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.