ARCHIVE: e-Digest Statistics about: Radioactivity

Definitions

Atomic Structure
Atom
the smallest portion of an element that can combine chemically with other atoms.
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.
Isotope
nuclides with the same number of protons but different numbers of neutrons.
Nuclide
a species of atom characterised by the number of protons and neutrons and, in some cases, by the energy state of the nucleus.
Proton
an elementary particle with unit atomic mass approximately and unit positive electric charge.
 
Radiation
Activity
attribute of an amount of a radionuclide. Describes the rate at which transformations occur in it. Unit becquerel (Bq). 1Bq = 1 nuclear disintegration per second.
Daughter product
the product of the radioactive decay of a radioisotope. For example, radon-226 is the daughter product of the decay of thorium-230.
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.
Half-life
the time taken for the activity of a radionuclide to lose half its value by decay.
Ionising radiation
radiation that produces ionisation in matter. Examples are alpha particles, beta particles, gamma rays, x-rays, and neutrons.
Radioactive
possessing the property of radioactivity.
Radioactivity
the property of radionuclides of spontaneously emitting ionising radiation.
Radiation
the process of emitting energy as waves or particles. The energy thus radiated.
Radionuclide
an unstable nuclide that emits ionising radiation.
Radiotoxicity
effect of radioisotopes becoming bound in the body and producing intense biological damage when they decay.
 
Types of rays
Alpha particle
a particle consisting of two protons plus two neutrons emitted by a radionuclide. They cannot penetrate the skin.
Beta particle
an electron emitted by the nucleus of a radionuclide. The electric charge may be positive (positron). They can penetrate the skin but can be stopped by a few millimetres of metal.
Gamma ray
a discrete quantity of electromagnetic energy, without mass or charge, emitted by a radionuclide. They cannot penetrate lead or a large thickness of concrete. See x-ray.
X-ray
a discrete quantity of electromagnetic energy, without mass or charge, emitted by an x-ray machine. See gamma-ray.
 
Doses
Absorbed dose
quantity of energy imparted by ionising radiation to unit mass of matter such as tissue. Measured in Grays (Gy). 1 Gy = 1 joule per kilogram.
Collective effective dose equivalent (collective dose)
effective dose equivalent to a group from a source of radiation. Measured in man sieverts (man Sv).
Dose equivalent
absorbed dose weighted for harmfulness of different radiations. Measured in sieverts (Sv). Usually the factor for gamma-rays, x-rays and beta particles is 1 but for alpha particles it is 20.
Effective dose equivalent
dose equivalent weighted for susceptibility to harm of different tissues (risk weighting factors). Measured in sieverts (Sv).
 
Specific Radionulides
Argon-41
radioactive isotope of argon, which has a half-life of only 110 minutes. It is produced mainly from the activation of the argon present naturally in the air used to cool the outside surfaces of the reactor vessels and their shields. It is discharged from high stacks to ensure its rapid dispersal in the atmosphere and, being inert, it is not reconcentrated by biological systems.
Caesium-137
radioactive isotope of caesium produced in nuclear reactions, with a half-life of 33 years. It is chemically similar to potassium; when absorbed into the body, it spreads throughout the muscles.
Carbon-14
radioactive isotope of carbon produced in nuclear reactions, with a half-life of 5,730 years.
Iodine-131
radioactive isotope of iodine produced in nuclear reactions, with a half-life of 8 days. Tends to be concentrated in milk. Iodine in the body concentrates in the thyroid gland, which can be damaged by the intake of iodine-131.
Krypton-85
noble gas with a half-life of 10.8 years. Discharged into the atmosphere from nuclear power stations.
Plutonium
element produced in nuclear reactions. It emits alpha particles and accumulates in the liver and skeleton if it enters the bloodstream. It lodges in the lung if inhaled as dust.
Radon
radioactive decay product of naturally-occurring uranium-238. A gas with a half-life of 3.8 days, which can cause lung damage if further radioactive decay occurs while it is in the lung.
Strontium-90
radioactive isotope of strontium produced in nuclear reactions, with a half-life of 28 years. It is chemically similar to calcium and tends to be concentrated in milk. When absorbed into the body, it is concentrated in the bones.
Thorium
element which occurs naturally as thorium-232 and is four times more abundant in the earth's crust than uranium. When bombarded with neutrons, it undergoes a transformation to produce uranium-233, which is highly fissile.
Tritium
radioactive isotope of hydrogen produced in nuclear reactions, with a half-life of 12.3 years. It has a very low radiotoxicity so is not subject to reconcentration in marine organisms and therefore relatively large quantities may be discharged with relatively little radiological effect.
Uranium
radioactive element which occurs naturally as uranium-235 (half-life 7.5 x 108 years) and uranium-238 (half-life 4.5 x 109 years). Neutron absorption by uranium-238 in a nuclear reactor produces plutonium-239.
 
Measurements
The International System (SI) of units for radioactivity, radiation and the effects of radiation are as follows:
Becquerel (Bq)
the standard international unit of radioactivity, corresponding to one nuclear disintegration per second. Multiples of the becquerel are frequently used such as the terabecquerel (TBq) which is 1 million million (1012) becquerels.
Gray (Gy)
the standard unit of absorbed dose, corresponding to 1 joule of energy per kilogram of material.
man Sievert (man Sv)
the unit of measurement of the collective dose.
millisievert (mSv)
unit of effective dose equal to one thousandth (10-3) of a Sievert. Natural radiation and natural radioactivity in the environment give an average effective dose to each member of the public of about 2 mSv per year. The internationally recommended limit for prolonged public exposure to artificial radioactivity is 1 mSv per year.
Sievert (Sv)
standard unit of biologically-effective dose. It is calculated by multiplying the absorbed dose (measured in Grays) by a quality factor which takes account of the differing biological effectiveness of the various types of radiation.
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Page last modified: 16 September 2003
Page published: 10 September 2003