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Absorbed Dose

See Dose, Absorbed.


The phenomenon by which radiation imparts some or all of its energy to any materials through which it passes.

Action Level

The level of radioactive contamination or biologic uptake at which additional measures or cleaning must be performed. The action level varies depending upon the type of survey performed.


The number of nuclear disintegrations occurring in a given quantity of material per unit of time. See Curie and Becquerel.

Airborne contamination

Radioactive material found in sufficient quantities in the air to require that actions be taken to reduce the potential of receiving an internal dose.

Alpha Particle

A strongly ionizing particle emitted from the nucleus during radioactive decay having a mass and charge equal in magnitude to a helium nucleus, consisting of two protons and two neutrons with a double-positive charge.

Annual Limit on Intake (ALI)

ALI is the activity of a radionuclide that if taken alone would result in a person (represented by Reference Man) receiving an occupational dose limit set by the Washington State Department of Health. ALI for each nuclide is available in the State Radiation Control Regulations (WAC 246-221-290) or the NRC regulations (10CFR20 Appendix B).

As Low As Reasonably Achievable (ALARA)

A principle of radiation protection limiting radiation exposures to a level deemed as low as reasonably achievable, taking into account benefit, economic factors, and social factors.

Authorized User

See Principal Investigator (PI).


Beam Collimation

Diameter of the laser beam at which power per unit area of the beam is 1/e times that of the peak power per unit area.

Becquerel (Bq)

The International System of Units' unit for measuring the quantity of any radioactive material. One Becquerel is the quantity of radioactive material for which the number of disintegrations is one per second. See Activity and Curie.

  • One Bq = One disintegration per second
  • One mCi = 37 million Bq = 37 MBq
  • One KiloBecquerel (kBq) equals 1000 Becquerels
  • One MegaBecquerel (MBq) equals one million Becquerels
  • One GigaBecquerel (GBq) equals one billion Becquerels

Beta Particles

A charged particle emitted from the nucleus of an atom, having a mass and charge equal in magnitude to that of the electron, although the charge can be either negative or positive.


The determination of the kind, quantity or concentration, and location of radioactive materials in the human body by direct (in vivo) measurement (as in thyroid bioassay), or by analysis in vitro of materials excreted or removed from the body (as in urinalysis).



Determination of the variation from standard (or accuracy) of a measuring instrument to ascertain necessary correction factors.

Ceiling Value

Some nonionizing radiations produce physiological responses from short intense exposure; the PELs for these radiations are more appropriately based on this particular hazard. Nonionizing radiations with this type of hazard are best controlled by a ceiling value that is a maximum level of exposure, which must not be exceeded.

Contamination, Radioactive

Radioactive material in an undesired location is referred to as contamination.

Controlled Area

An area in which the occupancy and activity of those within it are subject to control and supervision for the purpose of protection from hazards.

Count (Radiation Measurements)

The indication of a device detecting ionizing radiation events. It may refer to a single detected event or to the total registered in a given period of time, or be expressed as a count rate (e.g., counts per minute (cpm) or counts per second (cps)).

Critical Organ

The organ or tissue that is at highest risk for a given isotope or radiation. For iodine, the critical organ is the thyroid gland.

Curie (Ci)

The traditional unit for measuring the quantity of any radioactive material. A curie is the quantity of any radioactive material in which the number of disintegrations is 37 x 109 per second. See Activity and Becquerel.


Decay, Radioactive

Disintegration of the nucleus of an unstable nuclide by the spontaneous emission of charged particles and/or photons.

Detector, Radiation

Any device for measuring the radiation or contamination present in an area or volume. See Geiger-Mueller Counter, Ionization Chamber, Dosimeters, and Scintillation Counter.


A spontaneous nuclear transformation (radioactivity) characterized by the emission of energy and/or mass from the nucleus. In one microcurie, there are 2,220,000 disintegrations emitted every minute.

Dose Equivalent, Effective (EDE)

The sum of the products of the dose equivalent to each organ or tissue and the weighting factor applicable to each of the body organs or tissues that are irradiated. The weighting factor is based on the relative risk of cancer from radiation exposure to the organ or tissue concerned. The traditional unit of effective dose equivalent is the rem. The SI unit is the sievert (Sv). The ICRP has recommended a new unit, the Effective Dose (ED), that will replace EDE.

Dose Equivalent (DE)

A quantity used in radiation protection expressing all radiation on a common scale for calculating the effective absorbed dose to a person. The traditional unit of dose equivalent is the rem, which is numerically equal to the absorbed dose in rads multiplied by certain modifying factors such as the quality factor. See Rem.

Dose, Absorbed

The energy imparted to matter by ionizing radiation per unit mass. The unit of absorbed dose is the rad (100 ergs/g). See Rad.


A general term denoting the quantity of radiation or energy absorbed in a specified mass. For special purposes, it must be appropriately quantified. See Dose, Absorbed; Dose Equivalent; Dose Equivalent (Effective); and Exposure.


A device to measure radiation dose. Commonly called a radiation badge or film badge. Fred Hutch uses Optically Stimulated Luminescence (OSL) or Thermal Luminescence (TL) Dosimeters for dose of record measurements.


Efficiency (Counters)

A measure of the probability that a count will be recorded when radiation is incident on a detector. Usage varies considerably, so it is best to make sure which factors (such as window transmission, sensitive volume, energy dependence, total efficiency, etc.) are specified in a given case.

Electron Capture

A mode of radioactive decay involving the capture of an orbital electron by its nucleus. X-rays are emitted as a consequence of the rearrangement of the orbital electrons.

Electron Volt (eV)

A unit of energy equivalent to the amount of kinetic energy gained by an electron in passing through a potential difference of one volt. Frequently used terms that describe larger multiple units of the electron volt are "keV" for thousands of electron volts and "MeV" for millions of electron volts. The kinetic energy of a gas molecule in air is a few hundredths of an eV. Chemical reactions are about 10 eV. Nuclear changes resulting in emissions of radiation involve thousands (keV) or millions (MeV) of electron volts.


Negatively charged elementary particle that is a constituent of every atom. Its unit of negative charge is equal to 1.6 x 10-19 coulombs. Its mass is 0.00549 atomic mass units.

Enclosed Laser System

Any laser or laser system located within an enclosure that does not permit hazardous optical radiation emission from the enclosure.


Redness of the skin caused by distention of the capillaries with blood.


A measure of the ionization produced in air by x- or gamma radiation. It is the sum of the electrical charges on all ions of one polarity (positive or negative) produced in 1 cc of air when all electrons liberated by photons are completely stopped, divided by the mass of 1 cc of air. It is equivalent to about 87.6 ergs per gram of dry air. The special unit of exposure is the roentgen (R), usually expressed as R per hour (R/hr). Exposure is not a measure of dose, but rather a measure of ionizations caused in air.


Film Badge

A packet of photographic film used for the approximate measurement of radiation exposure for staff monitoring purposes. The dosimeters at Fred Hutch no longer use film. See Dosimeter.

Fixed Contamination

Contamination that is not easily removed. Allowing time for decay can reduce fixed contamination. Fixed contamination is an exposure hazard at high levels.


Gamma Ray

Penetrating electromagnetic radiation of nuclear origin. Except for origin, identical to x-ray. Gamma rays originate from the nucleus, x-rays originate from electron energy changes.

Geiger-Mueller (GM) Counter

Highly sensitive gas-filled detector and associated circuitry used for radiation detection and measurement. The radiation ionizes the gas, and an electrode collects the ions. It does not distinguish between types of radiation (i.e., is not energy dependent) but shows the relative amount of radiation present.

Gray (Gy)

The International System of Units' unit of absorbed dose, which is equal to 1 joule per kilogram. 1 Gray = 100 rads. See Dose, Absorbed.


Half Value Layer (HVL)

The thickness of any specified material necessary to reduce the intensity of an x-ray or gamma ray beam to one-half of its original value. It is good practice to use 10 half value layers when shielding radioactive material.

Half-Life, Biological

The time required for the body to eliminate one-half of an administered dose of any substance by the biological processes of elimination. This time is approximately the same for both stable radionuclides and radionuclides of a particular element.

Half-Life, Effective

The time required for a radioactive nuclide in a system to be diminished 50 percent as a result of the combined action of radioactive decay and biological elimination.

Equation for Effective Half-Life

Half-Life, Radioactive

The time required for a radioactive substance to lose 50 percent of its activity by decay. Each radionuclide has a unique half-life.

Health Physics

The branch of radiological science dealing with the protection of staff and the environment from harmful effects of ionizing radiation.


Infrared Radiation (IR)

Invisible electromagnetic radiation with wavelengths which lie within the range of 0.70 to 1000 micrometers.

Internal Contamination

Radioactive material internally deposited in the human body.

International System of Units

The English name for the Systems International d'Unites, sometimes referred to as SI, which is a complete metric system of measurement for scientists.

Inventory Limit

The maximum activity of a radionuclide that a Fred Hutch PI can have on hand at any one time. If the inventory limit is exceeded, the PI will be prevented from receiving further radioactive material until the inventory limit has been increased by amendment or until some radioactive material is disposed. See Section 3.4, Radioactive Material Inventory Limit, for further explanation.

Inverse Square Law

The intensity of radiation at any distance from a point source varies inversely as the square of that distance. Example: if the radiation exposure is 100 R/hr at 1 inch from a source, the exposure will be 0.01 R/hr at 100 inches (100 R/hr x 12/1002 = 0.01 R/hr).


Atomic particle, atom, or chemical radical with an electrical charge, either negative or positive.

Ionization Chamber

An instrument designed to measure the quantity of ionizing radiation in terms of the charge of electricity associated with ions produced within a defined volume of air. Usually calibrated to read out in R/hr.


The process by which a neutral atom or molecule acquires either a positive or a negative charge.


The optical power per unit area reaching a surface (W/cm2).


Exposure to radiation.


Nuclides having the same number of protons in their nuclei, and hence having the same atomic number, but differing in the number of neutrons, and therefore in the mass number. Almost identical chemical properties exist between isotopes of a particular element.



Unit of energy, defined as 1.0 kg m2/s2. Symbol is J.


Kilo Electron Volt (keV)

Unit equal to one thousand electron volts. See Electron Volt.


Labeled Compound, Radioactive

A compound consisting in part of molecules containing one or more radioactive atoms. By observations of radioactivity, this compound or its fragments may be followed through physical, chemical, or biological processes.

Laser Safety Officer

Individual who has the authority to monitor and enforce the control of lasers.

Laser System

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


A device that produces an intense, coherent, directional beam of light. Also an acronym for Light Amplification by Stimulated Emission of Radiation.

Loose Surface Contamination

Contamination that is easily removed. Loose contamination must be controlled to minimize internal contamination, spread of contamination to the environment, or contamination of experiments.


Mass Number (A)

The number of nucleons (protons [Z] plus neutrons [N]) in the nucleus of an atom. The mass number is 125 in 125I.

Maximum Permissible Exposure (MPE)

The maximum level of laser radiation to which a human can be exposed without adverse biological effects to the eye or skin.

Mega Electron Volt (MeV)

Unit equal to one million electron volts. See Electron Volt.

Microcurie (μCi)

One-millionth of a curie (37,000 disintegrations per second).

Millicurie (mCi)

One-thousandth of a curie (37,000,000 disintegrations per second).

Milliroentgen (mR)

Unit equal to one one-thousandth (1/1000th) of a roentgen. See Exposure.



(nCi): One-billionth of a curie (37 disintegrations per second).


Uncharged particles with masses approximating those of protons (~ 1 amu). Generated in nuclear fission, fusion, neutron sources, and accelerators.


A species of atom characterized by its mass number, atomic number, and the energy state of its nucleus, provided that the atom is capable of existing for a measurable time.


Optical Density (OD)

A logarithmic expression for the attenuation produced by an attenuating medium, such as an eye protection filter. OD = log10 (Ii/It) where Ii is the incident irradiance and It is the transmitted irradiance.


Permissible Exposure Limits (PELs)

Refers to a time weighted average (TWA) of exposure for an eight-hour workday within a 40-hour workweek. Exceptions are those limits that are given a ceiling value.

Principal Investigator (PI)

In this chapter, synonymous with Authorized User. The person ultimately responsible for radioactive material use in areas under his or her responsibility. See Section 2.3, Principal Investigators.


A container (usually lead) used to ship or store radioactive materials.


A positively charged beta particle. When a positron has expended its kinetic energy, it interacts with an electron and is annihilated, liberating two 0.511 MeV gamma rays.

Protective Housing

A device designed to prevent access to radiant power or energy.


Nuclear particle with a positive electric charge equal numerically to the charge of the electron and a mass of about 1 amu. (1,836 times greater than an electron).

Pulsed Laser

A laser that delivers its energy in the form of a single pulse or a train of pulses, with a pulse duration of less than 0.25 seconds.



A unit of absorbed dose. 1 rad equals 100 ergs of energy absorbed in 1 gram of material, or 0.01 J/Kg of material. See Dose, Absorbed.

Radiant Energy

Laser energy emitted, expressed in joules (J).

Radiant Exposure

Radiant energy per unit area, expressed in joules per square centimeter.

Radiant Power

Laser power emitted, expressed in watts (W).

Radiation, Background

Ionizing radiation arising from radioactive material 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. In Seattle, one receives approximately 100 mrem per year from natural background radiation.

Radiation, External

Radiation from a source outside the body. The radiation must penetrate the dead layer of skin.

Radiation, Internal

Radiation from a source within the body resulting from deposition of radionuclides in body tissue.

Radiation, Ionizing

Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.

Radiation, Scattered

Radiation which has been deviated in direction during its passage through a substance. The radiation may also have been modified by a decrease in energy.


Emission and propagation of energy through space or through a material medium in the form of waves, e.g., the emission and propagation of electromagnetic waves. The term radiation when unqualified usually refers to ionizing radiation. It can also refer to particle emissions, such as alpha, beta and neutron radiation, or cosmic radiation.


The property of certain nuclides of spontaneously emitting particles or gamma radiation, or of emitting x-radiation following orbital electron capture, or of undergoing spontaneous fission.


Used synonymously with radioisotope. A nuclide with an unstable ratio of neutrons to protons placing the nucleus in a state of stress. In an attempt to reorganize to a more stable state, it may undergo various types of rearrangement that involve the release of radiation. Approximately 5,000 natural and artificial radionuclides have been identified.

Relative Biological Effectiveness (RBE)

The ratio of the absorbed dose of a reference radiation that produces a specified biological effect to the absorbed dose of the radiation of interest that produces the same biological effect for a particular living organism or part of an organism.


The special unit of dose equivalent. The dose equivalent in rems is numerically equal to the absorbed dose in rads multiplied by the quality factor, distribution factor, and any other necessary modifying factors. Represents the dose to the body. See Dose Equivalent.


Radioactive Material Memorandum of Understanding and Agreement. An application that investigators at the Hutch must complete before they can begin using radioactive materials. See Section 3, Radioactive Material Memorandum of Understanding and Agreement (RMUA), for explanation.

Roentgen (R)

The measure of radiation exposure in air. One roentgen equals 2.58 x 10-4 coulombs per kilogram of air. See Exposure.


The Fred Hutch Radiation Safety Committee. See Section 2.1, Radiation Safety Committee (RSC), for an explanation of the Committee.


The Radiation Safety Officer. See Section 2.2, Radiation Safety Officer (RSO).


Scanning Laser

A laser having a time-varying direction, origin, or pattern of propagation with respect to a stationary frame of reference.

Scintillation Counter

A counter in which light flashes produced in a solid scintillator (usually a sodium iodide [NaI] crystal) by ionizing radiation are converted into electrical pulses by a photomultiplier tube. The amount of light emitted by the crystal is directly proportional to the amount of energy deposited in the crystal by the radiation. Usually referred to as an NaI probe or NaI detector.

Sealed Source

A radioactive source sealed in an impervious container that has sufficient mechanical strength to prevent contact with or dispersion of the radioactive material under the conditions of use and wear for which it was designed.

Shielding Material

Any material that is used to absorb radiation and thus effectively reduce the intensity of radiation, and in some cases, eliminate it. Lead, concrete, aluminum, water, and plastic are examples of commonly used shielding material.

Smear Test

See Wipe Test.

Specific Activity

Total radioactivity of a given nuclide per gram of a compound, element or radioactive nuclide.

Survey, Radiological

A study to find and quantify the radiation or contamination level of specific objects or locations, and locate regions of higher-than-average intensity of radiation (hot spots).


Thermoluminescent Dosimeter (TLD)

A dosimeter made of certain crystalline material that is capable of both storing a fraction of absorbed ionizing radiation and releasing this energy in the form of visible photons when heated. The amount of light released can be used as a measure of radiation exposure to these crystals. Ring dosimeters worn at the Hutch are TLDs.

Tracer, Isotopic

The isotope or non-natural mixture of isotopes of an element which may be incorporated into a sample to make possible observation of the course of that element, alone or in combination, through a chemical, biological, or physical process. The observations may be made by measurement of radioactivity or of isotopic abundance.


Ultraviolet (UV) Radiation

Electromagnetic radiation with wavelengths between soft x-rays and visible violet light, often broken down into UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm).


Visible Radiation (Light)

Electromagnetic radiation which can be detected by the human eye. It is commonly used to describe wavelengths which lie in the range between 400 nm and 700 nm.



The length of the light wave, usually measured from crest to crest, which determines its color. Common units of measurement are the micrometer (micron) and the nanometer (nm).

Wipe Test or Smear Test

A procedure in which a dry swab (e.g., a circle of filter paper) is rubbed on a surface and its radioactivity is measured to determine whether the surface is contaminated with loose radioactive material.



Penetrating electromagnetic radiations having wavelengths shorter than those of visible light. They are usually produced by bombarding a metallic target with fast electrons in a high vacuum, as in an x-ray machine. In nuclear reactions, it is customary to refer to photons originating in the nucleus as gamma rays, and photons originating in the energy exchanges of electrons as x-rays.