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Glossary of Radiographic Terms

A

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Accelerator

A device that uses electric fields to increase the energy of charged particles, such as electrons and protons, to the point where they can induce a nuclear reaction upon collision with a target material.

Neutron-nuclear absorption reactions involve the absorption of a neutron by a nucleus and the release of energy. Fission is a type of neutron absorption reaction.

A parameter characterizing the probability that a neutron-nuclear absorption reaction will occur.

A series of 15, chemically similar, artificially prepared, radioactive elements ranging from atomic number 89 (actinium) to atomic number 103 (lawrencium).

See ‘Radioactivity’

The process of causing a material to become radioactive.

A material made up of a mixture of two or more metals or metals and non-metals, often increasing the resulting material strength.

An electrically charged particle emitted from the nucleus of an atom, containing two protons and two neutrons, identical to the nucleus of a helium atom, without electrons.
Also see: Beta particle, Gamma rays.

 

A device controlling the amount of light admitted in an optical system.

An indication in an image that is not associated with any defect or other physical characteristic of the specimen.

An approach to radiation protection that aims to manage both individual and collective doses to the work force, the general public and the environment keeping doses as low as social, technical, economic, practical and public policy considerations allow.

Atom

The smallest component of a chemical element having the chemical properties of that element, made up of a nucleus surrounded by electrons; from the Greek word ‘atomos’ meaning indivisible.

Atomic Mass

The mass of an atom, approximately equal to the number of protons plus the number of neutrons located in the atom’s nucleus.

A mass unit equalling 1.66 x 10^-27 kg.

Different for each element, the atomic number is the number of protons in the nucleus of an atom, and is used for element identification.

Atom Smasher

A machine (an accelerator) that speeds up atomic and subatomic particles so that they can be used as projectiles to literally blast apart the nuclei of other atoms.
Also see: Accelerator.

Attenuate

To lessen the amount, force, or value of.

Attenuation

The reduction in the intensity of radioactivity by absorption or scattering while passing through a material. 

Auto Radiography

Self-portraits of radioactive sources made by placing the radioactive material next to photographic film. The radiation fogs the film leaving an image of the source. It was such self-portraits that led to the discovery of radioactivity.

B

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Common unit of microscopic cross section measure. 1 b = 10^-24 cm^2.

Background Radiation

The natural radiation present in everything surrounding us. Examples of this include radiation from the sun's rays, radiation from elements in the ground, and radiation from within our bodies. Background radiation varies with location and time, and it can never be reduced to zero.

 

A small electrically charged particle thrown off by many radioactive materials. It is identical to the electron by originates from an atomic nucleus. A beta particle possesses the smallest electric charge found in nature
Also see: Alpha particle, Gamma ray.

 

A large doughnut-shaped accelerator in which electrons (beta particles) are whirled through a changing magnetic field gaining speed with each trip and emerging with high energies. Energies of the order of 100 million electron volts have been achieved. The Betatron produces artificial beta radiation.

Binding Energy

The energy required to separate a particle (proton, neutron or electron) from an atom or molecule.

The act of subjecting an object or substance to the impact of high-energy particles such as neutrons or beta particles.

The process of transforming a fertile material into a fissile material. Nuclear reactors often breed plutonium-239 from uranium-238.

A reactor that produces more nuclear fuel than it consumes through the process of breeding..

A measure of the thermal energy released by nuclear fuel relative to its mass.

 

C

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The Canadian Nuclear Safety Commission controls the development, application, and use of nuclear energy in Canada.

 

A light-tight device for holding a film-screen combination in close contact during a neutron radiography exposure. Cassettes may encorporate pressure or vacuum to improve film to screen contact.

Cerenkov Radiation

A blue glow emitted by a charged particle when it travels through a medium, faster than the speed of light in that medium. Cerenkov radiation can be seen in some nuclear reactors in the water surrounding the core.

 

A reaction in which reactants necessary to undergo the reaction are produced by the reaction, resulting in a self-sustaining reaction. Neutrons, necessary in order for fission to occur, are produced in a fission reaction, enabling fission to continue with no external input.

Cobalt-60

A radioactive isotope of the element cobalt. Cobalt-60 is an important source of gamma radiation and is used widely in research and medical treatments.

 

A numerical measure of a physical or chemical property that is constant for a system under specified conditions such as the linear attenuation coefficient.

 

A measure of the resolution of a neutron radiography facility. The most common definition is the ratio of the image-to-aperture distance to the aperture diameter. Also called L/D (‘L’ over ‘D’).

A device for producing a beam of parallel rays of light or other radiation or for forming an infinitely distant virtual image that can be viewed without parallax.  2:  a device for obtaining a beam of molecules, atoms, or nuclear particles of limited cross section.

 

A type of gamma interaction with a material where the photon collides with an electron, resulting in an increase in electron energy and a decrease in photon energy.

 

Radioactive substances dispersed in materials and places where it is undesirable. An object is contaminated when radioactive particles attach themselves to non-radioactive materials. Exposure to radiation does not contaminate a material.

 

A rod used to control the power of a nuclear reactor. The reactor functions through the splitting of nuclear fuel atoms by interaction with neutrons. The control rod absorbs neutrons, which would normally split atoms of the fuel. Pushing the rods in reduces the release of atomic energy. Pulling the rods out increases the release of atomic energy.

 

A reactor that uses one kind of fuel and produces another. For example a converter charged with uranium isotopes might consume uranium-235 and produce plutonium from uranium-238.

 

A fluid that circulates through the reactor removing fission heat.

 

The part of a nuclear reactor where the fission reaction occurs, the fuel location. The total array of fuel, moderator and control elements.

Cosmotron

A huge accelerator, one of the atomic "guns," located at Brookhaven National Laboratory. It speeds up particles to the billion electron volt range. The Brookhaven machine has a magnet weighing 2,200 tons.

 

A device for counting nuclear disintegrations to measure radioactivity. The signal which announces a disintegration is called a count.

 
 

A mass of fissile material is critical if it is capable of a sustained chain reaction. Criticality depends on the material size, shape, purity and surroundings

 

An assembly of nuclear materials capable of achieving criticality.

 

The amount of nuclear fuel in the proper shape necessary to sustain a chain reaction. If too little fuel is present, or the mass is not in the proper shape, too many neutrons will stray and the reaction will die out.

 

A reaction is said to have achieved criticality if it is generating enough neutrons to maintain the reaction at the same level that it is currently operating at. Creating too many neutrons makes the reaction super-critical, and too few neutrons makes the reaction sub-critical.
See also: Sub-Critical, Super-critical.

 

The nuclear cross section is a parameter characterizing the probability that a neutron-nuclear reaction will occur.

The traditional unit of measure for radioactivity. The radioactivity of one gram of radium is a Curie. The Curie was named for Pierre and Marie Curie, pioneers in radioactivity and discoverers of the elements radium, radon, and polonium.

 

A circular particle accelerator in which the particle path is bent in traveling through a magnetic field. An oscillating potential difference causes the particles to gain energy.

 

D

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The process by which the nucleus of a radioactive isotope decomposes and releases radioactivity. For example, carbon 14 (a radioisotope of carbon) decays by losing a beta particle, thereby becoming nitrogen 14, which is unstable.

 

One or more flaws whose aggregate size, shape, orientation, location or properties do not meet specified acceptance criteria and are rejectable.

Delamination

The separation of a laminated plastic material along the plane of its constituent layers.

Accidents that are postulated for the purpose of establishing requirements for safety of significant structures, systems, components, and equipment.

 

An isotope of hydrogen containing one neutron and one proton in its nucleus, therefore weighing twice as much as a hydrogen atom.

 

The nucleus of an atom of deuterium.

 

A drawing apart.  2. deviation from a course or standard.

 

Neutron radiography carried out with the imaging medium in the neutron beam with the object.

 

A lack of continuity or cohesion; an intentional or unintentional interruption in the physical structure or configuration of a material or component.

Dose  

The quantity of radiation energy absorbed by a tissue or person while the tissue or person is present in a radiation field.

 

An instrument used in measuring the radiation dose a person has received.

E

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A method to treat or stabilize spent nuclear fuel for ultimate disposal.

Effective Dose

For a person, the effective dose is the sum of equivalent doses to each organ or tissue multiplied by a tissue weighting factor. Equal effective doses to different tissues or organs produce the same detriment. The tissue weighting factor adjusts for the varying sensitivity of tissues and organs to radiation exposure. The SI unit of equivalent dose is the sievert (Sv) and the traditional unit is the rem.

Net electrical power generated, measured in ‘megawatts electric’, MWe.

Electro-mechanical Manipulators

Electro-mechanical manipulators serve a function similar to that of master-slave manipulators, but are power operated. Large contaminated or radioactive objects cannot be handled or examined without mechanical assistance. Cranes and motor driven manipulators allow engineers full freedom to work safely with spent fuel or any other health hazardous materials.

 

A minute atomic particle possessing the smallest amount of negative charge found in nature. In an atom the electrons rotate around a small, massive nucleus. The weight of an electron is so small that it would take 500 octillions (followed by 27 zeros) of them to make a pound. The mass of an electron is approximately one two-thousandth of the mass of a proton or neutron
See also: Proton, Neutron.

 

A small unit of energy used for expressing the energy of nuclear processes on the atomic level. Also expressed in kilo electron-volts (keV) and mega electron-volts (MeV).

 

A basic substance consisting of a "family" of naturally occurring isotopes. For example, hydrogen, lead, and oxygen are elements. All atoms of an element contain a definite number of protons and thus have the same atomic number.

 

Made better or improved in quality. Natural uranium contains about 0.7% U-235. For use in reactors, it is usually enriched so that it contains a higher percentage of U-235.

Epithermal Radiography

The use of neutrons of energy greater than ~ 0.5 eV (greater than thermal) for radiographic inspection.

Equivalent Dose

The average absorbed dose for a tissue or organ multiplied by the radiation weighting factor. The SI unit of equivalent dose is the sievert (Sv) and the traditional unit is the rem.

Evaluation

A review, following interpretation of the indications noted, to determine whether they meet specified acceptance criteria.

The operation of a reactor beyond its normal operating limits. This is usually done experimentally to test reactor stability and to explore safety features of nuclear reactors.

 

F

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An indication that is interpreted to be caused by a condition other than a discontinuity or imperfection.

Fast Neutron

Neutrons having energy levels greater than 0.1 MeV. Neutrons ejected from a nucleus during fission that have not been slowed by a moderator are fast neutrons.

 

A nuclear reactor that operates using fast neutrons.

Fertile

Isotopes that can be transmitted into fissile nuclides via neutron capture. Examples of fertile nuclei include U-238 and Th-232.

 

A piece of masked photographic film worn like a badge by nuclear workers. It is darkened by nuclear radiation, and radiation exposure can be checked by inspecting the film.

 

The splitting of a nucleus into at least two other nuclei, releasing a relatively large amount of energy. On average, two to three fast neutrons are released during a fission reaction. Fission reactions are induced by thermal neutrons and occur only with heavy elements such as uranium and plutonium.

 

Nuclides that can be induced to fission with neutrons of energy greater than thermal neutrons. Fissile nuclides, Th-232 and U-238 are examples of fissionable nuclei.

 

Nuclides that can be induced to fission with thermal neutrons having very small kinetic energies. U-235 and Pu-239 are examples of fissile nuclei.

The nuclei formed by the fission of heavy elements. They are of medium atomic weight and often radioactive. Fission products include a wide range of common elements such as iodine, cesium, and strontium.

 

An imperfection or discontinuity that may be detectable by nondestructive testing and is not necessarily rejectable.

The process of quantifying the size, shape, orientation, location, growth, or other properties of a flaw based on NDT response. 

The number of items passing through a unit area in a unit time. Neutron flux is measured in units of neutrons/cm2/s.

 

A thin, flexible metallic sheet. Some foils, used in neutron radiography are capable of absorbing neutrons, causing the emission of energy.

Fuel

Any fissionable material such as U-235, U-238, P-239 and Th-232. Most reactors utilize this fuel in a ceramic form.

The smallest unit combining fuel elements into an assembly. A fuel bundle is made up of several fuel elements.

Fuel cladding is a metal used to encase nuclear fuel for the purposes of protection and structural support. Zirconium alloys are often used for cladding material.

Fuel Element

The smallest sealed unit of fuel. A fuel element, also called a fuel rod, is often a metal tube containing ceramic pellets of fuel.

The joining of atomic nuclei to form a heavier nucleus, accomplished under conditions of extreme heat (millions of degrees). If two nuclei of light atoms fuse, the fusion is accompanied by the release of a great deal of energy. The energy of the sun is believed to be derived from the fusion of hydrogen atoms to form helium.

G

A form of highly biologically penetrating ionizing radiation, gamma rays are the highest energy, shortest wavelength electromagnetic radiation. Gamma rays are commonly thought of as any photon having energies greater than 100 keV.

 

A gas-filled electrical device which detects the presence of radioactivity by counting the formation of ions.

 

A form of carbon used as 'lead' in pencils, as well as a highly effective neutron moderator.

Gray

The SI unit of absorbed dose, equal to one joule of energy deposition per kilogram.

 

H

A means of classifying the rate of decay of radioisotopes according to the time it takes for half of the atoms of a sample to decay. Half lives range from fractions of seconds to billions of years. Cobalt-60, for example, has a half-life of 5.3 years.

Half-Value Layer

The amount of material required to reduce the intensity of a radiation field to half of its original intensity.

A method of transferring heat from one fluid to another without the actual contact of those fluids.

  

Water containing deuterium atoms instead of regular hydrogen atoms. Heavy water is widely used in nuclear reactors as a neutron moderator.


A common term used to describe the state of being radioactive.

 

A hot cell is a heavily shielded room that allows engineers to examine highly radioactive or contaminated materials. The walls are made from special materials that will not allow the harmful radiation to escape.
See also: Shielded cells.


Made up of, or containing hydrogen. Water, plastics, rubber and wax are all hydrogenous materials.

 

I

To subject to electromagnetic radiation.

Imperfection

A departure of a quality characteristic from its intended condition.
 

The use of safety systems that need no computer or human response to function. Systems that are inherently safe depend on natural phenomena and the laws of physics to operate.

Ion

An atom or molecular fragment that has a positive or negative electrical charge due to the loss or acquisition of one or more electrons, respectively.

 

A device roughly similar to a Geiger counter and used to measure radioactivity.

 

Having been exposed to radiation, not necessarily radioactive.

 

An atom having the same number of protons in its nucleus as other varieties of the element but a different number of neutrons. Isotopes have the same atomic number but different masses. U-235 and U-238 are both isotopes of Uranium..

 

The change or decomposition of one isotope into another isotope.

J

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The derived SI unit of energy, equal to one Newton-metre.

K

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L

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Lay-up

The act of putting the nuclear reactor facility in the state of protective storage.

 

In radiation physics, the fraction of a beam of radiation that is absorbed or scattered per unit thickness of absorbing material.

 

Waste that contains radioactivity and is not classified as high-level waste, transuranic waste, spent nuclear fuel, or by-product material.

 

A reactor that is designed to produce relatively small amounts of energy. Reactors of this type are primarily used for research or testing.

M

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The cross section characterizing the probability of interaction of a neutron with a unit thickness of a specific material, a macroscopic size scale.

Master Slave Manipulators

Mechanical hands used to handle hot materials. They are remotely controlled from behind a protective shield.

Metallurgy

The science and technology of metals.

 

The cross section characterizing the probability of interaction of a neutron with only a single nucleus, a microscopic size scale.

 

A material used for the purpose of reducing neutron energy. Moderation of fast neutrons to thermal neutrons is essential in acquiring a nuclear chain reaction. Materials containing atoms closest in mass to that of a neutron are the most effective moderators, such as hydrogen and carbon.

 

A collection of two or more atoms held together by chemical bonds; the smallest unit of a compound that displays the properties of the compound.

 
 

N

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Sub-atomic particle with no charge located in the nucleus of an atom having mass slightly greater than that of a proton.
See also: Electron, Proton.

 

A non-destructive testing technique whereby and object is bombarded with neutrons in order to produce an image of its internal structure. A neutron radiograph is similar to an X-ray image, but displays different properties of materials.

 

Inspection methods involving no alteration of physical state or rearrangement of chemical constitution.

 

An indication that is caused by a condition or type of discontinuity that is not rejectable. False indications are non-relevant.

 

Shooting atomic projectiles at nuclei, usually in an attempt to split the target atom or to form a new element.

 

Energy released in a nuclear reaction such as fission (splitting of an atomic nucleus) or fusion (joining of two atomic nuclei).

Nuclear Excursion

The rapid release of reactor power above set operation levels.

A process that alters the energy, structure or composition of atomic nuclei. Examples of nuclear reactions include fission, fusion and radioactive decay.

 

The massive, positively charged central part of an atom, composed mainly of protons and neutrons, around which the electrons revolve.

Nuclear Safety and Control Act

Canadian federal legislation governing all uses of radioactivity in Canada.

 

O

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P

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A type of gamma interaction with material. A high-energy photon (> 1.022 MeV) moves in close proximity to an atomic nucleus and an electron-positron pair is spontaneously generated.

Photoelectric Effect

The emission of an electron from a surface as the surface absorbs a photon of electromagnetic radiation. Electrons so emitted are termed photoelectrons.

Photon

A quantum or distinct bundle of electromagnetic energy.

 

Term for a nuclear reactor derived from the fact that early reactors were "piles" of graphite blocks and uranium slugs.

 

An ore containing both uranium and radium. The Curies had to purify tons of pitchblende to obtain a barely visible speck of radium.

 

An artificially prepared element, isotopes of which are fissile.

 

A substance that reduces the number of fission reactions occurring by absorbing neutrons. The presence of high enough poison levels in a nuclear reactor core will cause the chain reaction to stop.

  

A particle having the same mass and charge as an electron but being electrically positive rather than negative. The positron's existence was predicted in theory years before it was actually detected. Positrons are not stable in matter as they recombine with free electrons in the process of annihilation.

 

A proton is a subatomic particle found in the nucleus of every atom. The proton has a positive electrical charge, equal and opposite to that of the electron. If isolated, a single proton would have a mass of only 1.673 x 10-27 kilogram, just slightly less than the mass of a neutron.
See also: Electron, Neutron.

Q

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R

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Radial

Pertaining to the radius or line from a circle centre to the circumference of the circle. A type of neutron beam.

 

Energy traveling as a wave motion, i.e. the energy of electromagnetic waves.

 

The rate of flow of radiant energy.

 

Energy that is transmitted in the form of rays, waves or particles. Major forms of radiation include alpha, beta, gamma, and neutron radiation.

 

Material for which there is no longer a useful purpose and contains radioactive materials, thus requiring special procedures for management, storage and disposal.

 

The spontaneous decay or disintegration of an unstable atomic nucleus accompanied by the emission of radiation.

 

An image produced on a sensitive surface by a form of radiation other than light.

 

The art, act, or process of making radiographs.

 

A radioactive isotope of an element. Radioisotopes can be produced by placing material in a nuclear reactor and bombarding it with neutrons. Radioisotopes are used as tracers in many areas of science, industry and medicine.

 

Direct observation of objects opaque to light by means of some other form of radiant energy.

 

A radioactive decay product of uranium often found in uranium ore. Radium has several radioactive isotopes.

 

A vessel containing a nuclear reaction. In a reactor, fission of a nuclear fuel releases energy in the form of heat, which is absorbed by water. The energy causes the water to change state into steam, which can be used to drive turbines connected to generators, producing electricity.

Relevant Indication

An indication that is caused by a condition or type of discontinuity that requires evaluation.

The process or capability of making distinguishable the individual parts of an object, closely adjacent optical images or sources of light.

 

The traditional unit of measure of exposure to ionizing radiation.

 

S

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A neutron-nucleus scattering interaction occurs when a neutron collides with the nucleus of an atom and is randomly deflected at a lower energy. Neutron scattering can be elastic or inelastic.

A parameter characterizing the probability that a neutron-nuclear scattering reaction will occur.

Scram

To shut down a nuclear reaction by inserting control rods or some other sort of poison. The term is derived from the acronym for Safety Control Rod Axe Man. During the first reactor experiments, the control rods to stop the reaction were suspended by a rope. The safety control rod axe man stood by the rope to cut it with an axe in case of an accident. Once the rope was cut, the rods fell into the core, and the reaction stopped.

 

Absorbing material used to attenuate both neutron and gamma radiation.

 

A place where radioactive materials can be stored or worked with safely. The shielding can be formed from many materials: lead, thick concrete, steel, dirt, etc.

Seivert (Sv)

The SI unit of effective and equivalent dose, equal to one Joule per kilogram.

 Slug

A "fuel element" for a nuclear reactor, a piece of fissionable material. The slugs in large reactors consist of uranium metal coated with aluminum to prevent corrosion.

 

Any substance which emits radiation. Usually refers to a piece of radioactive material conveniently packaged for scientific or industrial use.

 

An instrument used in separating incoming radiation into its constituent wavelengths or energies.

Spent Nuclear Fuel

Used nuclear reactor fuel composed of fissile material that has reached the end of its usefulness as a result of reactor operation.

Sub-Critical

A state in which a fissionable mass is not critical or super-critical. When a mass is sub-critical, the number of free neutrons that escape the core is greater than the number of free neutrons being generated. If the core of a nuclear reaction becomes sub-critical, the reaction will not be able to sustain itself and it will die out.

 

A state in which a fissionable mass is above the criticality point. When a mass is super-critical, the number of free neutrons that escape the core is less than the number of free neutrons being generated by fission. If the core of a nuclear reaction becomes super-critical, the power of the reaction will grow exponentially until stopped either by natural processes, such as thermal expansion, or by operator action.

 

The act of heating a material, such as water (steam), well above its boiling point. In some reactors, steam is superheated to a temperature of 850F to allow it to turn turbines with greater efficiency.

T

A direction along the tangent of a circle; following a straight line perpendicular to the radius. A type of neutron beam.

 

A neutron having energy in the range 0.01 eV to 0.3 eV, with a nominal value of 0.025 eV, which corresponds to a speed of 2200 m/s. Thermal neutrons are significantly more likely to interact with the nucleus of an atom resulting in fission than are fast neutrons. Neutrons released in a fission reaction are born at high energies and must therefore be slowed using a moderator in order to maintain criticality..

Thermal Power

Power produced in the form of heat, measured in ‘megawatts thermal’, MWt.

 

A fusion reaction, that is, a reaction in which two light nuclei combine to form a heavier atom, releasing a large amount of energy. This is believed to be the sun's source of energy. It is called thermonuclear because it occurs only at a very high temperature.

 

A heavy element. When bombarded with neutrons, thorium changes into uranium, becoming fissionable and thus a source of atomic energy.

 

A diagnostic technique using radiographs in which the shadows of structures in front of and behind the section or plane under scrutiny do not show. 

A radioisotope mixed with a stable material, which enables people to trace the material as it undergoes chemical and physical changes. Tracers are used widely in science, industry, and agriculture. When radioactive phosphorous, for example, is mixed with a chemical fertilizer the radioactive substance can be traced through the plant as it grows.

Transfer Radiography

Neutron radiography where the imaging medium, usually film, is not located in the neutron beam.

Special reactor operation that is usually of very short duration.

 

Elements with atomic numbers greater than 92. These are called transuranic because they are man made and derived from uranium.

 

Waste containing alpha-emitting radio nuclides with an atomic number greater than 92 and half-lives greater than 20 years at concentrations greater than 100 nano curies per gram (nCi/g) without regard to source or form (e.g. plutonium, americium, curium, etc.)

 

An isotope of hydrogen containing two neutrons and one proton in its nucleus, therefore weighing three times as much as a hydrogen atom. Tritium is radioactive and can substitute water in the body, therefore posing a significant health risk.

 

A turbine is a large wheel that turns when a fluid (water, air, steam) moves over the blades. When a turbine moves, its energy can be used to turn a shaft that is connected to a generator, generating electricity. This is how nuclear energy is turned into electricity.

 

 

U

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U-235

Uranium 235; a rare, fissile isotope of uranium. U-235 is the only naturally occurring isotope that can be used to sustain a chain reaction. Only 0.7% of naturally occurring uranium is fissile U-235.

 

An atom that is in an excited energy state and therefore gives off energy in order to return to its ground, stable state. Radioactive isotopes are unstable and release energy in the form of radioactivity until they reach a stable state.

 

A naturally occurring heavy metal with atomic number 92. The two principal isotopes of natural uranium are fissile U-235, which is commonly used as nuclear fuel and fissionable U-238. U-235 is the only fissile isotope occurring in appreciable quantities in nature. Only 0.7% of naturally occurring uranium is U-235, the remaining 99.3% being U-238. Natural uranium is often enriched in order to increase the percentage of U-235 for use as nuclear fuel.

V

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W

The SI unit of power. Standard light bulbs use between 60 and 100 W. Power is often expressed in kilowatts (1kW = 1x103 W) or megawatts (1MW = 1x106 W).

 

X

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Highly penetrating radiation similar to gamma rays. Unlike gamma rays, X-rays do not come from the nucleus of the atom, but from the surrounding electrons. They are produced by electron bombardment. When these rays pass through an object they give a shadow picture of the denser portions.

Y

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Z

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A reactor that produces negligible power. These reactors are used for testing core configurations.