ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

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Absorbed dose

Quantity of energy imparted by ionizing radiation to unit mass of matter such as tissue. Unit gray, symbol Gy. 1 Gy = 1 joule per kilogram.

Activity

Attribute of an amount of a radionuclide. Describes the rate at which transformations occur in it. Unit becquerel, symbol Bq. 1 Bq = 1 transformation per second.

Alpha particle

A particle consisting of two protons plus two neutrons. Emitted by a radionuclide.

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.

Auger Electron

An electron, sometimes emitted from an atom instead of an x-ray that would otherwise carry away the excess energy. Auger electrons are usually of no significance as a radiation hazard but can contribute to radiation dose in the decay of some radionuclides while inside cells in the body, as in radiopharmaceuticals.

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.

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.

Cosmic rays

High energy ionizing radiations from outer space. Complex composition at the surface of the earth.

Cosmogenic radionuclides

The cosmic radiation which strikes the earth induces radioactivity in the atmosphere. Most of this radioactivity is very short-lived. Some radionuclides however survive to eventually reach the surface of the earth. Among these are H (tritium), Be (beryllium-7) and C (carbon-14) which has the longest half-life (5730 years).

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.

Diagnostic radiology

Term usually applied to the use of x-rays in medicine for identifying disease or injury in patients.

Disposal

In relation to radioactive waste, dispersal or emplacement in any medium without the intention of retrieval.

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 ionizing 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.

Electric field strength

A measure of the intensity of an electric field. Unit volt per metre, symbol V m^-1.

Electromagnetic field

The region in which electromagnetic radiation from a source exerts an influence on another object with or without there being contact between them.

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.

Electromagnetic wave

See electromagnetic radiation.

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 × 10^-19 joule approximately.

Element

A substance with atoms all of the same atomic number.

EMF

Electromagnetic field. Not to be confused with the initials for electromotive force.

Equivalent dose

The quantity obtained by multiplying the absorbed dose by a factor to allow for the different effectiveness of the various ionizing radiations in causing harm to tissue. Unit sievert, symbol Sv.

Erythema

Reddening of the skin caused by dilation of blood vessels.

Excitation

A process by which radiation imparts energy to an atom or molecule without causing ionisation. Dissipated as heat in tissue.

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.

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.

Gamma ray

A discrete quantity of electromagnetic energy without mass or charge. Emitted by a radionuclide. See x-ray.

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.

Infrared radiation

Electromagnetic radiation capable of producing the sensation of heat and found between light and radiofrequency radiations in the electromagnetic spectrum. Has subregions IRA, IRB and IRC.

Ion

Electrically charged atom or grouping of atoms.

Ionization

The process by which a neutral atom or molecule acquires or loses an electric charge. The production of ions.

Ionizing radiation

Radiation that produces ionisation in matter. Examples are alpha particles, gamma rays, x-rays and neutrons. When these radiations pass through the tissues of the body, they have sufficient energy to damage DNA.

Isotope

Nuclides with the same number of protons but different numbers of neutrons. Not a synonym for nuclide.

Laser

Device which amplifies light and usually produces an extremely narrow intense beam of a single wavelength.

Light

Electromagnetic radiation capable of producing the sensation of vision and found between ultraviolet and infrared radiations in the electromagnetic spectrum.

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 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.

Photon

A quantum of electromagnetic radiation.

Positron

See beta particle.

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 ionizing radiation except when it is necessary to avoid confusion with non-ionizing radiation.

Radioactive

Possessing the property of radioactivity.

Radioactive waste

Useless material containing radionuclides. Frequently categorised in the nuclear power industry according to activity (and other criteria) as low level, intermediate level and high level waste.

Radioactivity

The property of radionuclides of spontaneously emitting ionizing radiation.

Radiofrequency radiation

Electromagnetic radiation used for telecommunications and found in the electromagnetic spectrum at longer wavelengths than infrared radiation.

RF

See radiofrequency radiation.

Radiological protection

The science and practice of limiting the harm to human beings from radiation.

Radionuclide

An unstable nuclide that emits ionizing 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.

Sievert

See effective dose.

Specific energy absorption rate

The rate at which energy is absorbed by unit mass of tissue in an electromagnetic field. Unit watt per kilogram, symbol W kg^-1.

SAR

See specific energy absorption rate.

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 × 10³ m s^-1.

Ultraviolet radiation

Electromagnetic radiation found between x-rays and light in the electromagnetic spectrum. Has subregions UVA, UVB, UVC.

UV radiation

See ultraviolet radiation.

Visible radiation

See light.

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.

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