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A1 values and A2 values

Values for the classification of radioactive substances for transportation purposes.

 

Ablation

The functional destruction of an organ through surgery or exposure to large doses of radiation.

 

Absorbed dose

The absorbed dose is the amount of energy absorbed per unit mass of a specific absorbing medium by Ionising Radiation. The regulations use the term absorbed dose for doses to a tissue or to an organ. The unit for absorbed dose is the gray (Gy) where 1 Gy is equal to 1 joule per kilogram (J/kg).

 

Absorbed Dose Rate 

Equals absorbed dose divided by the time taken to deliver that dose. High dose rates are usually more damaging to humans and animals than low dose rates. This is because repair of damage is more efficient when the dose rate is low.

 

Absorber 

Any material that absorbs or lessens the intensity of ionising radiation. Neutron absorbers (like boron, hafnium, and cadmium) are used in control rods for reactors. Concrete and steel absorb gamma rays and neutrons in reactor shields. A thin sheet of paper or metal will absorb or weaken alpha particles and all except the most energetic beta particles.

 

Absorption

Depending on the context, the term absorption has different meanings. It is either: 

• The retention, in a material, of energy removed from radiation passing through it.
• The removal of radiation or the reduction of its energy on passing through matter.
• The process whereby a neutron (or other particle) is captured by a nucleus.
• The uptake of a radionuclide by body organs or tissues.

 

ABWR

Advanced Boiling Water Reactor. This is an evolution of the BWR design. 

 

Accelerator

Equipment or installation in which particles are accelerated, emitting ionising radiation with energy higher than 1 mega-electron volt (MeV)

 

Access Hatch (air lock) 

 An airtight door system that preserves the pressure integrity of a reactor containment building while allowing access to personnel and equipment.

 

Accidental exposure

Exposure of individuals, other than emergency workers, as a result of an accident

 

ACOP

Approved Code of Practice

 

Actinides / Actinoids

A group of 15 chemical elements with atomic number from that of actinium (89) to lawrencium (103) inclusive. All are radioactive. Group includes uranium, plutonium, americium and curium. As a group they are significant largely because of their toxicity. Although several members of the group including uranium occur naturally, most are man-made.

 

Activation

Activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited sites. The excited nucleus decays immediately with the emission of radiation and normally results in the formation of an unstable activation product.

 

Activation product

Radionuclide formed as a result of activation, for example following a neutron capture reaction.

 

Activation cross-section

See cross-section.

 

Active detector

An active detector provides real time measurements of radioactivity or radiation levels. These are typically installed or hand held instruments.

 

Active dosimeter

An active dosimeter is used in dosimetry to measure radiation doses in real time. (Also see EPD).

 

Activity

The number of nuclear transformations occurring in a given quantity of material per unit of time. Normally measured in units of becquerel (Bq) nowadays in most countries. Historical records and the United States may use the curie (Ci). 

 

Activity Concentration 

Radioactivity per mass or volume. The units of activity are the curie (Ci) in the traditional system and the becquerel (Bq) in the international system and are often expressed in a modified manner, such as millicurie (mCi) or megabecquerel (MBq). Masses and volumes of carrier materials are expressed in many forms, such as kilograms (kg) of soil and milliliters (mL) of water or air. The combined result as an activity concentration is activity per mass or volume, such as pCi/kg or Bq/mL.

 

Acute

An event occurring over a very short period of time; less than two weeks in duration, but typically less than 1 day.

 

Acute exposure

A large exposure (typically greater than 0.1 Gy) received over a short period of time (typically less than 1 day).

 

Acute Health Effects 

Prompt radiation effects (those that would be observable within a short period of time) for which the severity of the effect varies with the dose, and for which a practical threshold exists.

 

ADC

Analogue to digital converter. Electronic device used to produce a digital signal which is proportional to the amplitude of an input pulse originating, for example, from a radiation detector.

 

Added Filtration 

Any filtration that is in addition to the inherent filtration.

 

ADR

European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR) 2015 Edition. (Accord européen relatif au transport international des marchandises Dangereuses par Route)

 

ADS

Approved Dosimetry Service (ADS) means a dosimetry service approved in accordance with regulation 36 (Approval of dosimetry services) of the Ionising Radiations Regulations 2017 (IRR17)

 

Adult 

An individual 18 or more years of age.

 

Aerosol

An aerosol is a suspension of solid or liquid particles or particulate in a gas such as air. A common example of an aerosol is dust. 

 

AGR

Advanced gas cooled reactor

 

Air Kerma 

Kerma in a given mass of air. The unit used to measure the quantity of air kerma is the gray (Gy). For X-rays with energies <300 kiloelectronvolts (keV), 1 Gy = 100 rad. In air, 1 Gy of absorbed dose is delivered by 114 roentgens (R) of exposure.

 

Air Sampler 

Apparatus used for air sampling.

 

Air Sampling

A system to sample air for radioactivity then retrospectively assess the concentration of radioactivity in air based on the amount of radioactivity deposited on a filter.

 

Air monitoring

A system to monitor, in real time, the concentration of radioactivity in air. These air monitoring systems are often programmable such that alarms can be sounded if specific concentrations are exceeded.

 

Airborne Radioactive Material 

Radioactive material dispersed in the air in the form of dusts, fumes, particulates, mists, vapors, or gases.

 

ALARA 

Acronym for "As Low As Is Reasonably Achievable". Making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical consistent with the purpose for which the activity is undertaken, taking into account the state of technology, the economics of improvements in relation to the state of technology, the economics of improvements in relation to benefits to the public health and safety, and other societal and socioeconomic considerations, and in relation to utilization of nuclear energy and radioactive materials in the public interest.

 

ALARP

As low as is reasonably practicable

 

ALI

Annual Limit on Intake. A secondary quantity used in internal radiation protection. It is defined as the intake of a radionuclide which would result in a committed effective dose equal to the dose limit.

 

Alpha decay

Radioactive decay resulting in the emission of alpha particle.

 

Alpha emitter

A radionuclide which decays by emission of an alpha particle.

 

Alpha Particle

An ionising particle consisting of two protons and two neutrons. It is a helium (⁴He) nucleus and has a double positive charge (i.e. a helium atom stripped of its two orbiting electrons). Alpha particles are emitted by some heavy elements that include uranium, plutonium and radon. Alpha radiation has greater ionising ability but less penetrating ability than beta or gamma radiation. Alpha particles can be stopped easily, for example, by a piece of paper or the dead protective layer of the skin and are only a concern when alpha-emitting isotopes are taken into the body (e.g., by inhalation).

 

Aluminum Equivalent 

The thickness of type 1100 aluminum alloy affording the same attenuation, under specified conditions, as the material in question.

 

AMAD

Activity median aerodynamic diameter (for aerosol particles). The diameter of a unit density sphere with the same terminal settling velocity in air as that of the aerosol particle whose activity is the median for the entire aerosol.

 

AmBe

Americium-241 beryllium. This is a neutron emitting source commonly used in industry.

 

Ambient dose equivalent

Ambient dose equivalent is the dose equivalent at a point in a radiation field that would be produced by the corresponding expanded and aligned field in the ICRU sphere at a depth, d, on the radius opposing the direction of the aligned field and is given in sieverts.

 

AMR

Advanced Modular Reactor

 

AMU

Atomic mass unit. One-twelfth of the mass of an atom of carbon 12 (C-12). Approximately 1.66x10^-27 kg.

 

Analytical X-Ray Equipment 

Equipment used for X-ray diffraction or fluorescence analysis.

 

Analytical X-Ray System 

A group of components utilizing X- or gamma rays to determine the elemental composition or to examine the microstructure of materials.

 

AN(DG)R

Air Navigation (Dangerous Goods) Regulations 2002

 

Anion 

An ion with more electrons than protons. A negatively charged ion.

 

Annihilation photons

See annihilation radiation

 

Annihilation radiation

The electromagnetic radiation resulting from the mutual annihilation of two particles of the opposite charge. In the case of a collision between an electron and a positron, the annihilation radiation consists of two photons, each of energy of about 0.511 MeV, emitted in directions opposite to each other.

 

Annual dose

Total radiation dose received by an individual in one calendar year.

 

Annual Reference Levels of Intake (ARLI) 

The activity of a radionuclide that, taken into the body during a year, would provide a committed effective dose to a person, represented by reference man, equal to 20 mSv. The ARLI is expressed in becquerels (Bq).

 

ANO

Air Navigation Order 2016

 

Anode 

Positive electrode. The electron-collecting end of an electron tube.

 

Anthropogenic radiation

Radiation which is man-made.

 

Anthropogenic radionuclides

Radionuclides introduced into nature by man.

 

Anticoincidence counting

See coincidence counting.

 

Antineutrino

Particle with no mass, charge or spin which is emitted in beta minus (β^-) decay. The antineutrino and the neutrino emitted in beta plus (β⁺) decay are referred to collectively as electron neutrinos.

 

Appointed doctor

An appointed doctor means a registered medical practitioner who meets such recognition criteria as may from time to time be specified in writing by the Executive. (Definition from IRR17. Executive meaning the HSE for Great Britain and HSE(NI) for Northern Ireland)

 

Area Badge 

A passive radiation monitoring device, such as a thermoluminescent dosimeter, placed in a fixed location for a specified period of time to determine the average dose rate.

 

Area Source 

A radiation source that may be described as two-dimensional, such as a spill of a radioactive solution on a floor.

 

ARSAC

Administration of Radioactive Substances Advisory Committee

 

ARTEMIS

Integrated Review Service for Radioactive Waste and Spent Fuel Management, Decommissioning and Remediation

 

Atom

A unit of matter consisting of a single nucleus surrounded by one or more orbital electrons. The number of electrons is normally sufficient to make the atom electrically neutral. 

 

Atomic

Of, relating to, or concerning atoms.

 

Atomic Energy 

Energy released in nuclear reactions. Of particular interest is the energy released when a neutron initiates the breaking up or fissioning of an atom’s nucleus into smaller pieces (fission), or when two nuclei are joined together under millions of degrees of heat (fusion). It is more correctly called “nuclear energy.”

 

Atomic Mass 

The mass of an isotope of an element expressed in atomic mass units.

 

Atomic Mass Number (A) 

The number of nucleons (protons and neutrons) in the nucleus of an atom. It is the whole number nearest to the atomic mass of the atom, measured in atomic mass units. Sometimes simply called mass number.

 

Atomic Mass Unit (amu) 

A unit of mass, used to express weights of atoms, molecules, or subatomic particles. Equal to one-twelfth the mass of an atom of the most abundant carbon isotope, carbon-12, or 1.66 × 10⁻⁴ g. Also called unified atomic mass unit or dalton.

 

Atomic Number (Z)

The number of protons in the nucleus of an atom. Symbol Z. This number is characteristic of that element.

 

Attenuation

The process by which a beam of radiation is reduced in intensity when passing through some material. It is the combination of absorption and scattering processes and leads to a decrease in flux density of the beam when projected through matter.

 

Attenuation Coefficient 

Of a substance, for a parallel beam of specified radiation: the quantity µ, in the expression µdx for the fraction removed by attenuation in passing through a thin layer of thickness dx of that substance. It is a function of the energy of the radiation. As dx is expressed in terms of length, mass per unit area, moles, or atoms per unit area, µ is called the linear, mass, molar, or atomic attenuation coefficient, respectively.

 

ATTILA

A 3D deterministic code that solves the Boltzmann Transport Equation on a finite element mesh. It and other 3D deterministic codes can be used as an alternative to Monte Carlo codes.

 

Auger electrons

Those electrons emitted from an atom due to the filling of a vacancy in an inner electron shell. Electron emitted in competition with X-ray emission during rearrangement of orbital electrons. Energy normally released as an X-ray is transferred to another outer electron that is ejected from the atom. Auger electrons are monoenergetic. The Auger effect dominates in the light elements, whereas X-ray emission is dominant in the heavier elements.

 

Auger transition

A process by which electrons with characteristic energies are ejected from atoms in response to a downward transition by another electron in the atom.

 

AURPO

Association of University Radiation Protection Officers

 

Automatic exposure control (AEC)

A device for automatically terminating an exposure to radiation when the dose to the image device receptor reaches a pre-set level.

 

Authorised discharge

A discharge to the environment (e.g. gases released through a stack, liquids released to sea, etc) of radioactivity which has been authorised by a regulator in a permit or authorisation.

 

Averted dose

The reduction in radiation dose (dose avoided) by implementation of protective actions.