Atom: A particle of matter which cannot be broken up 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 a number of negatively-charged electrons in motion around the nucleus.
Absorbed dose: Absorbed dose is the amount of radiation absorbed in an organ or tissue (i.e., the amount of radiation energy that has been deposited in cells, tissues, or organs). Absorbed dose is usually defined as energy deposited (joule) per unit of mass (kilogram). Absorbed dose is used for purposes of radiation protection and assessing dose or risk to humans in general terms. See gray and rad.
Alpha particle: An alpha particle is a particle with weight and charge. It is made up of two protons – positively charged – and two neutrons. . Alpha particles do not travel very far and are not considered an exposure hazard unless the radioactive material that emits them gets inside the body.
ALARA (As low as reasonably achievable): ALARA is a principle of radiation protection that calls for practical efforts to be taken to keep exposures to ionizing radiation as low as reasonably achievable, economic and social factors being taken into account.
Background radiation: Background radiation – also known as natural background radiation- includes radiation from cosmic sources, naturally occurring radioactive materials (including radon), and global fallout (from the testing of nuclear explosive devices). The typically quoted world average individual exposure from background radiation is 2.4 mSv per year. But the dose varies greatly depending on location, and can be as 30 times the average, for example in areas of Kerala state in India.
Becquerel: A Becquerel (Bq) measures the activity of a quantity of radioactive material in which one nucleus decays per second. The becquerel, part of the International System of Units (SI), succeeded the curie (Ci), an older, non-SI based on the activity of 1 gram of radium-226. One curie is equal to 3.7 x 1010 Bq, or 37 gigabecquerels (GBq). See curie.
Beta particle: A beta particle is a high-energy electron or positron emitted , during radioactive decay. Beta particles do not travel very far, but travel farther than alpha particles. Beta particles are typically stopped by about 30 millimeters or about an eighth (1/8) of an inch of fabric; higher-energy beta particles will be stopped by approximately a centimeter of fabric. Beta particles do have a charge—those that are negatively charged are electrons and those that are positively charged are called positrons.
Contamination: Contamination is the presence of radioactive material where it is not wanted—most commonly by depositing on surfaces or inside structures, objects, or people.
Coolant: In a nuclear power plant, the liquid or gas used to transfer heat from the reactor core to the steam generators or directly to the turbines.
Core: The central part of a nuclear reactor containing the fuel assemblies, neutron moderator if there is one, the means to control the nuclear reaction (control rods), and coolant.
Cosmic radiation: Cosmic radiation is penetrating ionizing radiation comprised of particles and electromagnetic energy that comes from outer space. Cosmic radiation accounts for about half of the annual worldwide natural background radiation exposure
Curie: The curie (Ci) is the original term used to describe the activity of a given quantity of radioactive material (such as the strength of a source). It is based upon the radioactive decay rate of 1 gram of radium-226 . This unit is still used in some contexts but was succeeded in the International System of Units by the becquerel, which is equal to one atomic disintegration per second. One curie is equal to 3.7 x 1010 Bq The most common activity levels used in laboratories are the millicurie (mCi) and microcurie (µCi). A millicurie (mCi) is 1/1,000 th of a curie and a microcurie (µCi) is 1/1,000,000 th of a curie
Decommissioning: Removal of a facility (e.g. reactor) from service, also the subsequent actions of safe storage, dismantling and making the site available for unrestricted use.
Decontamination: Decontamination is a process through which radioactive materials (or other hazardous materials) are removed from surfaces (e.g., laboratory working areas) through cleaning and washing, as well as from solutions.
Dose: Dose is a general term used to express (quantify) how much radiation exposure something (a person or other material) has received. The exposure can subsequently be expressed in terms of the absorbed, equivalent, committed, and/or effective dose, based on the amount of energy absorbed and in what tissues.
Effective dose: Radiation exposures to the human body, whether from external or internal sources, can involve all or a portion of the body. The health effects of one unit of dose to the entire body are more harmful than the same dose to only a portion of the body, for example the hand or the foot. To enable radiation protection specialists to express partial-body exposures (and the accompanying doses) to portions of the body in terms of an equal dose to the whole body, the concept of effective dose was developed. Effective dose, then, is the dose to the whole body that carries with it the same risk as a higher dose to a portion of the body. As an example, 8 rem (80 milliSievert) to the lungs is roughly the same potential detriment as 1 rem (10 mSv) to the whole body based on this idea.
Electromagnetic spectrum: The electromagnetic spectrum is the broad range of radiation that includes radio waves; microwaves; infrared, visible, and ultraviolet light; and x and gamma rays.
Element: A chemical substance that cannot be divided into simpler substances by chemical means; atomic species with same number of protons (being the atomic number of the element).
Equivalent dose: Equivalent dose is a dose quantity used for radiation protection purposes that takes into account the chance that a type of radiation will cause an effect. Different types of radiation (alpha, beta, gamma) interact with human tissues differently, with some leaving a lot of energy in the tissue and others leaving very little energy in the tissue, and the energy that is left is what partially determines whether an effect will occur or not. Because of this, different types of radiation are assigned numbers based on how effective that type of radiation is at leaving its energy in the tissue, thus having more potential to cause an effect. The use of equivalent dose provides an indication of the potential for biological effects. From this, risk comparisons can be made between the different types of radiation.
Exposure: Exposure is commonly used to refer to proximity to a radiation source, e.g., if you have a chest x ray, you are exposed to radiation. By definition, exposure is a measure of the quantity of ionisations produced in air by photon radiation (gamma radiation or x-rays). In the nuclear industry, the unit used is commonly the roentgen (R).
Exposure rate: Exposure rate is the amount of exposure per unit time (e.g., 1 mR/hour). Dose rate is the amount of dose per unit time (e.g., 1 mrem/hour).
Fertile (of an isotope): Capable of becoming fissile, by capturing neutrons, possibly followed by radioactive decay; e.g. U-238, Pu-240.
Fissile (of an isotope): Capable of capturing a slow (thermal) neutron and undergoing nuclear fission, e.g. U-235, U-233, Pu-239.
Fission: The splitting of a heavy nucleus into 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.
Gamma rays: Gamma rays are high-energy electromagnetic radiation (photons) emitted in an attempt by the radionuclide to become stable, i.e., radioactive decay. Gamma rays have moderate-to-high penetrating power, are often able to penetrate deep into the body, and generally require some form of shielding, such as lead or concrete. Visible light is also in the form of photons. Gamma photons behave similarly to light, but they are invisible.
Gray: Gray (Gy) is the unit in the International System of Units to replace the rad (see rad).
Half-life: Also called radiological or physical half-life, this is the amount of time it takes for half of the radioactivity in a material to disappear or to decay. The half-life of a radionuclide can be fractions of a second or up to millions of years. As an example, the half-life of iodine-131 is eight days. If we start with 10 radioactivity units of iodine-131, after eight days we have five radioactivity units, or half the amount we started with. After eight more days (16 total), we would have 2½ radioactivity units left, or a fourth of what we started with. Physical or radioactive half-life refers to reduction of radioactivity by radioactive decay; biological half-life refers to elimination of internal radioactivity – that is, radioactive material ingested into the body – by biological processes in a biological system, and effective half-life is a combination of radioactive decay and biological elimination.
High-level waste or wastes: Extremely radioactive fission products and transuranic elements (usually other than plutonium) in used nuclear fuel. They may be separated from used fuel through chemical processing, known as reprocessing ,. Unreprocessed used fuel may also be regarded as high-level waste.
Ionisation: Ionisation is the process by which a neutral atom (an atom with no charge) gains a positive or negative (electrical) charge.
Ionising radiation: Radiation that is capable of producing ions by passing through matter. See Radiation
Irradiate: To irradiate is the act of exposing someone or something to radiation. Irradiated food is food that has been exposed to radiation. For example, irradiation can be used to preserve the shelf life of foodstuffs by killing or decreasing the impact of harmful micro-organisms.
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 (qv) to form isotopes of other elements.
Low-level wastes: Mildly radioactive material, usually disposed of by incineration and burial.
Monitoring: Monitoring is the act of using instruments to look for radiation and is also the measurement of radiation exposure levels or radionuclide quantities.
Neutron: A neutron is an elementary particle that is electrically neutral and found in the nucleus of every atom except hydrogen. Neutrons have no electric charge and are usually highly penetrating.
Personal radiation dosimeter: More widely known as a radiation “badge,” a personal radiation dosimeter is a device worn by an individual to determine the radiation dose he or she has received.
Rad: Rad is the term used to describe absorbed radiation dose. It describes a specific amount of energy absorbed in a medium (human tissue, for example). In the International System of Units, the gray (Gy) describes absorbed radiation dose. One gray is equal to 100 rad.
Radiation: The emission and propagation of energy by means of electromagnetic waves or particles. Radiation is a term commonly used to describe ionizing radiation (i.e., x and gamma rays, alpha and beta particles, neutrons).
Radiation-measuring instrument: A radiation-measuring instrument is a device or system used to detect if radiation is present and/or how much and what type of radiation is present. Common instruments are Geiger-Mueller detectors (GM), scintillation detectors (such as sodium iodide detectors), and ion chambers.
Radioactive decay: Radioactive decay is the spontaneous transformation of one nuclide into another nuclide or different energy state, in an attempt to reach a stable state. In the transformation process, radiation is emitted (as particles or waves) and the nuclide loses both energy and mass
Radioactive material: Radioactive material is material that contains radioactivity and thus emits ionising radiation. It may be material that contains natural radioactivity from the environment or a material that may have been made radioactive (see radioactivity).
Radioactivity: Radioactivity is the property of a nucleus in unstable atoms that causes them to spontaneously release energy in the form of photons (e.g., gamma rays) or subatomic particles (e.g., alpha or beta particles).
Radiological: Radiological is an adjective pertaining to radiation and radioactive materials.
Radionuclide: A radionuclide is a radioactive element, man-made or from natural sources, with a specific atomic weight.
Rem: Rem is the term used to describe equivalent or effective radiation dose. In the International System of Units, the sievert (Sv) describes equivalent or effective radiation dose. One Sievert is equal to 100 rem. It is a unit that is the product of energy absorbed in human tissues and the quality of the radiation being absorbed (the ability of the radiation to cause damage).
Roentgen (R): The roentgen (R) is the term used to describe radiation exposure. This term for exposure only describes the amount of ionization in air. In the International System of Units, the coulomb/kilogram (c/kg) describes radiation exposure. One roentgen is equal to 2.58 x 10 -4 c/kg.
Sealed source: A sealed source is a radioactive source sealed in a container (e.g., a tightly welded metal capsule) that does not allow the radioactive substance (contamination) to escape.
Sievert: Sievert (Sv) is the unit in the International System of Units to replace the rem (see rem).
Threshold: Threshold is the point at which radiation first produces an observable effect (response) from exposure.
Used fuel: Also known as spent fuel. Fuel removed from a nuclear reactor after irradiation which can either be reprocessed – i.e., put through a chemical process to separate the streams of uranium and plutonium that can be further used from other products that have no further energy use and thus are classified as waste – or stored for later emplacement in a waste repository.
Waste: High-level waste (HLW) is highly radioactive material arising from nuclear fission. It can be what is left over from reprocessing used fuel, though some countries regard spent fuel itself as HLW. It requires very careful handling, storage and disposal, typically deep underground. Low-level waste (LLW) is mildly radioactive material usually disposed of by incineration and burial in surface or subsurface facilities. Intermediate-level waste (ILW) is the term used to designate either waste that is slightly more active than low-level waste, or waste that contains long-lived elements (such as americium or curium) that are not accepted for surface or shallow-land burial. Reprocessing creates significant amounts of separated long-lived ILW.
X-rays: X-rays are electromagnetic radiation (photons) that can be emitted from radionuclides or by certain types of devices. Generally, x-rays have lower energies than gamma rays, but like gamma rays, x-rays can penetrate into the body. Sometimes lead or concrete may be used as a shielding material to reduce the penetration of x-rays.