Absorbed DoseQuantity of ionising radiation energy, transmitted to a substance. Measure units are Gray and rad. ActivityRadioactivity measure for any amount of radionuclide. The amount of a radioactive substance is measured not only in measure units (gram, milligram, etc.) but also by its activity, which equals the number of nuclear transformations (decays) in a time unit. The more nuclear transformations the atoms of a certain substance undergo in a second, the higher is its activity and the greater danger it can pose to human beings.
Activity measure unit in the Si (Si - the International System of Units, the most widely used system of units) is the decay per second (decay/sec). This unit is called Becquerel (Bq).
The most widely used external activity unit is curie (Ci), which corresponds the activity of 1 gram of radium. 1 Ci=3,7x10 E10 Bq. Allowable levelsRadionuclide and other content in food, which is considered to be without risk for health. Alpha, beta and gamma raysRadioactive substances emit different types of radiation, which have different ranges. Iodine-131 and caesium-137, for example, are gamma-emitters. Strontium-90, on the other hand, is a beta-emitter.
Alpha particle: A positively charged particle ejected spontaneously from the nucleus (see atom) of some radioactive elements. It has low penetrating power and a short range (a few centimeters in air). The most energetic alpha particle can be easily stopped by a sheet of paper. Alpha particles are hazardous when an alpha-emitting isotope is inside the body.
Beta particle: A charged particle emitted from a nucleus during radioactive decay. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron. Large amounts of beta radiation may cause skin burns, and beta emitters are harmful if they enter the body. Beta particles may be stopped by thin sheets of metal or plastic.
Gamma radiation: High-energy, short wavelength, electromagnetic radiation emitted from the nucleus of radioacitve elements. Gamma radiation frequently accompanies alpha and beta emissions. Gamma rays are very penetrating and are best stopped or shielded by dense materials, such as lead or depleted uranium. Gamma rays are similar to x-rays. AtomThe smallest particle of an element that cannot be divided or broken up by chemical means. It consists of a central core of protons and neutrons, called the nucleus. Electrons revolve in orbits in the region surrounding the nucleus.
Background radiationSum of radiation from cosmic sources, elements in the environment such as natural uranium and radon as well as from global fallout from the testing of atomic bombs. In Germany, the average background radiation exposure is 2.4 mSv per year at sea level. With the exception of individual regions where exposure to radiation is particularly high because of the presence of large quantities of radioactive substances in the soil, this value applies to most parts of the world.
Becquerel (Bq)International System unit of radioactivity, measuring the rate at which atoms decay. 1 Bq is equivalent to one disintegration per second. The activity is usually expressed in relation to one cubic metre (m3) of air or one kilogram (kg) of food. Becquerels can indicate the activity of all the radioactive substances in a sample, or - and this is the more common procedure - the activity of a particular radioactive element such as caesium-137. Instead of the becquerel, the old unit, the curie (Ci) is often still used.Boiling-water reactorA nuclear reactor in which the water used as a coolant boils and the turbines are driven directly by the steam generated. Reactor 4 in Chernobyl was of this type.
Caesium/Caesium-137The most widely distributed long-lived radioactive element (half-life 30 years) following the Chernobyl accident. The measurements and maps of the contaminated territories in Belarus, Russia and Ukraine therefore relate to caesium-137. The names of radioactive substances are often given as follows: the chemical symbol for caesium (Cs) is followed by the atomic mass: Cs-137.Control rodA usually rod-shaped device which is used to control the chain reaction, a sort of "brake" for the nuclear reactor. Control rods consist of neutron-absorbing material, such as boron, cadmium, rare-earth elements and their compounds. As control rods are lowered into the core, the number of neutrons available is reduced and the chain reaction stops.Curie (Ci)The old, but still used, unit of activity, measuring the rate at which atoms decay. 1 Ci is equivalent to 3.7x1010 Bq or 1 Bq = 2.7x10-11 Ci (27 picocuries).
DecontaminationThe complete or partial removal of contamination (= undesired radioactive material) from structures, areas, objects, or people using chemical or physical processes.Deterministic radiation effectsClinically recognisable harmful biological effects, caused by ionising radiation. A threshold in relation to those effects is presumed; if they are lower, there is no effect, if they are higher the seriousness of the effect depends on the dose. Among the deterministic threshold effects are, in particular, radiation sickness, anomalies in fetation, etc. Dose rateRadiation dose in a time unit (second and derived). DosimeterInstrument used to measure the dose of radiation; see absorbed dose
Effective (equivalent) annual doseSum of the effective (equivalent) external human irradiation dose received in one calendar year and expected effective (equivalent) internal irradiation dose, caused by radionuclides absorbed by the organism within that year. The unit for the annual effective dose is Sievert (Sv). Effective doseIonising radiation effect quantity used to measure the risk of long-term radiation consequences for the human organism and its organs considering their radiation sensitivity. The effective dose unit is Sievert (Sv). The traditional unit is rem. Equivalent doseDose absorbed in an organ or tissue multiplied by the corresponding weighting coefficient for the given radiation type. It takes into account the biological effectiveness of different ionising radiation types, as at the same absorbed dose, the alpha, beta and gamma rays do not have the same effects.
The relative biological radiation activity is characterised by the quality coefficient (k), reflecting the ability of the given radiation type to destroy organic tissue. The equivalent dose measure unit in SI is Sievert (Sv). 1Sv=1J/kg = k x 1 Gy, that is the equivalent dose of 1 Sv corresponds the absorbed dose of 1 Gy ionising radiation of which the quality coefficient equals 1. The traditional unit, replaced by Sievert, of the equivalent dose is rem, the biological equivalent to roentgen. 1 Sv = 100 rem.
Food chainThe passway by which certain substances follow to the organism through food.. The food chain starts with plants and passes on to bigger animals and to humans.
Genetic consequences of exposure to radiationConsequences for the descendents because of the exposure of their parents sex cells to radiation. The risk of genetic consequences of exposure to radiation is several times less, than the risk of cancer. Gray (Gy)SI unit for measuring the absorbed dose. 1 Gy is the absorbtion of 1 joule of radiation energy by 1 kilogram of matter (1 Gy = 1J/kg). Before, the traditional unit rad was used.
Half-lifeA measure of how long a radioactive substance represents a problem in the environment. For example, the half-life of caesium-137, the most widely distributed element after the Chernobyl accident, is about 30 years. This means that after 30 years, half of the radioactive atoms in a given quantity of caesium will have decayed. After another 30 years, the acitivty will be reduced to a quarter of the original intensity, and so on. Iodine-131, another element released in the nuclear accident, has a half-life of only 8 days and had thus decayed almost completely after a few months.Hot spotThe region in a radiatively contaminated area where the level of radiation/contamination is significantly greater than in neighbouring regions in the area.
IodineOne of the radioactive elements released into the environment following the nuclear accident at Chernobyl. In terms of radiation exposure, iodine, with a half-life of 8 days, posed the greatest immediate risk. In Belarus, for example, in the first week after the accident, increased iodine levels were measured almost everywhere. The human body cannot distinguish radioactive iodine from its natural, stable counterpart, and stores it primarily in the thyroid gland. Iodine is considered to be responsible for the dramatic rise in the incidence of thyroid cancer, especially among children and adolescents, following Chernobyl.Ionising radiationRadiation whose interaction with the environment leads to a ionisation of its atoms and molecules. Ionising radiation includes gamma rays, roentgen rays, cathode, positron, neutron and alpha particle beams. Ionising radiation sourceDevice or radioactive material, which emits or is able to emit ionising radiation. Ionising radiation sources are divided into natural and artificial (created by humans, man-caused). Different types of cosmic radiation and natural radionuclides in the earth crust, in the environment, in plants and in animals including in the human organism belong to the natural ionising radiation sources.
The radiation dose on humans due to the natural ionising radiation background equals in average from 1 up to 2 mSv per year. X-ray imaging for medical use leads in most cases to a radiation dose ranging from 0,2 to 5 mSv. IrradiationInteraction between ionising radiation and environment (including human organism). IsotopeOne of the different "varieties" of a radioactive element. For example, caesium exists as caesium-134 and caesium-137. See also radioactivity.
LiquidatorsChernobyl liquidators are people involved in the elimination of the nuclear disaster’s consequences on site. Among them are clean up workers, construction workers, drivers, soldiers, radiological survey staff, scientists and officials.
Man-caused radiation backgroundRadiation background, which is caused by human (technical) sources – nuclear power plants, medical and other equipment, and global nuclear fall-outs after nuclear weapon tests. Medical procedures contribute approximately 30% of the average radiation dose per person in industrial countries, while nuclear power and global fall-outs contribute about 1%.
Natural ionising radiation backgroundAn integral environmental factor, given the chemical structure of the earth and the cosmic energy. The natural ionising radiation background is created by cosmic rays, the radioactivity of water, air, plants and animals. In average, the individual dose received by the natural radiation background equals approximately from 1 up to 2 mSv per year, of which the biggest part (almost 2/3) is caused by radon, a naturally radioactive gas, always present in rocks, above all in granite.
Nuclear energy (= atomic energy)The energy liberated by a nuclear reaction (fission or fusion) or by radioactive decay.Nuclear fuel cycleAll the processes involved in providing fuel for nuclear energy and disposing of it. This includes the extraction and preparation of nuclear fuel, the manufacture of fuel rods, the reprocessing of spent fuel rods and the final disposal of radioactive wastes. Nuclear powerPower engineering branch, where nuclear power is used for electrification and heating systems.
PlutoniumA heavy, radioactive, man-made metallic element with atomic number 94. Its most important isotope is fissile plutonium-239, which is produced by neutron irradiation of uranium-238. It exists in only trace amounts in nature but was released into the environment following the nuclear accident at Chernobyl. Some of the isotopes of plutonium have a half-life of up to 24 000 years.Pressurized-Water Reactor (PWR)A nuclear reactor in which heat from the core is absorbed by coolant water, which is pressurised (160 bar) to prevent it from boiling. The heated water (around 325°C) is then used to produce steam to drive a turbine. About two thirds of the nuclear power plants in operation worldwide are PWRs.
RadTraditional measure unit for an absorbed radiation dose. 1 rad = 0.01 Gy. Radiation and radioactivityEmission of radiation caused by the disintegration of unstable atomic nuclei. This radioactive decay creates another element, which is often itself radioactive. The decay series (see half-life) continues until a stable (no longer radioactive) element is reached. This is why there are different «varieties» (see isotopes) of each radioactive chemical element. The names of radioactive substances are often given as follows: the chemical symbol for caesium (Cs) is followed by the atomic mass: Cs-137. Isotopes are often also called radionuclides.
Numerous radioactive substances exist in nature (see background radiation). In reactors and laboratories, atomic fission produces artificial radionuclides such as caesium, iodine, strontium and plutonium. These differ in the length of their half-life and the type of radiation (alpha, beta or gamma rays) they emit. The nuclear accident at Chernobyl primarily released caesium-137, iodine-131, uranium-235 and strontium-90 into the environment. Radiation riskProbability of radiation effects occurrence. There are deterministic and stochastic consequences as well as somatic and genetic radiation consequences. Radioactive contaminationPresence of radioactivity on the surface, in the material, in the air or an other place, in a quantity exceeding the levels established. Radioactivity measure unitsThe most commonly used measure units for the radioactivity of soil and food are Becquerel (Bq) and Curie (Ci).
Usually the activity is given for 1 kg of food. Such an activity is called specific. On maps the activity is indicated per unit of area, for example, km2. Caesium 137 is the most common long-life (the half-value period is 30 years) radioactive element on polluted areas after an accident. Therefore, the maps and the contamination levels mean in the most cases pollution by caesium 137. The area contamination level of 1 Ci/km2 itself does not say anything about to what irradiation the people living on that territory were subject to. The measure for a damaging effect of a radiation on humans is the radiation dose, which is measured in Sieverts (Sv).
The corresponding institutions for overcoming the consequences of the catastrophe on the Chernobyl NPP in three affected states base their evaluation on an average effective dose from 0.5 to 1 mSv per year for the inhabitants of areas with a contamination level from 1 to 5 Ci/km2. In the EU states 1mSv is considered as the maximum permissible dose per year for inhabitants in the neighbourhood of a nuclear power plant. RadionuclideSee radiation and radioactivityReactorInstallation used to initiate, maintain and control a fission (or in other cases fusion) chain reaction. Its main components are the core, containing fissionable fuel, the coolant and moderator, control rods, and shielding.RemTraditional system unit for measuring the effective and equivalent dose. 1 rem = 0,01 Sv. Roentgen equivalent man. RiskProbability for the occurrence of negative events.
Safety measuresMeasures used for the protection from ionising radiation. SievertEffective and equivalent measure unit for the radiation dose in the Si-system. The most often used partite unit of Sievert is its thousandth: millisievert. 1 Sievert (Sv) = 1000 millisieverts (mSv). Somatic effectsDamage caused by radiation to the human or animal exposed, as opposed to genetic effects (affecting the germ cells), which may be passed on to future generations.Somatic radiation effectsDirect radiation effects on humans or animals, exposed to radiation. SorbentsSubstances, which can absorb radionuclides and other contaminants. Specific (concentration) activityRelation of the radionuclide activity in a substance to the substance mass (volume). The specific activity unit is Becquerel per kilogram, Bq/kg. The activity concentration unit is Becquerel per cubic meter, Bq/m3. Used to characterise the radioactive contamination of food, water, feed, etc.
Stochastic radiation effectsHarmful biological effects, caused by ionising radiation, which do not have a dose threshold, whose probability is proportional to the dose and for which the seriousness in their manifestation does not depend on the dose. To the stochastic (probabilistic) effects without threshold belong in particular malicious tumours, leucosis, and heritable diseases. StrontiumOne of the radioactive elements released into the environment following the nuclear accident at Chernobyl. Some of the isotopes of strontium have a half-life of up to 90 years.Surface activityCorrelation of the surface radionuclide activity to the surface. Used to characterise the radioactive contamination of a territory (the radioactive pollution density). Unit: Becquerel per square meter, Bq/m2.
The most widely used traditional system unit for the radioactive pollution density is curie per square kilometre, Ci/km2. 1 Ci/km2 = 37 kBq/m2. By this unit the radioactive pollution density of a territory is measured, e.g. Cs-137.
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