Glossary

Activity: A measure of the amount of radioactive material. Describes the rate at which radioactive decay ocurrs. Unit becquerel, symbol Bq. 1 Bq = 1 radioactive decay per second.
ALARP: "As Low As Reasonably Practicable" The principle that radiation exposures must be reduced to the lowest level that can reasonably be acheived.
Alpha radiation: The emission of an alpha particle from an atom. Alpha Particle = 2 protons and 2 neutrons
Atom: The smallest portion of an element that can combine chemically with other atoms.
Atomic mass: The mass of an isotope of an element expressed in atomic mass units, which are defined as one-twelfth of the mass of an atom of carbon-12.
Atomic number: The number of protons in the nucleus of an atom. Symbol Z.

Becquerel: See activity.
Beta particle: An electron emitted by the nucleus of a radionuclide. The electric charge may be positive, in which case the beta particle is called a positron.
Brachytherapy: Term applied to the use of radiation sources in or on the body for treating certain types of cancer.
Bremsstrahlung: X-rays generated when high energy electrons such as beta particles are slowed down in a medium.

Chromosomes: Rod-shaped bodies found in the nucleus of cells in the body. They contain the genes, or hereditary constituents. Human beings possess 23 pairs.
Classified persons: Person who is designated as classified under the Ionising Radiations Regulations, 1999, on the basis of the dose they are likely to receive. Must have their dose properly assessed, eg, by personal dosimetry, doses recorded in long-term dose records, and have an appropriate health record.
Collective dose: Frequently used for collective effective dose.
Collective effective dose: The quantity obtained by multiplying the average effective dose by the number of people exposed to a given source of ionising radiation. Unit man sievert, symbol man Sv. Frequently abbreviated to collective dose.
Consumer products: Personal and household goods such as timepieces, smoke alarms, and gas mantles that contain radioactive material for functional reasons.
Contamination: Loose, unsealed radioactive material.
Controlled area: Area designated in accordance with the Ionising Radiations Regulations, 1999. Must be physically demarcated, have access restricted and be described in the Local Rules. Entry into controlled areas allowed for classified persons, and non-classified persons who are working under written arrangements.
Cosmic rays: High energy ionising radiations from outer space. Complex composition at the surface of the earth.
Current density: The electric current or flow of electric charge through a conducting medium, such as tissue, per unit cross-sectional area. Unit ampere per square metre, symbol A m ^-2.

Decay: The process of spontaneous transformation of a radionuclide. The decrease in the activity of a radioactive substance.
Decay product: A nuclide or radionuclide produced by decay. It may be formed directly from a radionuclide or as a result of a series of successive decays through several radionuclides.
Deterministic effects: Health effects that only appear if a threshold level of dose is eceeded, eg radiation-induced erythema (burns). Deterministic effects will appear within the hours, days or weeks following a high radiation exposure.
Diagnostic radiology: Term usually applied to the use of x-rays in medicine for identifying disease or injury in patients.
DNA: Deoxyribonucleic acid. The compound that controls the structure and function of cells and is the material of inheritance.
Dose: General term for quantity of ionising radiation. See absorbed dose, equivalent dose, effective dose and collective effective dose. Frequently used for effective dose.

Effective dose: The quantity obtained by multiplying the equivalent dose to various tissues and organs by a weighting factor appropriate to each and summing the products. Unit sievert, symbol Sv. Frequently abbreviated to dose.
Electrical interaction: A force of repulsion acting between electric charges of like sign and a force of attraction acting between electric charges of unlike sign.
Electromagnetic radiation: Radiation that can be considered as a wave of electric and magnetic energy travelling through a vacuum or a material. Examples are gamma rays, x-rays, ultraviolet radiation, light, infrared radiation and radiofrequency radiation.
Electromagnetic spectrum: All electromagnetic radiations displayed as a continuum in order of increasing frequency or decreasing wavelength.
Electron: An elementary particle with low mass, ¹/₁₈₃₆ that of a proton, and unit negative electric charge. Positively charged electrons, called positrons, also exist. See also beta particle.
Electron volt: Unit of energy employed in radiation physics. Equal to the energy gained by an electron in passing through a potential difference of 1 volt. Symbol eV. 1 eV = 1.6 x 10 ^-19 joule approximately.
Element: A substance with atoms all of the same atomic number.
Equivalent dose: The quantity obtained by multiplying the absorbed dose by a factor to allow for the different effectiveness of the various ionising radiations in causing harm to tissue. Unit sievert, symbol Sv.
Erythema: Reddening of the skin caused by dilation of blood vessels.

Fallout: The transfer of radionuclides produced by nuclear weapons from the atmosphere to earth; the material transferred.
Fast neutrons: Conventionally, neutrons with energies in excess of 0.1 MeV. Corresponding velocity of about 4 x 10 ⁶ m s ^-1
Fast reactors: See nuclear reactor.
Fission: Nuclear fission. A process in which a nucleus splits into two or more nuclei and energy is released. Frequently refers to the splitting of a nucleus of uranium-235 into two approximately equal parts by a thermal neutron with emission of other neutrons.
Fission products: Nuclides or radionuclides produced as a result of fission.
Free radical: A grouping of atoms that normally exists in combination with other atoms but can sometimes exist independently. Generally very reactive in a chemical sense.
Frequency: The number of complete cycles of an electromagnetic wave in a second. Unit hertz, symbol Hz. 1 Hz = 1 cycle per second.
Fusion: Thermonuclear fusion. A process in which two or more light nuclei are formed into a heavier nucleus and energy is released.

Gamma ray: A discrete quantity of electromagnetic energy without mass or charge. Emitted by a radionuclide. See x-ray.
Geiger-Müller tube: A glass or metal envelope containing a gas at low pressure and two electrodes. Ionising radiation causes discharges, which are registered as electric pulses in a counter. The number of pulses is related to dose.
Genes: The biological units of heredity. They are arranged along the length of chromosomes.
Gray: See absorbed dose.

Half-life: The time taken for the activity of a radionuclide to lose half its value by decay. Symbol t ½.

ICRP: International Commission on Radiological Protection. International body of experts which makes recommendations on radiation protection standards.
Ion: Electrically charged atom or grouping of atoms.
Ionisation: The process by which a neutral atom or molecule acquires or loses an electric charge. The production of ions.
Ionising radiation: Radiation that produces ionisation in matter. Examples are alpha, beta, gamma and x-radiation and neutrons. When these radiations pass through the tissues of the body, they have sufficient energy to damage DNA.
IRR 99: The Ionising Radiations Regulations 1999. Legislation enforced by the Health and Safety Executive, that aims to protect workers and others from the health effects of exposure to ionising radiation in the workplace.
Isotope: Nuclides with the same number of protons but different numbers of neutrons. Not a synonym for nuclide.

Local Rules: Set of working procedures written in accordance with the Ionising Radiations Regulations, 1999, to enable work with ionising radiations to proceed safely, and in accordance with the Health and Safety at Work Act, 1974.

Man sievert: See collective effective dose.
Mass number: The number of protons plus neutrons in the nucleus of an atom. Symbol A.
Molecule: The smallest portion of a substance that can exist by itself and retain the properties of the substance.
Mutation: A chemical change in the DNA in the nucleus of a cell. Mutations in sperm or egg cells or their precursors may lead to inherited effects in children. Mutations in body cells may lead to effects in the individual.

Neutron: An elementary particle with unit atomic mass approximately and no electric charge.
Non-ionising radiation: Radiation that does not produce ionisation in matter. Examples are ultraviolet radiation, light, infrared radiation and radiofrequency radiation. When these radiations pass through the tissues of the body they do not have sufficient energy to damage DNA directly.
Nuclear fuel cycle: The stages in which the fuel for nuclear reactors is first prepared, then used, and later reprocessed for possible use again. Waste management is also considered part of the cycle.
Nuclear medicine: Term usually applied to the use of radionuclides for diagnosing or treating disease in patients.
Nuclear power: Power obtained from the operation of a nuclear reactor.
Nuclear power industry: The industry associated with the production of nuclear power. In the UK, the preparation of fuel for nuclear reactors, the operation of reactors, the subsequent reprocessing of the fuel, and the disposal of radioactive wastes.
Nuclear reactor: A device in which nuclear fission can be sustained in a self-supporting chain reaction involving neutrons. In thermal reactors, fission is brought about by thermal neutrons.
Nucleus: The core of an atom, occupying little of the volume, containing most of the mass, and bearing positive electric charge.
Nucleus of a cell: The controlling centre of the basic unit of tissue. Contains the important material DNA.
Nuclide: A species of atom characterised by the number of protons and neutrons and, in some cases, by the energy state of the nucleus.

Optical radiation: Electromagnetic radiation comprising ultraviolet, visible and infrared radiations.
Order of magnitude: Quantity given to the nearest power of ten. A factor of ten or so.

Photographic film: Film with emulsion sensitive to ionising radiation. The degree of blackening is related to dose.
Photon: A quantum of electromagnetic radiation.
Prior Risk assessment: Defined in the Ionising Radiations Regulations 1999, an assessment made by the employer to determine whether he should take any further steps to restrict radiation exposures.
Probability: The mathematical chance that a given event will occur.
Proton: An elementary particle with unit atomic mass approximately and unit positive electric charge.

Radiation: The process of emitting energy as waves or particles. The energy thus radiated. Frequently used for ionising radiation except when it is necessary to avoid confusion with non-ionising radiation.
RPA: Radiation Protection Adviser. Person deemed to be competent to give radiation protection advice, under one of the schemes recognised by HSE.
RPA Body: A body recognised by HSE as having the requisite collective experience and quality assurance systems to provide sound radiation protection advice.
RPS: Radiation Protection Supervisor. Person appointed by the employer to supervise the radiation work, to ensure that local rules are followed.
Radioactive: Possessing the property of radioactivity.
Radioactivity: The property of radionuclides of spontaneously emitting ionising radiation.
Radiobiology: The study of the effects of ionising radiation on living things.
Radiofrequency radiation: Electromagnetic radiation used for telecommunications and found in the electromagnetic spectrum at longer wavelengths than infrared radiation.
Radiological protection: The science and practice of limiting the harm to human beings from radiation.
Radionuclide: An unstable nuclide that emits ionising radiation.
Radiotherapy: Term applied to the use of radiation beams for treating disease, usually cancers, in patients.
Risk: The probability of injury, harm or damage.
Risk factor: The probability of cancer and leukaemia or hereditary damage per unit equivalent dose. Usually refers to fatal malignant diseases and serious hereditary damage. Unit Sv ^-1.

Sealed source: A radioactive source that is contained, or otherwise constructed so as to prevent loss of the radioactive material.
Scintillation counter: A device containing material that emits light flashes when exposed to ionising radiation. The flashes are converted to electric pulses and counted. The number of pulses is related to dose.
Sievert: See effective dose.
Silicon diode: A device made of a silicon compound in which current flows when exposed to ionising radiation. The current is converted to electrical pulses and counted. The number of pulses is related to dose.
Stochastic effect: Health effect whose probability of occurrence depends on the dose received. Ocurrance is usually many years after the exposure, and there is believed to be no threshold level of dose below which no effect will occur.
Supervised area: Area designated in accordance with the Ionising Radiations Regulations, 1999. Supervised area need not be physically demarcated and access is unrestriced. Supervised areas must be descibed in the local rules.

Thermal neutrons: Neutrons that have been slowed to the degree that they have the same average thermal energy as the atoms or molecules through which they are passing. The average energy of neutrons at ordinary temperatures is about 0.025 eV, corresponding to an average velocity of 2.2 x 10 ³ m s ^-1.
Thermal reactor: See nuclear reactor.
Thermoluminescent material: Material which, having been irradiated, releases light in proportion to the ionising radiation absorbed when it is subsequently heated.

Ultraviolet radiation: Electromagnetic radiation found between x-rays and light in the electromagnetic spectrum. Has subregions UVA, UVB, UVC.
Unsealed radioactive materials: Radioactive material that is not designed to be contained. eg. radioactive gas, liquids or powder.
UVR: See ultraviolet radiation.

Waste management: The control of radioactive waste from creation to disposal.
Wavelength: The distance between successive crests of an electromagnetic wave passing through a given material. Unit metre, symbol m.

X-ray: A discrete quantity of electromagnetic energy without mass or charge. Emitted by an x-ray machine. See gamma ray.
X-ray tube: Device that produces X-rays by accelarating electrons through an evacuated tube, onto a heavy target. Requires an electric current.

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