnetic radiation with wavelengths between soft x-rays and visible violet light.

Unit – A specific quantity used as a standard of measure. For example, volume represents a quantity whereas liters represents a measure of that quantity.

USDOT – An acronym standing for the “United States Department of Transportation”, the federal regulatory agency principally responsible for the shipping of radioactive materials. USDOT regulations can be found in Title 49 of the Code of Federal Regulations.

USNRC – An acronym standing for the “United States Nuclear Regulatory Commission,” a federal regulatory agency which oversees various aspects associated with the receipt, storage, possession, use, transport or transfer of radioactive materials. USNRC regulations can be found in Title 10 of the Code of Federal Regulations.

Visible Radiation (light) – Electromagnetic radiation which can be seen by the human eye. It is commonly used to describe wavelengths which lie in the range of 400 and 780 nanometers.

Waste Management – The planned management of radioactive waste with the goal of minimizing the amount generated as a result of facility operations.

Whole-body Counter – A device used to identify and measure the radiation in the body of humans and animals.

X-rays – Penetrating electromagnetic (photon) radiation having a wavelength shorter than that of visible light. X-rays are produced when orbital electrons change states and release energy.