Forschungszentrum Karlsruhe Technik und Umwelt GLOSSARY OF NUCLEAR TERMS Winfried Koelzer © Forschungszentrum Karlsruhe GmbH, Karlsruhe, April 2001 Postfach 3640 · 76021 Karlsruhe, Germany Original title: Lexikon zur Kernenergie, ISBN 3-923704-32-1 Translation by Informationskreis KernEnergie The reproduction of trade names, identifications, etc. in this glossary does not justify the assumption that such names may be considered free in the sense- of the laws regulating the protection of trade marks and brands and that therefore they may be used by everyone. No guarantee is given for the correctness of numerical data. Pictures by: Argonne National Lab., Argonne Aulis-Verlag Deubner & Co., Cologne Forschungszentrum Karlsruhe, Karlsruhe Informationskreis Kernenergie, Bonn A Absorbed dose The absorbed dose D is the quotient of the average energy transferred to the matter in a volume element by ionizing radiation and the mass of the matter in this volume element: _ d ε D = . dm The unit of the absorbed dose is joule divided by kilogram (J·kg-1) and its special unit name is gray (Gy). The former unit name was rad (symbol: rd or rad).1 Gy = 100 rd; 1 rd = 1/100 Gy. Absorbed dose rate Quotient of absorbed dose per unit of time. Unit: Gy/h. Absorber Any material "stopping" ionizing radiation. Alpha radiation can already be totally absorbed by a sheet of paper; beta radiation is absorbed by a few centimetres of plastic material or 1 cm of aluminium. Materials with a high →atomic number and high density are used for gamma radiation absorbers (lead, steel, concrete, partially with special additions). Neutron absorbers such as boron, hafnium and cadmium are used in control rods for reactors. Absorber rod →control rod Accelerator Device to accelerate electrically charged particles to high energies. Accelerators include e.g.: →betatron, →linear accelerator, →synchrotron, →synchro-cyclotron, →Van de Graaff generator and →cyclotron. Accident Sequence of events which may result in an effective dose of more than 50 millisievert for at least one person. Accounting Most important method of →nuclear material control in a nuclear facility. Its goal is the quantitative determination of the nuclear material to detect inventory deficiencies (unauthorised diversions). The accounting relates to a defined, limited, walled-in space the contents of which results from the difference of all continuously measured nuclear material additions and withdrawals. At the end of the accounting period the plant inventory is determined by an independent direct measurement. →MUF Activation Process to make a material radioactive by bombardment with neutrons, protons or other particles. 1 Activation of iron Activation analysis Procedure for the quantitative and qualitative determination of chemical elements in a sample to be analysed. The sample becomes radioactive through bombardment with neutrons or charged particles. The resulting radioactive atoms of the sample emit characteristic rays by which the type of atoms can be identified and the quantity measured. The activation analysis is frequently more sensitive than a chemical analysis and is used increasingly in research, industry, archaeology and criminology. Activation cross section Measure of the probability of the occurrence of a reaction. The cross section is the apparent surface which a target nucleus exposes to an arriving particle. The cross section is indicated in surface units. Neutron cross sections are frequently measured in the unit of barn, symbol: b. 1 barn is equal to 10-28 m2. Active beam The bundle of rays emitted by a radiation source, e.g. an x-ray tube. Normally, it is limited to the required size by a diaphragm arrangement. Activity Activity is the term used to characterise the number of nuclei which disintegrate in a radioactive substance per unit time usually measured in Becquerels (Bq); a Bq is 1 disintegration per second. Replaces the former unit →curie, symbol: Ci. 1 Ci is equal to 37 000 000 000 Bq. Note: "Activity" is a quantitative term whereas 'radioactivity' is a qualitative term used to describe atoms that decay. Activity concentration 3 Quotient of the activity 'A' of a material and the volume 'V' of this material, Aconc = A / V. Unit: Bq/m . Activity intake The quantity of radioactive substances inhaled or ingested through mouth or nose or which penetrates the intact or injured skin. Activity, specific Quotient of the activity 'A' of a material and the mass 'm' of this material, Asp = A / m. Unit: Bq/kg. After-power Thermal power of a reactor resulting from the →residual heat in the shut-down reactor. 2 AGR Advanced Gas-Cooled Reactor. A total of 14 reactor units of this type are in operation in England and Scotland. AGR reactors use enriched uranium as fuel, graphite as moderator and CO2 as cooling gas. Air lift Process-based transport and dosing equipment where air is used as a carrier for liquids, e.g. to transport highly active liquids. An air lift has no moving parts and requires twice to five times as much carrier air volume as the transported liquid volume. ALARA Acronym for As Low As Reasonably Achievable. Concept of the International Commission on Radiological Protection for dose limitation, described in detail and substantiated in the recommendation of the International Commission on Radiological Protection of 1990, published in 1991 as →ICRP Publication 60. ALI Annual Limit on Intake →annual limit on intake Alpha decay Radioactive conversion emitting an alpha particle. During alpha decay the →atomic number is reduced by two units and the →mass number by four units. For example, alpha decay generates Rn-222 with the atomic number 86 and the mass number 222 from Ra-226 with the atomic number 88 and the mass number 226. Alpha decay; the figure shows the decay of radium-226 into radon-222 emitting helium with 4 nucleons (2 protons and 2 neutrons = 1 alpha particle, α-particle) Alpha particle Positively charged particle emitted by various radioactive materials during decay. It consists of two neutrons and two protons, and is thus identical to the nucleus of a helium atom. The rest mass of the alpha particle amounts to 6.64424·10-27 kg, or 3.7273·109 eV. Alpha radiation is the radiation with the lowest penetration potential of the three radiation types (alpha, →beta, →gamma radiation). Alpha radiation can already be stopped by a sheet of paper and is only dangerous for living creatures if the substance emitting alpha rays is inhaled or ingested with food or enters wounds. 3 Ambient dose equivalent The ambient dose equivalent H*(10) at the point of interest in the actual radiation field is the dose equivalent which would be generated in the associated oriented and expanded radiation field at a depth of 10 mm on the radius of the ICRU sphere which is oriented opposite to the direction of incident radiation. An oriented and expanded radiation field is an idealized radiation field which is expanded and in which the radiation is additionally oriented in one direction. Schematic representation of an oriented and expanded radiation field Amplitude analysis Process to obtain the energy spectrum of a radiation. The pulses of a detector supplying output pulses proportional to energy are sorted and counted according to their amplitude. The energy spectrum can be derived from the pulse amplitude distribution obtained in this way. Amplitude analyzer Device taking advantage of amplitude analysis to represent the energy spectrum of a radiation. Annihilation radiation Upon the collision of a particle and an anti-particle, e.g. electron and positron, these are „annihilated“ as particles and the mass of these particles converted into energy. Electron and positron have a rest mass which is together equal to an energy of 1.02 MeV. Upon the „annihilation“ of both particles, two gamma quanta of 0.511 MeV each are generated. Occurrence of annihilation radiation upon collision of electron and positron. Two gamma quanta of 0.511 MeV each result. Annual limit on intake (ALI) 4 The intake in the body by inhalation, ingestion or through the skin of a given radionuclide in a year which would result in a committed dose equal to the relevant dose limit. Annular gap Clearance between the two parts of a double containment kept under negative pressure. In the case of leaks in the inner containment, radioactive substances entering the annular gap are aspirate d and either repumped or filtered and discharged via the vent stack in a controlled way. Anticoincidence circuit Electronic circuit which only supplies an output pulse when a pulse occurs at one - mostly predetermined - input. No output pulse is sent if pulses occur simultaneously at other inputs or are delayed by a certain period. Antimatter Matter in which the core particles (neutrons, protons, electrons) are replaced by the corresponding antiparticles (antineutrons, antiprotons, positrons). Antiparticles Antiparticles have the same mass, the same average life and the same spin as the corresponding particles, but opposite and equal baryon and lepton numbers. Antiparticles and particles are either both electrically neutral or they have an equal electric charge, but opposite signs. Particle: Proton Antiparticle:Antiproton Mass 1.6726·10-27 kg 1.6726·10-27 kg Average life time Stable Stable Spin 1/2 ħ 1/2 ħ Baryon number +1 -1 Lepton number 0 0 Electric charge +1.6022·10-19 C -1.6022·10-19 C Key data for the proton/antiproton particle/antiparticle pair APP Atomic power plant, →nuclear power plant Argonaut Argonne Nuclear Assembly for University Training; type of training reactor. ASME American Society of Mechanical Engineers, New York, N.Y., USA. Asse Former rock-salt mine 10 km to the south-east of Wolfenbüttel built for the trial ultimate waste disposal of low and medium active waste. More than 120 000 barrels equal to around 24 000 m3 of low active waste have been stored here.