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Radiation Worker Glossary
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A device that increases the momentum, and therefore the energy, of charged particlessuch as electrons or protons.

Access Control System

Engineered and/or administrative systems that limit radiation dose to personnel by managing and limiting entry to an area.

Activation (also Radioactivation)

The process of making a material radioactive by bombardment with neutrons, protons, or high energy photons.

Activity (also Radioactivity)

The rate at which a source emits radiation. Activity is measured in terms of the number of disintegrations that take place in some time period (eg. disintegrations per second ). The special unit for activity is the curie. One curie (Ci) is equal to 37 billion (3.7 x 1010) disintegrations per second.

Acute Dose

The absorption of a relatively large amount of radiation over a short period of time.

Acute Radiation Syndrome

The complex of symptoms brought about by excessive exposure to radiation. ARS is the result of an acute dose; some early visible symptoms may include nausea, vomiting, and fatigue, followed by a predictable progression of other deterministic effects depending on the total dose.

Administrative Controls

Procedures and activities which involve human actions that are designed to minimize or control personnel radiation exposure. Examples of administrative controls are Radiation Work Permits, sweep procedures, and TOSPs.


As Low As Reasonably Achievable. Making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical, taking into account the state of technology and other societal and economic considerations, including the benefit of the radiation producing activity.

Alpha Particle

A positively charged particle ejected spontaneously from the nuclei of some radioactive atoms. It is identical to a helium nucleus - it contains two protons and two neutrons.

Assigned Radiation Monitor (ARM)

A person who has received training beyond the Radworker level in the use of radiation protection instrumentation and administrative procedures for controlling exposure to radiation and handling of radioactive material.


The process by which radiation is reduced in intensity when passing through some material. It is the combination of absorption and scattering processes.

Atomic Number (Z number)

The number of protons in the nucleus of an atom.

Atomic Weight See mass number .


Background Radiation

Radiation present in the environment to which all people are exposed. Background radiation comes from natural radioactivity and radiation, and from manmade sources such as global fallout and certain consumer products.


A flow of electromagnetic or particulate radiation that is either unidirectional by nature, or has been collimated or restricted to a small solid angle.

Beam Enclosure

The structure which houses the accelerator and experimental target areas. It is interlocked during accelerator operation to prevent personnel access.


The vacuum chamber in which the beam travels (generally includes associated components of beam transport, such as magnets, beam dumps, accelerating cavities, etc.).

Beta Particle

An energetic electron which is emitted from the nucleus during beta decay.


Photon radiation (x-rays) produced by deceleration of charged particles as they pass through matter.



Controlled Area Radiation Monitor. A radiation detection system which is interlocked to the Personnel Safety System and designed to turn off the electron beam if radiation levels exceed pre-established set points.

Charged Particle

An ion. A particle carrying a positive or negative electric charge.

Chronic Dose

The absorption of a relatively small amount of radiation over a long period of time.


A device which limits the size, shape, and direction of a radiation beam.

Collective Dose

The sum of the individual doses received in a given period of time by a specific group of people. See Person-rem .


The deposition of unwanted radioactive material (usually in an easily removable form) on the surfaces of structures, areas, objects, or personnel.

Controlled Area

Any area where access is controlled to ensure the radiological safety of personnel. Controlled Areas contain radiological hazards which are identified by specific postings. Personnel who work only in a Controlled Area are not expected to receive a dose in excess of 100 mrem/yr. See Radiological Area.

Cumulative Dose

The total dose received over a period of time.

Curie See Activity .


Daughter Product (progeny)

Nuclide (or isotope ) that is formed by the radioactive decay of some other nuclide. For example, the radioactive isotope Cobalt-60 decays to the stable isotope Nickel-60. See Nuclide and Isotope .

Declared Pregnant Worker

A woman who has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception, for the purpose of limiting her exposure to radiation.

Deep Dose

Applies to the measurement of external, whole body radiation exposure - specifically, it is the dose equivalent at a tissue depth of 1 cm. See Whole Body .


A material or device that is sensitive to radiation and can produce a response signal suitable for measurement or analysis.

Deterministic Effect

A biological effect which becomes more severe with an increase in dose. These effects usually have thresholds or minimum values, below which the risk of experiencing the effect is considered to be zero.


A generic term for the amount of radiation absorbed.

Dose equivalent

The product of absorbed dose (i.e. rads) in tissue and quality factor. Dose equivalent is measured in units of rems. It is a description of the dose received by a person in terms of biological effect, rather than strictly energy absorbed.


A device or instrument for measuring integrated (or cumulative) dose.


Electromagnetic Radiation

Radiation having no mass or charge. A traveling wave resulting from changing electric and/or magnetic fields. See Photon .


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

Electron Volt (eV)

Unit of energy equivalent to the energy gained by an electron in passing through a potential difference of one volt. It is used to quantify the energy or momentum possessed by high energy particles or electromagnetic radiation. Typical ionizing radiations are in the thousand (keV) or million (MeV) electron volt range

Engineered Controls

Equipment, structures, and devices which limit or prevent radiation exposure to personnel with little or no human intervention. These controls may be passive (eg. shielding) or active (eg. interlocks) in nature.


Term used generally to describe receiving radiation dose.


A measure of the ionization produced in air by x or gamma radiation. The unit for exposure is the Roentgen (R). Whole body exposure to 1 R of x or gamma radiation results in a dose equivalent of approximately 1 rem.


Gamma Radiation

High energy, short wavelength electromagnetic radiation emitted from the nucleus. Gamma radiation frequently accompanies beta, and alpha emission during radioactive decay.

Genetic Effect (Heritable Effect)

An effect which occurs in a future generation of an exposed person.


High Radiation Area

Any area where a person could receive a whole body dose of 100 mrem in any one hour up to 5000 mrem in any hour. For purposes of posting, an area where the whole body dose rate is (or might be ) between 100 and 5000 mrem/hr. See whole body and whole body dose rate .



Any automatic sensing device that causes a radiation producing device to shut off or prevents access to the hazardous radiation beam while it is present.

Ion See charged particle .

Ionization The separation of orbital electrons from an atom.

Ionizing Radiation

Radiation which has enough energy to ionize the matter through which it passes.


One of two or more atoms of a given element having different numbers of neutrons. Thus, carbon-12, carbon-13, and carbon-14 are isotopes of the element carbon. The numbers 12, 13, and 14 denote the total number of protons and neutrons in the isotope. See Nuclide .


Linear Accelerator (Linac)

A device used to accelerate charged particles in a straight line.


Mass Number

The total number of nucleons (protons and neutrons) in the nucleus of an atom.



An elementary particle with no electrical charge which has approximately the same mass as a proton.


The small, central region of an atom consisting of protons and neutrons (nucleons). The nucleus contains essentially all of the mass of the atom.


General term referring to all known isotopes, groups of isotopes, or a single isotope.



Operational Safety Procedure. An administrative control measure which describes hazards present and what controls are in place to mitigate or minimize the hazards. OSPs are used during routine operations. Generally associated with an operational instruction rather than a purely safety-related procedure. See TOSP.


Person Rem

The cumulative dose received by a group of people. The person-rem total for a given job and time period is the sum of all doses received by all persons involved in the work for that period. See collective dose .

Personnel Safety System (PSS)

An active engineered control system comprised of interlocks, sensors, and other devices which prevents personnel access to the beam enclosure and/or terminates accelerator operation in the event that trip points are exceeded or interlocks are triggered.


A quantum (discrete packet) of electromagnetic energy. Gamma rays and x-rays are examples of photons. It is customary to refer to photons that originate in the nucleus (during radioactive decay) as gamma rays, and those which originate within the electron field, such as bremsstrahlung photons, as X rays.


A positively charged beta particle.

Prompt Radiation

Particulate or electromagnetic radiation resulting from the accelerator beam or interaction of the beam with surrounding matter. Prompt radiation ceases immediately after shut off of the beam.


Quality Factor (Q)

The modifying factor used to derive dose equivalent from absorbed dose. Quality factor is based on the linear energy transfer (LET) of a particular type and energy of radiation and is proportional to the relative biological effectiveness (RBE) of that radiation.



Radiation Absorbed Dose. The special unit of absorbed dose used to quantify the amount of radiation energy absorbed per unit mass of any material. One rad is equal to an absorbed dose of 100 ergs/gram or 0.01J/kg.

Radiation Area

Any area where a person could receive a whole body dose of 5 mrem in any one hour up to 100 mrem in an hour. For purposes of posting, an area where the whole body dose rate is (or might be) between 5 and 100 mrem/hr. See whole body and whole body dose rate .

Radiation Worker

A person who has received specific training and qualifications to make unescorted accesses into the controlled area and perform work of a radiological nature.

Radioactive Material

Any material containing unstable atoms which decay with the release of ionizing radiation.

Radioactive Materials Area

An area in which radioactive materials are used, stored, or handled.

Radiological Area

Any area requiring posting as a Radiation Area, High Radiation Area, Very High Radiation Area, Contamination Area, High Contamintation Area, or Airborne Radioactivity Area. Also used to describe Radiologically Controlled Area.

Radiologically Controlled Area - (RCA)

Any area where a person could receive a dose in excess of 100 mrem/yr. Also called Radiological Area.


A radioactive isotope of an element which decays spontaneously, emitting radiation.


The special unit of any of the quantities expressed as dose equivalent. The unit used to express the amount of biological harm done from chronic exposure to ionizing radiation. The dose equivalent in rems is equal to the absorbed dose in rads multiplied by the quality factor (Q). The dose, measured in rems is not a physical quantity due to the application of the quality factor. It is therefore an expression of relative risk. See quality factor .

Residual Radiation

Radiation resulting from the decay of activated material within the accelerator. Residual radiation persists after beam shut off, and may contribute significantly to the overall dose to radiation workers.


The special unit of exposure. That amount of gamma or x rays which produce ions carrying one electrostatic unit of charge in one cubic centimeter of dry air. See exposure .

Run-Safe Box

A device which is interlocked to the personnel safety system used to display the accelerator machine state and visually warn of an unsafe condition. When armed, pressing the red button on the box causes the PSS to remove beam or power permit.


Radiation Work Permit. An administrative control measure consisting of a set of requirements for protective equipment, dosimetry, entry and stay time restrictions, and work control measures used to limit personnel exposure during work in certain radiological areas.


Self Reading Pocket Dosimeter (SRPD)

Any type of dosimeter which allows the user to directly read the exposure from the device. Examples of SRPDs are pocket ion chambers, neutron bubble dosimeters, and digital electronic dosimeters.

Shallow Dose

Dose equivalent at a tissue depth of 0.007 cm. Shallow dose applies to the skin, not to the whole body .

Sweep or Search

A physical search performed concurrent to establishing an interlocked state within the beam enclosure prior to operating the accelerator.

Somatic Effect

An effect which occurs in an individual or population exposed (to radiation), as opposed to effects which occur in future generations.

Stochastic Effect

Health effects which occur 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. Examples of stochastic effects are cancer incidence and heritable effects.



Thermoluminescent Dosimeter. TLDs are used as the primary means of recording exposure to radiation. It may be "read" only by specialized processing equipment.


Temporary Operational Safety Procedure. An administrative control measure which describes hazards present and what controls are in place to mitigate or minimize the hazards. TOSPs are used during non-routine operations or temporary configurations of equipment or systems such as special tests or commissioning activities.


Very High Radiation Area

An area where the dose rate exceeds 500 rad/hr a meter from the source. At Jefferson Lab, a more conservative definition is used - an area where the whole body dose rate is (or might be) above 5000 mrem/hr. See whole body and whole body dose rate.


Whole Body

The portion of the body consisting of the head, trunk and major blood forming organs extending to the arms just below the elbow and the legs just below the knee. Whole body dose occurs when any of these portions of the body receive a deep dose.

Whole Body Dose Rate

Radiation level measured at a point 30 cm (~ 1 foot) from the source of radiation or from any surface through which radiation emanates.


X rays (also see photon )

Penetrating electromagnetic radiation (photons) with a wavelength much shorter than visible light.

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