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Activation product
Neutron activation products are radioactive substances formed from the elements in ordinary materials - such as steel and concrete and air - when these elements absorb neutrons generated in fission or fusion reactions in a nuclear explosion.
Alpha particle
The positively charged particle from the nucleus of an atom emitted during radioactive decay. Alpha particles are helium nuclei, with 2 protons and 2 neutrons. To trigger a nuclear explosion, alpha particles are used to change beryllium-9 to beryllium-8 and free neutrons. The neutrons then initiate fission.
Atmospheric test
From 1945 to 1963 the United States conducted atmospheric nuclear tests -- that is nuclear explosions above ground, usually with the device placed on a tower or dropped from a plane -- grouped into roughly 20 test "series." After 1963 when the Limited Test Ban Treaty was signed, testing by the United States, Soviet Union and Britain moved underground. France continued atmospheric testing until 1974 and China did so until 1980.
Atom
A particle of matter that cannot be broken down by chemical means. Atoms have a nucleus consisting of positively charged protons and uncharged neutrons of the same mass. The positive charges on the protons are balanced by the same number of negatively charged electrons in motion around the nucleus.
Atomic Bomb - See Types of Nuclear Bombs
Background radiation
Naturally occurring ionizing radiation from the sun and other sources.
Ballistic missile
A missile that travels to its target unpowered and unguided after being launched and at a velocity such that it will follow a flight trajectory to a desired point. Part of the flight of longer-range ballistic missiles may occur outside the atmosphere and involve the "reentry" of the missile. Additionally, ballistic missiles can be designed to reach several thousand miles. These missiles are commonly called Intercontinental Ballistic Missiles, or ICBMs.
Becquerel
The internationally recognized unit of radioactivity in a material. One Bq measures one disintegration per second, so it also measures one decay per second in a radioactive material. (In practice, GBq or TBq are the common units.)
Beta particle
A particle emitted from an atom during a nuclear explosion. Beta particles may be either electrons or positrons and can cause harm to humans, but can be stopped by a light barrier such as 6 millimeters of aluminum.
Biological shield
A mass of absorbing material, such as thick concrete walls, placed around a reactor or radioactive material to reduce the radiation.
Chain reaction
A reaction that stimulates its own repetition, in particular where the neutrons originating from nuclear fission cause an ongoing series of fission reactions.
Control rods
Devices to absorb neutrons so that the chain reaction in a reactor's core may be slowed or stopped by inserting them further, or accelerated by withdrawing them.
Conventional weapon
The U.S. government divides weapons into conventional weapons: guns, landmines, artillery, etc., and unconventional weapons: which can mean weapons of mass destruction such as chemical, biological or nuclear bombs, but also terrorist weapons.
Core
The central part of a nuclear reactor containing the fuel elements and any moderator.
Critical
Critical mass is the minimum mass of fissionable material required to sustain a nuclear fission reaction. A nuclear reaction "goes critical" when the U-235 nuclei begin to split. Then the mass of the uranium is considered to be critical.
Cruise missile
An unmanned self-propelled guided vehicle that sustains flight through aerodynamic lift for most of its flight path. A cruise missile may deliver a conventional or nuclear warhead.
Depleted uranium
Uranium having less than the natural 0.7 percent U-235. As a by-product of enrichment in the fuel cycle it generally has 0.25-0.30 percent U-235, the rest being U-238. Can be blended with highly enriched uranium (e.g. from weapons) to make reactor fuel.
Deterrence
A concept that came out of the arms race of the 1940s and '50s that nuclear weapons should serve the purpose to prevent their use. Nuclear deterrence is the threat to retaliate with nuclear weapons.
Deuterium
"Heavy hydrogen," a stable isotope having one proton and one neutron in the nucleus. It occurs in nature as 1 atom to 6,500 atoms of normal hydrogen, (Hydrogen atoms contain one proton and no neutrons). Heavy water, D2O, is water in which both hydrogen atoms have been replaced with deuterium. Heavy water is the key to one type of reactor in which plutonium necessary for a bomb can be bred from natural uranium. As such, the production of heavy water has always been monitored, and the material is export controlled.
Dirty Bomb
A dirty bomb is a conventional explosive such as dynamite, filled with radioactive particles which scatter when the bomb goes off. Known as a radiological weapon, a dirty bomb's initial conventional explosion kills or injures people, and then spreads radiation -- hence the term "dirty." Such bombs could be miniature devices or be as big as a truck.
Enriched uranium
Uranium with an increased concentration of the isotope U-235. Natural uranium contains 0.7 percent U-235, whereas nuclear weapons typically require uranium enriched to 90 percent or more U-235. Nuclear power plant fuel typically uses uranium enriched to 3-5 percent U-235, material that is not sufficiently enriched to be used for nuclear weapons.
Enrichment
Physical process of increasing the proportion of U-235 to U-238.
Fissile
Fissile materials have the property that when their atomic nucleus is hit by a stray neutron, the atom will split and release several other neutrons. If the percentage of the fissile isotopes is high enough, a self-sustaining nuclear chain reaction will occur.
Fission
The splitting of a heavy nucleus in two, accompanied by the release of a relatively large amount of energy and usually one or more neutrons. It may be spontaneous but usually is due to a nucleus absorbing a neutron and thus becoming unstable.
Fusion
When two atoms fuse into one larger atom. In fusion bombs, deuterium and tritium -- two isotopes of hydrogen -- are fused together to create heavier atoms. This is the same reaction as occurs in the centre of the sun. Fusion can only happen at very high temperatures and pressures. In a nuclear weapon these are created through using a fission explosion (i.e., an atom bomb) to trigger the fusion reaction.
Gamma ray
High energy, electromagnetic radiation from the atomic nucleus, virtually identical to X-rays. Gamma rays are the first energy to escape from a nuclear explosion. They are the hardest to stop with shielding. They can travel through hundreds of feet of air and the walls of ordinary houses, delivering deadly radiation doses.
Gray
The international unit of absorbed radiation dose, one joule per kilogram of tissue.
Heavy water
Water containing an elevated concentration of molecules with deuterium ("heavy hydrogen") atoms. The neutron in the deuterium nucleus allows this type of water to slow, or moderate, neutrons from fissioning uranium, permitting a sustained chain-reaction in reactors using natural uranium as fuel.
Highly enriched uranium (HEU)
Uranium enriched to at least 20 percent U-235. (HEU for weapons use is usually about 90 percent U-235.)
Hydrogen bomb - See Types of Nuclear Bombs
IAEA
Headquartered in Vienna, Austria, the International Atomic Energy Agency calls itself "the world's center of cooperation in the nuclear field." It was set up as the world's "Atoms for Peace" organization in 1957 within the United Nations family. The agency works with its member states and multiple partners worldwide to promote safe, secure and peaceful nuclear technologies.
Ion
An atom that is electrically charged because of loss or gain of electrons.
Ionizing radiation
Radiation (including alpha particles) capable of breaking chemical bonds, thus causing ionization of the matter through which it passes and damage to living tissue.
Irradiate
Subject material to ionizing radiation. Irradiated reactor fuel and components have been subject to neutron irradiation and hence become radioactive themselves.
Isotope
An atomic form of an element having a particular number of neutrons. Different isotopes of an element have the same number of protons but different numbers of neutrons and hence different atomic mass, e.g. U-235, U-238. Some isotopes are unstable and decay to form isotopes of other elements.
Kiloton
A measure of explosive power equal to that of 1,000 tons of TNT.
Light-water reactor
A term used to describe reactors using ordinary water as coolant, including boiling water reactors (BWRs) and pressurized water reactors (PWRs), the most common types used in the United States.
Low-enriched uranium
Uranium enriched to less than 20 percent U-235. (That in power reactors is usually 3.5-5.0 percent U-235.)
MAD (Mutually Assured Destruction)
A military doctrine of deterrence that began to emerge at the end of the Kennedy administration. MAD reflects the idea that the deployment of strong weapons is essential to assure the enemy that any use of nuclear weapons would result in the destruction of both the attacker and the attacked.
Megaton
A measure of explosive power equal to 1 million tons of TNT.
Megawatt (MW)
A unit of power, = 106 watts.
Natural uranium
Uranium with an isotopic composition as found in nature, containing 99.3 percent U-238, 0.7 percent U-235 and a trace of U-234. Can be used as fuel in heavy water-moderated reactors.
Neutron
An uncharged elementary particle found in the nucleus of every atom except hydrogen. Solitary mobile neutrons originate from fission reactions. Slow (thermal) neutrons can in turn readily cause fission in nuclei of "fissile" isotopes, e.g. U-235, Pu-239, U-233; and fast neutrons can cause fission in nuclei of "fertile" isotopes such as U-238, Pu-239.
Nuclear weapon
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Tactical Nuclear Weapon
There is a great deal of debate over the exact definition of a Tactical Nuclear Weapon (TNW). At least seven different factors are used by different authorities to define a tactical weapon: range, yield, intended target, national ownership, capability, delivery vehicle, or exclusion. TNW are called "low-yield," with an explosive force ranging from 0.1 kiloton (100 tons of TNT) to 1.0 megaton (1 million tons of TNT). A "low yield" explosion of 120 KT is equivalent to 120,000 tons of TNT and is almost 10 times the yield of the bomb dropped on Hiroshima. In general, TNW are short-range, covering approximately less than 300 miles; low-yield compared to strategic nuclear weapons; intended for battlefield use in a theater setting; more portable and diverse than strategic bombs. TNW can take the form of artillery shells, nuclear mines, atomic demolition munitions, gravity bombs and missile warheads. They are not currently covered by arms control treaties.
Strategic Nuclear Weapon
Strategic weapons are targeted based on a strategic plan and generally include nuclear missile forces and cities. The definitions of strategic and tactical weapons overlap, but strategic weapons are generally larger with explosive forces over one megaton. Range is also a factor. Intercontinental missiles are considered strategic weapons but short-range missiles such as those deployed in Europe were non-strategic. Accordingly, the intra-continental arsenals of France, India, Pakistan and the U.K. are tactical weapons with strategic roles in nuclear planning. |
Plutonium
An element formed in a nuclear reactor by neutron capture. It has several isotopes, some of which are fissile and some of which undergo spontaneous fission, releasing neutrons. Weapons-grade plutonium is produced in special reactors to give more than 90percent Pu-239, reactor-grade plutonium contains about 30 percent non-fissile isotopes.
Proliferation
The spread of nuclear weapons around the world. Also refers to the spread of nuclear technology and bomb-making materials.
Radiation
The emission of energy in the form of electromagnetic waves or particles.
Reactor
A device that harnesses the energy in a nuclear fission chain reaction. Commercial reactors are thermal reactors, using a moderator such as water to slow down the neutrons.
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Boiling water reactor
A common type of light water reactor where water is allowed to boil in the core thus generating steam energy.
Breeder reactor
Fast breeder reactor (FBR): A fast neutron reactor (qv) configured to produce more fissile material than it consumes, using fertile material such as depleted uranium in a blanket around the core.
Fast neutron reactor
A reactor with little or no moderator and hence utilizing fast neutrons. It normally burns plutonium while producing fissile isotopes in fertile material such as depleted uranium.
Heavy water reactor (HWR)
A reactor that uses heavy water as its moderator.
Light water reactor (LWR)
A common nuclear reactor cooled and usually moderated by ordinary water.
Pressurized water reactor (PWR)
The most common type of light water reactor (LWR), it uses water at very high pressure in a primary circuit and steam is formed in a secondary circuit.
Thermal reactor
A reactor in which the fission chain reaction is sustained primarily by slow neutrons, and hence requiring a moderator (as distinct from Fast Neutron Reactor, which has little to no moderator). |
Reprocessing
Chemical treatment for spent reactor fuel that separates uranium and plutonium from the small quantity of fission product waste products and transuranic elements, leaving a much-reduced quantity of high-level waste.
Sievert (Sv)
Unit indicating the biological damage caused by radiation. One joule of beta or gamma radiation absorbed per kilogram of tissue has 1 Sv of biological effect; 1 J/kg of alpha radiation has 20 Sv effect and 1 J/kg of neutrons has 10 Sv effect.
Silo
The structures, usually underground bunkers, that hold nuclear missiles.
Uranium (U)
A mildly radioactive element with two isotopes which are fissile (U-235 and U-233) and two which are fertile (U-238 and U-234). Uranium is the basic fuel of nuclear energy.
Waste
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High-level waste (HLW)
Highly radioactive material arising from nuclear fission. It can be recovered from reprocessing spent fuel. It requires very careful handling, storage and disposal.
Low-level waste (LLW)
Mildly radioactive material usually disposed of by incineration and burial. |
Yellowcake, Uranium oxide concentrate (U3O8)
The mixture of uranium oxides produced after milling uranium ore from a mine. It is khaki in color.
-- Compiled by Leah Clapman for the Online NewsHour
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