The energy deposited
by ionising radiation per unit mass of irradiated material.
The unit is the gray (Gy), and is measured in joules per kilogram.
The number of disintegrations
per unit time taking place in a radioactive material.
The unit of activity is the becquerel (Bq), which represents
one disintegration per second.
The activity per unit
volume or per unit mass of a substance (e.g. Bq/l or Bq/kg)
particle emitted from the nucleus of an atom during radioactive
decay. It consists of 2 protons and 2 neutrons (a helium-4
nucleus). Although alpha particles are normally highly
energetic, they travel only a few centimetres in air and are
stopped by a sheet of paper or the outer layer of dead skin.
The amount of radiation
to which a member of the population is exposed from natural
sources, such as terrestrial radiation due to naturally occurring
radionuclides in the soil, cosmic radiation originating in
outer space, and naturally occurring radionuclides deposited
in the human body, through food, drink and breathing.
A unit of activity,
equal to one radioactive disintegration per second.
A particle emitted
from an atom during radioactive decay. Beta particles
are electrons with either a negative or a positive electric
charge. High energy beta particles may travel metres
in air and several millimetres into the human body; low energy
beta particles are unable to penetrate the skin. Most
beta rays can be stopped by a small thickness of light material,
such as aluminium or plastic sheeting.
For a given source,
the integrated product of effective dose and number of individuals
in the population. The unit is man-Sievert (or man-Sv).
Contamination Back to top
A deposit of dispersed
radioactive material on or within any other medium, such as
land, sea, air, structures, people, vehicles, food, water
An assembly, including
one or several radiation detectors and associated subassemblies,
designed to measure radioactivity per unit surface area associated
with the contamination of the examined object.
Decay (or Radioactive
The radioactive disintegration of an atomic nucleus resulting
in the release of alpha or beta particles, or gamma radiation.
Removal or reduction
of radioactive contamination.
Health effects of which
the probability rises rapidly from zero to unity as the dose
increases above some threshold of dose. The severity
also rises with dose above the threshold.
An instrument that
measure radiation dose.
Effective Dose Back to top
It is equal to the
absorbed dose (in grays) multiplied by the radiation weighting
factor which accounts for the harmfulness of different types
of radiation (alpha, beta or gamma) and multiplied by the
tissue weighting factors which account for the different sensitivities
to radiation induced biological effects of different human
organs or tissues. Its unit is Sievert (Sv), or the
more commonly used millisievert (mSv). The effective
dose represents the total detriment to an individual resulting
from an exposure to ionising radiation. On average,
each individual receive an effective dose of 2.4 mSv every
year from natural background radiation. The effective
dose received in a typical chest X-ray examination is about
Exposure due to ionising
radiation reaching the body from sources outside the body.
Gamma radiation is
short wavelength electromagnetic radiation, of the same physical
nature as light, X-rays, radio waves, etc. However,
gamma radiation is highly penetrating (more so than X-rays)
and, depending on its energy, may require a considerable thickness
of lead or concrete to absorb it. Since gamma radiation
causes ionisation it constitutes a biological hazard.
The effects of an exposure
on humans. These may include deterministic and stochastic
Half-life Back to top
The time required for
a radioactive substance to lose 50% of its activity by decay.
Each radionuclide has a unique half-life.
Energy Agency (IAEA)
Energy Agency, which came into being on 29 July 1957, is an
independent intergovernmental organisation within the United
Nations System. Headquartered in Vienna, Austria, the
Agency has more than 100 Member States who work together to
carry out the main objectives of IAEA's Statute: To
accelerate and enlarge the contribution of atomic energy to
peace, health, and prosperity throughout the world and to
ensure so far as it is able that assistance provided by it,
or at its request or under its supervision or control, is
not used in such a way as to further any military purpose.
on Radiological Protection (ICRP)
recognised organisation whose primary function is to make
recommendations on the various aspects of radiological protection,
based upon which many nations formulate their policy and draft
their legislation in relation to exposure to radiation.
A dose of radiation
delivered by radioactive materials that have been ingested,
inhaled, or incorporated into the body.
Internal Exposure Back to top
Exposure due to radiation
originating from radionuclides taken into the body through
ingestion, inhalation, incorporation, or through wounds.
Radiation capable of
causing ionisation of the matter through which it passes.
Ionising radiation may damage living tissue.
Atoms of an element
having the same number of protons but different number of
neutrons in the nuclei. Different isotopes have the
same chemical properties, but somewhat different physical
properties. Isotopes of an element can be classified
as radioisotopes (those undergoing decay with the emission
of characteristic radiation) or stable isotopes.
One-thousandth of a
The measurement of
radiation or radioactivity, for assessment or control of exposure
to radiation or radioactive materials, and the interpretation
of such measurements.
Nuclide Back to top
A species of atom characterized
by the constitution of its nucleus, which is specified by
its number of protons, number of neutrons and energy content.
A radioactive species
of an atom characterized by the constitution of its nucleus.
Sometimes regarded as an alternative to radioisotope.
In the context of radiation
protection, radiation induced cancer or genetic effects.
The probability of these health effects, rather than their
severity, is a function of radiation dose. It is assumed
that there is no threshold below which stochastic effects
do not occur.
An integrating detector
where radiation energy is absorbed (trapped) and can be read
out later by thermal excitation of the detector. It
is used for estimating the total radiation dose received within
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