Nuclear Fission Glossary
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| A | B | C | D | E | F | G | H-K | O | R | S | T | U-Z |
A
absorbed dose
Symbol D, unit gray. The amount of energy absorbed per unit mass in a irradiated medium
actinide
Elements with atomic numbers between 89 and 103 including Uranium, Thorium and Plutonium
activation analysis
Analysis method used to measure the concentration of elements in samples by bombarding the sample with neutrons and measuring the energy and intensity of resulting gamma rays.
activity
Rate at which a radioactive material decays (in numbers of atoms per second) measured in curies.
advanced gas reactor (AGR)
Nuclear fission reactor which uses gas for cooling purposes.
alpha decay
A nuclear disintegration process where atoms of one element emit alpha particles.
alpha particle
(symbol α) A helium nucleus consisting of 2 protons and 2 neutrons and having a charge of +2.
alpha rays.
Alpha particles.
amu
Abbreviation for ‘atomic mass unit’
anomaly
A difference between a predicted and measured phenomena.
artificial radioisotopes
Radioactive materials which do not occur commonly in nature and must be manufactured by nuclear reactions.
atom
The smallest particle of an element that can combine with other atoms in a chemical reaction
atom bomb
General name for nuclear weapons
atomic clocks
Highly accurate and precise clocks which utilize the natural vibrations found within some atoms.
atomic mass unit
(Abbrev amu symbol u) A mass equivalent to one twelfth of the mass of on atom of carbon-12 or approximately 1.66 x 10-27 kg
atomic number
(Symbol Z) The number of protons in an atom.
atomic pile
Nuclear fission reactor
atomic weight
Also atomic mass, relative atomic mass (Symbol A). The average weight of a sample of an element expressed in atomic weight units.
B
background radiation
Radiation produced by the presence of local but unwanted sources of radiation such as cosmic rays and naturally occurring radioisotopes.
beam current
The charged particle current used in an electro or ion optical device such as a mass spectrometer, TV tube or electron microscope.
becquerel
(Symbol Bq) Unit of activity equal to one disintegration per second.
beta decay
(Symbol β) Radioactive decay where an atom decays into an isobar and emits either an electron or an antielectron (positron).
beta particle
A high speed electron or an antielectron (positron) emitted during beta decay.
billion
One thousand million.
Binding energy
The difference between the mass of an atomic nucleus and the mass of the constituent nuclei. A measure of nuclear stability.
boiling water reactor (BWR)
Nuclear reactor where water is used as the moderator and the coolant.
boron counter
A form of neutron detector.
breeder reactor
A nuclear reactor which generates nuclear fuel (sometimes as a by product) during its normal operation.
bremsstrahlung
Radiation emitted by electrons undergoing rapid deceleration (usually as they go through matter).
bubble chamber
Device used to detect ionized particles emitted by radioactive sources
burial
Deposition method for radioactive material.
burn-up
The transmutation or loss of a nuclide upon exposure to neutrons in a nuclear fission reactor. The nuclide adsorbs neutrons changing its mass number and may also beta decay to form a completely new element.
C
Cherenkov detector
A type of radiation detector used to detect Cherenkov radiation incorporating many photomultiplier tubes in an array to enable the path of the radiation to be determined.
Cherenkov radiation
A type of radiation which includes a bluish visible component in its spectrum. The radiation is analogous to the sonic boom phenomenon in sound and is caused by particles moving through a medium with a velocity greater than the velocity of light in that medium.
CERN
Centre d’Etudes Recherche Nucléaires. A Centre for research and nuclear studies based in Geneva, Switzerland.
chain reaction
A type of nuclear fission reaction in which the products (neutrons) act as important feed reactants for the next series of fission reactions. If the reaction is not controlled the reaction may multiply rapidly and cause a massive release of energy.
characteristic radiation
Radiation with a wavelength or frequency which is typical or expected for a a physical phenomenon. e.g., characteristic X-rays reflect the production mechanism and structure and number of electrons in the atoms of the X-ray generator being used.
cladding
The coating of one material with another. In nuclear reactors may be used to reduce corrosion. In optic fibres the fibres are coated to reduce signal loss and noise.
cold fusion
The unsubstantiated claim that nuclear fusion can be produced at room temperatures by using deuterium oxide and palladium electrodes.
control rod
Part of a control system used to control the rate of neutron reproduction (or the reaction of the reaction) in a nuclear reactor. The rods are usually made of cadmium metal or boron which have a very high neutron capture cross-section.
convection
Heat transfer from one place to another by movement of heated matter (usually fluid) brought about primarily because of the differences in buoyancy of warm and cool matter. The atmosphere and oceans are examples where this takes place on an everyday basis reflecting in the changes we observe in the weather.
convection current
A steady flow or stream within a fluid resulting from a difference in density between warm and cool sections of fluids.
convertor reactor
A type of nuclear reactor which produces new nuclear fuel during its operation. Typically the reactor contains another heavy nuclear material which when exposed to neutrons produces a more readily fissioned fuel.
coolant
Any material (usually fluid) used to reduce the temperature of a system by passing it over or around the system enabling it to absorb the heat by conduction and remove the heat by convection.
core
The main part of a nuclear reactor containing the nuclear fuel, moderator, monitoring system and the control rods.
counter
In radiation physics, a device used to monitor the number of particles emitted by a radioactive material. Some counters include sophisticated detectors and electronic amplification.
critical
The condition applied to a nuclear fission reaction which has reached a point where the number of neutrons being produced is matched by the number needed to sustain the reaction.
curie
(Symbol Ci) A unit of rate of radioactive disintegration equal to 3.7 x 1010 disintegrations per second now replaced by the becquerel (Bq) where 1 Ci equals 3.7 x 1010 Bq.
D
decay constant
(Symbol λ; unit ‘per second’) The probability or fraction of nuclei (of original number N) that will radioactively decay during a unit time (t), given by λ= -ΔN/Δt 1/N. Where the -ΔN/Δt is the actual number of disintegrations per unit time or the activity (A).
delayed neutrons
The neutrons produced by the beta decay of fission products.
detector
Any device or instrument used to sense the presence of a signal, detect the presence of radiation or particles, or convert a signal from one form to another.
deuteron
The nucleus of deuterium consisting of one proton and one neutron.
deuterium
The stable isotope of hydrogen with a nucleus which consists of one proton and one neutron. Chemically this atom behaves like hydrogen and is sometimes referred to as heavy hydrogen
E
enrich
To increase the abundance of an isotope of an element above that of the natural abundance.
enrichment
The percentage or fractional increase the abundance of an isotope of an element above that of the natural abundance.
epithermal neutron
An above room temperature neutron. A neutron with an energy in the range 0.01 to 100 eV which covers the range of energies of chemical bonds.
even-even nucleus
A nucleus having an even number of neutrons and an even number of protons. These nuclei are the most stable and represent over half of all nuclei.
even-odd nuclei
A nucleus having an even number of protons and an odd number of protons. These nuclei are less stable than even-even but more stable than even-odd nuclei.
exponential decay
The natural decrease in time of a quantity, such as the amount of a radioactive substance (N), which can be defined by the equation N(x) = Ae(bt ) where e is exponential function = 2.718 281 ..., t is time and A and b are constants. In the case of a radioactive material, A is the starting amount of that material and b is related to the inverse of the half life of that material.
F
fallout
Any of the range of possible radioactive materials that return to the ground following a surface or atmospheric nuclear explosion.
fast breeder reactor
A type of nuclear fission reactor which produces more nuclear fuel during its operating cycle than it consumes. A typical cycle is one which fissions 235U containing at ~95% 238U which is effectively non-fissionable. The 238U is converted by neutron capture into 239Pu which is extracted and reprocesses into new fuel.
fast fission
Nuclear fission induced by fast (MeV) neutrons.
fast neutrons
Neutrons with energies greater than about 0.1 MeV. Those with energies greater than 1.5 MeV can induce fission in 238U
fast reactor
A type of nuclear reactor which primarily uses the fast fission process for energy generation or nuclear research.
fissile
Any nucleus capable of being fissioned by slow neutrons.
fission
The splitting of high mass number nuclei by a variety of processes (usually involving neutrons) into two nuclei of smaller mass (usually radioactive) and releasing energy and more neutrons.
fissionable
Any nucleus capable of being fissioned by any nuclear interaction.
fuel element
The fundamental building block of nuclear fuel (uranium or plutonium) used to form fuel assemblies in a nuclear reactor. The fuel elements may be cylindrical or disc shaped and stacked to form rods or longer cylinders.
fusion
The combination of nuclei of light elements (hydrogen, deuterium and tritium) to produce a heavier nucleus, plus a significant amount of energy. This type of reaction requires a very large amount of energy (temperature) to initiate and a maintain a continuous reaction.
fusion reactor
A device designed to produced controlled nuclear fusion with the intention of extracting commercial quantities of energy from the process. Practical problems have included; the need to confine the very high (10 million degrees C) temperature of the plasma to a sufficient density and contamination of the plasma by external materials.
G
gamma rays
Electromagnetic radiation produced by atomic nuclei with wavelengths in the range of 10-10 to 10-14 m.
gamma ray spectra
The range of electromagnetic radiation produced by a gamma ray source including the scattered radiation from that source.
gamma ray transformation
A nuclear reaction accompanied by gamma ray emission.
gas cooled reactor
A type of nuclear reactor which uses an inert gas with a high thermal capacity and good thermal conduction as the coolant.
Geiger counter
A device used to count high energy radiation and particles, such as radioactivity. The counter consists of a Geiger tube or ionization chamber (which converts the incoming radiation into electronic pulses) and associated circuitry which amplifies and counts the pulses.
glove box
An apparatus consisting of a enclosure where one of the walls contains openings sealed by gloves used by human operators to safely manipulate beta and alpha radiation sources. The pressure in the box can usually be adjusted to reduce contamination from without or to prevent escape of radioactive material from the box.
H-K
half-life
(Symbol T1/2) The time takem for half of an amount of radioactive material to decay. T1/2 = 0.693/λ , where λ is the decay constant.
heavy water
Deuterium oxide. Water containing a higher than normal abundance of deuterium as the hydrogen component.
heavy water reactor
A type of nuclear reactor which uses heavy water as the moderator (and sometimes as the coolant) because of its significantly lower neutron capture cross section than normal hydrogen.
heterogeneous reactor
A nuclear reactor which uses a fuel which is physically separated from the moderator.
high temperature gas cooled reactor (HTR)
A type of nuclear reactor in which the core (fuel assembly) is incorporated in a ceramic type material and the coolant is a gas such as helium. This arrangement enables the reactor to operate with a much greater thermal efficiency by operating at a much higher temperature than usual.
homogeneous reactor
A nuclear reactor which uses a fuel and moderator are mixed together such as a solution (containing water as the moderator) of uranium (fuel).
JET
Joint European Torus experimental fusion reactor.
K-capture
Capture of electrons from the innermost layers (K shell) of the atom by atomic nuclei usually resulting in the production of highly energetic radiation.
K-shell electrons
Electrons existing in the most stable energy levels (with principle quantum number 1) within atoms. Usually electrons physically closest to the nucleus of atoms
kerma
(symbol: K, SI unit: gray) A measure of the total initial kinetic energy of ions formed by nuclear radiation in a small volume of a given material per unit mass of the material.
O
odd-even nucleus
Any one of the fifty or more nuclei with an odd number of protons and an even number of neutrons.
odd-odd nucleus
Any nucleus with both an odd number of protons and neutrons. Most are unstable but deuterium, Lithium-6, Boron-10 and Nitrogen-14 are stable.
R
rad
Old unit of absorbed dose of radiation equivalent to 10 mJ per kg of material (now replaced by the unit known as the gray=100 rad).
radiation
Any matter or energy which propagates as waves or particles or with ray like properties . Usually refers to all forms of electromagnetic radiation but often includes particles emitted from radiative materials.
radioactive
Any nucleus which spontaneously emits ionising radiation (alpha, beta or gamma radiation). Common abbreviation – RA.
radioactive series
Three groups of natural radioactive elements between mass numbers 92 (uranium) and 81 (bismuth) which form 3 sequences or series of radioactive parents and daughters. The series are named after the principal parent isotope, Uranium (Uranium 238), Thorium and Actinium (Uranium 235) and decay to the same element (but different isotope) of Lead.
radioactive tracer
A known amount of a radioactive substance added to an experiment usually to trace (with a geiger counter or similar equipment) the movement of the non-radioactive component of that element through the experiment. Such tracers have important uses in biology and chemistry.
radioactive waste
Any unwanted or unrecyclable material which is radioactive. Common sources are the nuclear energy and weapons industry and nuclear medicine facilities. Waste is usually grouped into high, intermediate and low levels depending on the danger to living organisims
radioactivity
The spontaneous change in the nuclear structure of an atomic nucleus usually accompanied by emission of subatomic particles and/or ionising radiation. The radiation can be alpha particles (helium nuclei), beta (positive or negative) particles (high speed positrons or electrons) and gamma (electromagnetic) radiation or a combination or any two or all three. Emission of beta and alpha particles changes the chemical nature of the atom concerned. Radioactivity can be entirely natural or produced artifically such as in a nuclear reactor or nuclear accelerator.
radioactive dating
The use of the natural change that occurs in the abundances of radioactive or ‘parent’ nuclei as they decay to a stable or ‘daughter’ nuclei in a material to measure the age of formation of that material. A large number of parent-daughter systems are available which covers a wide range of materials and age groups.
radiocarbon dating
Measurement of the age of formation of materials that contain carbon (such as bone, charcoal and plants) through the use of a natural change that occurs in the abundances of radioactive Carbon-14 (Halflife ~5000yrs) as it decays to Nitrogen-14. Carbon-14 is manufactured in the upper atmosphere by the solar wind. Some of this Carbon-14 is ingested through food by all living tissue during its lifetime until that organism dies whereby food uptake ceases and the ingested Carbon-14 continues to decay. This form of dating is usually restricted to ages less than 100,000 years. For ages greater than this other radioactive dating systems must be used.
radiogenic
Any effect, process or nuclei originating from radioactive decay (e.g., radiogenic isotopes are isotopes produced by radioactive decay).
radioisotope
A radioactive isotope or nucleus of an element
radiolysis
The breakup of chemicals into smaller components (e.g., water, H and O) by ionizing radiation.
radiometric age
The age (usually of a geological or once living material) as measured by radioactive dating. Compared for example to ‘fossil age’ which use the age of known fossils embedded or associated with that material or ‘dendrochronological age’ for trees which use the sequence of tree rings.
radionuclide
A radioactive nucleus
radiopaque
Materials which are more opaque to (usually ionizing) radiation than adjacent or surrounding materials. Usually refer to bone inside soft tissue.
rubidium-strontium dating
Measurement of the age of formation and evolutionary history of materials that contain the elements rubidium and strontium (such as rocks, meteorites and seawater) through the use of the natural radioactive decay of 87Rb (Halflife ~4700, 000, 000 yrs) as it decays to 87Sr. 87Rb is present from the initial formation of the solar system. When rocks or meteorites are formed, over time the subsequent decay of 87Rb increases the abundance of 87Sr in those materials. This effect of this process can be detected by measuring the amount of 87Sr using a mass spectrometer. Because of the very long half life this form of dating is usually restricted to ages greater than 100,000,000 years. For ages less than this other radioactive dating systems must be used.
rutherford
A unit of nuclear activity equivalent to one million events or disintegrations per second.
S
samarium-neodymium dating
Measurement of the age of formation and evolutionary history of materials that contain the rare earth elements samarium and neodymium (such as rocks, meteorites and seawater) through the use of the natural alpha decay of 143Sm (Halflife ~11 000, 000, 000 yrs) as it decays to 143Nd. The radioactive samarium 147 isotope is present at the initial formation of the solar system. When rocks or meteorites are formed, over time the subsequent decay of Sm increases the abundance of 143Nd in those materials. This effect of this process can be detected by measuring the amount of 143Nd and 147Sm using a mass spectrometer. Because of the very long half lives this form of dating is usually restricted to ages greater than 100,000,000 years. For ages less than this other radioactive dating systems must be used.
scintillation
Small pulses of visible radiation within a material produced by the interaction of inherent radioactivity within the material.
scintillation counter
A radiation detector based on the principle of scintillation whereby radiation produces small pulses of visible radiation within a material (such as as sodium iodide) as the radiation passes through that material. Associated photon amplification (photomultipliers) and counting circuitry convert the light into a train of voltage pulses with amplitudes proportional to the wavelength or energy of the individual radiation photons. The number of pulses are equivalent to the number of radiation counts per unit time.
shell model
A model often used to obtain mathematically and describe the energy levels possible for sub-atomic particles such as electrons around atomic nuclei and nucleons within a nucleus.
sievert
Symbol Sv. The SI unit of dose of radioactivity equal to 1J/kg.
Spontaneous fission (SF)
A form of nuclear radiation in which a nucleus (usually of a heavy nucleus) fissions without absorption of a neutron or other particle. All elements above mass 228 exhibit this property to some degree mostly with very long halflives. SF can initiate chain fission in a large enough assemblage of fissile material such as the first man made nuclear reactor which used natural U and graphite as the moderator.
stripping
A type of nuclear reaction where a nucleon in an incident nucleus is pulled out of its that nucleus without forming an intermediate compound nucleus with any target nucleus.
T
thermalize
The process of reducing the kinetic energy of a beam of particles (usually neutrons) to bring them into thermal equilibrium with their surroundings. This is usually done by utilizing energy loss through inelastic scattering such as passing the beam through matter with a low neutron capture cross section and containing particles of approximately the same mass. In the case of neutrons, water or solid blocks of paraffin wax are is used because of their high proton content.
thermal neutrons
Free neutrons which are in thermal equilibrium with their surroundings. In the case of neutrons this is usually considered to be a kinetic energy of 0.025 eV or a velocity of 2200 m/s.
thermal power station
An electrical power station which utilizes thermal energy (from oil, coal or nuclear) as a part of its electrical production system.
thorium-lead dating
Measurement of the age of formation and evolutionary history of materials that contain thorium and lead (such as rocks, meteorites and seawater) through the use of the natural radioactive decay of 232Th (Halflife ~4700, 000, 000 yrs) as it decays to 208Pb. The thorium is present at the initial formation of the solar system. When rocks or meteorites are formed, over time the subsequent decay of Th increases the abundance of 208Pb in those materials. This effect of this process can be detected by measuring the amount of 208Pb and 232Th using a mass spectrometer. Because of the very long half lives this form of dating is usually restricted to ages greater than 10,000,000 years. For ages less than this other radioactive dating systems must be used.
tokamak
A type of experimental fusion reactor in which a spiral magnetic field inside doughnut shaped tube is used to confine the high temperature plasma produced during fusion.
tracer
1. A known amount of a radioactive substance added to an experiment usually to trace (with a geiger counter or similar equipment) the movement of the non-radioactive component of that element through the experiment.
2. A known amount of an enriched stable isotope added to an experiment usually to determine the amount of the non-tracer component of that element using a mass spectrometer.
Such tracers have important uses in medicine, geology, biology and chemistry.
transuranic elements
The elements with atomic numbers between 90 and 103.
trition
A nucleus with two neutrons and one proton (tritium nucleus)
U-W
uranium – lead dating
A method of age determination of materials (esp minerals such as zircons) containing uranium which radioactively decays to lead over long periods of time. The measurements are performed using a mass spectrometer which measures the relative abundance of the uranium and lead isotopes.
uranium series
The radioactive isotopes produced during the decay of uranium to the stable isotopes of lead.
virgin neutrons
neutrons that have not yet been involved in any collisions.
Wigner nuclides
Two mirror nuclides A and B where A has the same number of protons (p) as B has numbers of neutrons (n) with the added condition of both having mass numbers of (2p + 1)
Wilson cloud chamber
A device which exposes the tracks left by radiation or ionizing particle by providing a set of pressure and humidity conditions in a chamber such that the particles provide nucleation sites to form a trail of moisture droplets.
window
A thin sheet of material covering the end of a radiation detector through which radiation can enter with minimal absorption.
References:
1985 CRC Handbook of Chemistry and Physics, Weast, R.C Ed, CRC Press Inc. Boca Raton, Florida.
1991 Penguin Dictionary of Physics
