Glossary of Nuclear Science Terms

A B C D E F G H I J K L M N O P R S T U V W Y Z

- A -

Any material that stops ionizing radiation. Lead, concrete, and steel attenuate gamma rays. A thin sheet of paper or metal will stop or absorb alpha particles and most beta particles.
Accelerator: A machine, in which charged particles (electrons, protons, their anti-particles, heavy ions etc.) may be accelerated in suitably shaped electric and magnetic fields. Depending on the accelerated particle paths, two classes may be distinguished: ring and linear accelerators.
Particles accelerated to very high energies (billions of electronvolts, GeV) or extremely high energies (millions of millions of electronvolts, TeV) are used in basic research on structure of the matter. In a few places around the globe large research ring accelerators with diameters on the order of kilometers have been built. European scientists mainly use the facilities available in the CERN research center (Geneva, Switzerland).

Particles accelerated to MeV energies find important applications in industry and medicine. Number of such accelerators (mainly linear electron accelerators applied in oncology radiotherapy) is estimated to a few thousand in the world (around 30 such machines works in Poland).
Alpha particle (alpha radiation, alpha ray): A positively charged particle made up of two neutrons and two protons (a Helium-4 nucleus). It is the least penetrating of the three common forms of radiation, being stopped by a sheet of paper. It is not dangerous to living things unless the alpha-emitting substance is inhaled or ingested or comes into contact with the lens of the eye.
Anti-particles: Corresponding partners of particles with equal mass but otherwise opposite properties, e.g. opposite electric charge, baryon number, strangeness). If a particle collides with its anti-particle, both annihilate to form photons or other particles.
Antimatter: Matter composed of antiparticles
Atom: A particle of matter indivisible by chemical means. It is the fundamental building block of elements.
Atomic number: The number assigned to each element on the basis of the number of protons found in the element's nucleus.
Atomic weight (atomic mass): Approximately the sum of the number of protons and neutrons found in the nucleus of an atom.

- B -

Background radiation: The radiation of man's natural environment originating primarily from the naturally radioactive elements of the earth and from the cosmic rays. The term may also mean radiation extraneous to an experiment.
Becquerel (Bq): Unit of radioactive substance activity: 1 Bq = 1 disintegration per second.
Beam: Collimated flux of particles (from a radioactive source, accelerator, nuclear reactor etc.) or photons (X or g). Beams of charged particles -- especially those produced in accelerators -- are formed by combination of suitably shaped electric and magnetic fields. Beams of neutrons, other electrically neutral particles and photons are formed by collimators i.e. suitably chosen absorbers with openings.
Beta particle (beta radiation, beta ray): An electron of either positive charge (ß+) or negative charge (ß-), which has been emitted by an atomic nucleus or neutron in the process of a transformation. Beta particles are more penetrating than alpha particles but less than gamma rays or x-rays.
Big Bang: Origin of the Universe. State of extremely high energy density from which the Universe evolved by expansion and simultaneous cooling.

- C -

Contamination: Radioactive material deposited or dispersed in materials or places where it is not wanted.
Curie (Ci): The basic unit used to describe the intensity of radioactivity in a sample of material. One curie equals thirty-seven billion disintegrations per second, or approximately the radioactivity of one gram of radium.

- D -

Dark matter: These parts of the Universe, which do not radiate energy and therefore can not be directly observed. Dark matter presence is concluded from observations of various gravitation effects. Recently the belief that the dark matter constitutes majority of all the matter of the Universe has been grounded.
Daughter: A nucleus formed by the radioactive decay of a different (parent) nuclide.
Decay (radioactive): The change of one radioactive nuclide into a different nuclide by the spontaneous emission of alpha, beta, or gamma rays, or by electron capture. The end product is a less energetic, more stable nucleus. Each decay process has a definite half-life.
Decontamination: The removal of radioactive contaminants by cleaning and washing with chemicals.
Dose: A general term denoting the quantity of radiation or energy absorbed in a specific mass.

- E -

Electromagnetic radiation: Radiation consisting of electric and magnetic waves that travel at the speed of light. Examples: light, radio waves, gamma rays, x-rays.
Electron: An elementary particle with a unit electrical charge and a mass 1/1837 that of the proton. Electrons surround the atom's positively charged nucleus and determine the atom's chemical properties.
eV (electron-volt): Unit of energy used by nuclear and atomic physicists. 1 eV = 1.6·10^-19 J is an energy acquired by a particle carrying 1 elementary electric charge 1 e = 1,6·10^-19 C (eg. electron or proton) accelerated by 1 V potential difference.
Electron capture: A radioactive decay process in which an orbital electron is captured by and merges with the nucleus. The mass number is unchanged, but the atomic number is decreased by one.
Eluant: Washing solution (The solution that is introduced into radioisotope generator system).
Eluate: The washings obtained by elution (the solution that comes out of the radioisotope generator system).
Elute: To separate by washing (to milk a radioisotope generator system).
Excited state: The state of an atom or nucleus when it possesses more than its normal energy. The excess energy is usually released eventually as a gamma ray.

- F -

Fission: The splitting of a heavy nucleus into two roughly equal parts (which are nuclei of lighter elements), accompanied by the release of a relatively large amount of energy in the form of kinetic energy of the two parts and in the form of emission of neutrons and gamma rays.
Fission products: Nuclei formed by the fission of heavy elements. They are of medium atomic weight and almost all are radioactive. Examples: strontium-90, cesium-137.
Fusion: The combining of two light nuclei into a single heavier one. Energy released in such reaction is several times larger than that released in the fission reaction since light nuclei have several times lower binding energies than the heaviest ones. Fusion happens naturally inside stars that shine until there is an ample supply of the lightest nuclei (hydrogen, deuterium, tritium). The star with "burned fuel" collapses and - depending on its mass - quietly goes out or else explodes as novae or supernovae. The latter may happen if the dying star mass is sufficiently large to generate (during the process of gravitational collapse) an energy sufficient to ignite fusion of the remaining heavier nuclei. The remnant of a super/novae explosion is a cold neutron star.

- G -

Gamma ray: A highly penetrating type of nuclear radiation, similar to X-radiation, except that it comes from within the nucleus of an atom, and, in general, has a shorter wavelength.
Geiger counter: A Geiger-Müller detector and measuring instrument. It contains a gas-filled tube which discharges electrically when ionizing radiation passes through it and a device that records the events.
Gray (Gy): Unit of absorbed dose. 1 Gy = 1 J of radiative energy absorbed within 1 kg of an absorber.

- H -

Hadrons: Particles composed of quarks, bound by strong interactions. Two basic kinds of hadrons are: baryons composed of 3 quarks, and mesons composed of 2 quarks.
Half-life: The time in which half the atoms of a particular radioactive nuclide disintegrate. The half-life is a characteristic property of each radioactive isotope.
Health physics: That science devoted to recognition, evaluation, and control of all health hazards from ionizing radiation.

- I -

Induced radioactivity: Radioactivity that is created by bombarding a substance with neutrons in a reactor or with charged particles produced by particle accelerators.
Ion: An atomic particle that is electrically charged, either negative or positive.
Ionizing radiation: Radiation that is capable of producing ions either directly or indirectly (e.g. cosmic showers).
Irradiate: To expose to some form of radiation.
Isobars: Nuclides with the same mass number (sum of neutrons and protons) but different atomic numbers (number of protons).
Isomers: Nuclides with the same mass and atomic numbers capable of existing for a measurable time in different energy states. Most isotopes do not have any isomers, but some may have several. Isomers are designated with "m" placed after the mass number eg. ^99mTc (technetium-99m).
Isomeric transition: A mode of radioactive decay where a nucleus goes from a higher to a lower energy state. The mass and atomic numbers are unchanged.
Isotones: Nuclides with the same number of neutrons. Example: ³⁷Cl, ³⁸Ar, ³⁹K and ⁴⁰Ca have 20 neutrons each.
Isotopes: Nuclides with the same atomic number (the same number of protons i.e. the same element) but different mass numbers (i.e. different number of neutrons), eg. uranium-238 and uranium-235. Only some isotopes of a given element are usually stable while other are radiactive. Many radiactive isotopes do not exist naturally, but they may be produced in a nuclear lab if a need for them arises.

- K -

K-capture: The capture by an atom's nucleus of an orbital electron from the first K-shell surrounding the nucleus.
keV: One thousand electron volts.

- L -

- M -

Mass number: Mass given in u units, defined as 1 u = 1/12 mass of an atom of carbon isotope ¹²C = 1,66·10^-27 kg (by definition mass of ¹²C amounts to exactly 12.0000 u). Since mass of a neutron and mass of a proton is nearly equal to 1 u, mass number of a given nucleus is (to the first approximation) the sum of number of protons and number of neutrons in that nucleus.
MeV: One million electron volts.
Microcurie (µCi): One millionth of a curie (3.7·10⁴ disintegrations per second).

- N -

Neutrino: An electrically neutral particle with negligible mass. It is produced in many nuclear reactions such as in beta decay.
Neutron: One of the basic particles which make up an atom. A neutron and a proton have about the same weight, but the neutron has no electrical charge.
Neutron star: Small (diameter around 10 km) remnant of a super/novae explosion. Density of the neutron star is extremely high since its matter is composed practically solely of neutrons.
Nuclear medicine: Part of medicine dealing with nuclear techniques (mainly radioactive isotopes and particle accelerators) in diagnostics and treatment of patients.
Nuclear reactor: A device in which a fission chain reaction can be initiated, maintained, and controlled. Its essential components are fissionable fuel, moderator, shielding, control rods, and coolant.
Nucleon: A constituent of the nucleus; that is, a proton or a neutron.
Nucleonics: The science, technology, and application of nuclear energy.
Nucleus: The core of the atom, where most of its mass and all of its positive charge is concentrated. Except for hydrogen, it consists of protons and neutrons.
Nuclide: Any species of atom that exists for a measurable length of time. A nuclide can be distinguished by its atomic weight, atomic number, and energy state.

- O -

- P -

Parent: A radionuclide that decays to another nuclide which may be either radioactive or stable.
Photon: A quantity of electromagnetic energy. Photons have momentum but no mass or electrical charge.
Plasma: Very hot matter (when atoms are ionized). Due to specific properties of mixtures of free electrons and ions plasma is often called "the fourth state of the matter".
Proton: One of the basic particles which makes up an atom. The proton is found in the nucleus and has a positive electrical charge equivalent to the negative charge of an electron and a mass similar to that of a neutron: a hydrogen nucleus.

- Q -

- R -

Rad: Radiation Absorbed Dose. The basic unit of an absorbed dose of ionizing radiation. One rad is equal to the absorption of 100 ergs of radiation energy per gram of matter.
Radioactive dating: A technique for estimating the age of an object by measuring the amounts of various radioisotopes in it.
Radioactive waste: Materials which are radioactive and for which there is no further use
Radioactivity: The spontaneous decay or disintegration of an unstable atomic nucleus accompanied by the emission of radiation.
Radioisotope: A radioactive isotope. A common term for a radionuclide.
Radioisotope generator: (cow) A system containing a parent-daughter set of radioisotopes, in which the parent decays through a daughter to a stable isotope. The daughter is a different element from that of the parent, and hence can be separated from the parent by elution (milking).

Radionuclide: A radioactive nuclide. An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation.
Radiotherapy: One of three principal methods of combating cancer tissue involves irradiating it with ionizing radiation. Modern radiotherapy methods are based on linear accelerators of electrons and other charged particles.
Rate meter: An electronic instrument that indicates, on a meter, the number of radiation induced pulses per minute from radiation detectors such as a Geiger-Muller tube.

- S -

Scaler: An electronic instrument for counting radiation induced pulses from radiation detectors such as a Geiger-Muller tube
Scintillation counter: An instrument that detects and measures gamma radiation by counting the light flashes (scintillations) induced by the radiation.
Secular equilibrium: A state of parent-daughter equilibrium which is achieved when the half-life of the parent is much longer than the half-life of the daughter. In this case, if the two are not separated, the daughter will eventually be decaying at the same rate at which it is being produced. At this point, both parent and daughter will decay at the same rate until the parent is essentially exhausted.
Shielding: A protective barrier, usually a dense material, which reduces the passage of radiation from radioactive materials to the surroundings
Sievert (Sv): Unit of equivalent dose. The concept of equivalent dose takes into account radiation quality, ie. different reaction of biogical tissue on different kinds of radiation. For X and gamma rays 1 Sv = 1 Gy.
Source: A suitably packed radioactive material that produces radiation for experimental or industrial use
Spill: The accidental release of radioactive materials.
Stable: Non-radioactive.
Strong interaction: One of four principal kinds of physical interactions (gravitational, electromagnetic, weak, strong). It binds together quarks within elementary particles via constantly exchanged gluons. It is a very short-range interaction.

- T -

Tracer: A small amount of radioactive isotope introduced into a system in order to follow the behavior of some component of that system.
Transmutation: The transformation of one element into another by a nuclear reaction

- U -

- V -

- W -

- X -

- Y -

- Z -