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Radiation Protection Glossary

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Effective dose
The Effective Dose is obtained by taking the Equivalent Dose (Dose Equivalent ) and multiplying by a Tissue Weighting Factor which relates to the organs / tissues under consideration. Effective Dose can therefore also be considered a doubly weighted Absorbed Dose since it takes into account the type of radiation (radiation weighting factor) and the target organ / tissue. The quantity can be used to express Detriment to the whole body as a summation of several different doses of radiation with varying radiation weighting factors (radiation type) and targets.
Electromagnetic spectrum
The electromagnetic spectrum covers a wide range of wavelengths and Photon energies. It ranges from Gamma Rays at one end (High Frequency, High Energy and Low Wave Length) to radio waves at the other (Low Frequency, Low Energy and Long Wave Length).For Ionising Radiation protection purposes we are concerned with X-Rays and Gamma Rays.
Electron
The electron is a low mass particle ( 1/1836 that of a Proton ) with a unit negative electric charge. In simple terms the electrons are said to orbit around the Nucleus of Atoms . Positively charged electrons can also exist, these being known as Positrons . The electron is closely related (identical in fact) to the Beta Particle .
Electron volt
The electron volt (eV) is a unit used in Radiation Protection / Health Physics to describe the energy of Ionising Radiation . The value of the eV is derived from the energy required to accelerate an electron through a potential of 1 volt. In more familiar units the eV is approximately equivalent to 1.6 E-19 joules. In everyday use the units of KeV (or MeV) are used as the eV is obviously an extremely small quantity. In training we often say the eV represents the 'punch' that the ionising radiation has to do work (damage) and so can be related to hazard potential.
Element
An element represents the simplest form of a chemical where all the Atoms share the same Atomic Number . This will include, for example, Hydrogen, Oxygen and Carbon.
Enriched uranium
Uranium where the content U-235 is increased above its natural value of around 0.7% by weight. The enrichment process will also yield Depleted Uranium . Enriched Uranium is Fissile and can undergo nuclear fission under certain conditions, its therefore used in Nuclear Power production and Nuclear Weapons.
Environmental Decontamination
With respect to Radiation Protection , environmental decontamination refers to the systematic clean-up of Radioactive Contamination within the workplace or wider environment. Also see Personal Decontamination .
Environmental Exposure
With respect to Radiation Protection , environmental exposure refers to Ionising Radiation exposure within the workplace or wider environment. Also see Personal Exposure .
EPD
With respect to Radiation Protection , EPD stands for 'Electronic Personal Dosimeter'. A number of types of device can function as an EPD which is a type of Active Dosimeter . It is designed to provide real time information on Dose and Dose Rate .
Equivalent Dose
Equivalent Dose (can be refererd to as Dose Equivalent ) is a quantity which takes into effect 'radiation quality', which relates to the degree to which a type of Ionising Radiation will produce biological damage. Equivalent Dose is obtained by multiplying the Absorbed Dose by a Radiation Weighting Factor or Quality Factor if Dose Equivalent is used . The resulting quantity can then be expressed numerically in Sieverts (Sv) or in the old units of Rem . The quantity is independent of the absorbing material (i.e. tissue).
Erythema
Erythema presents itself as a reddening of the skin which is caused by blood vessel dilation. It is a common sign of Deterministic Radiation Effects , particularly from high energy Beta emitters or X-Rays .
Exemption Orders
Exemption Orders were made under the UK Radioactive Substances Act 1960 as statutory instruments , now superseded by the Radioactive Substances Act 1993 (despite this, the orders remain legally valid). They specify classes of premises, undertakings, entities or persons, and provide descriptions of Radioactive material or radioactive apparatus which do not need to be registered or further authorised under the Act. The orders are designed to maintain control of radioactive materials, without excessive bureaucracy, where there is a clear benefit of use, or where it is reasonable, for example, to make disposals without authorisations.
External Radiation
The external radiation (hazard) exists where an absorber (typically a person) is being exposed to a source of Ionising Radiation external to the body. Examples would include exposures to Sealed Sources , dental X-Rays and Cosmic Rays . One feature of this hazard is that moving the absorber away from the source (usually) results in a reduction in the Dose of ionising radiation to that absorber, which is not the case for Internal Radiation hazards.