Radiation Definitions



Activity- the rate of disintigration (transfermation) or decay of radioactive material. the ubits of activity are the curie (Ci) and the becquerel (Bq).

Acute exposure- Exposure over a short amount of time.OR the absorption of a relatively large amount of radiation(or intake of radiation material) over a short period of time.

Agreement State- Any state with which the US NRC or the US AEC has entered into an effective agreement under subsection 274b of the Atomic Energy Act of 1954, as amended (73 Stat 689).

Alpha- A doubly positive charged particle ejected spontaneously from the nuclei of some radioactive elements. It has a mass of 4 AMU and has low penetrating power and a short range. The most energetic alpha particle will generally fail to penetrate the dead layers of cells covering the skin. Alphas are hazardous when an alpha-emitting isotope is inside the body.

Annual limit on Intake (ALI) - the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. ALI is the smaller value of intake of a given radionuclide in a year by reference man that would result in a CEDE of 5 rems (0.05 Sv) or a CDE of 50 rem (0.5 Sv) to any individual organ or tissue.

Atomic number - The number of positively charged protons in the nucleus of an atom and the number of electrons in an electronically neutral atom.

Becquerel - A unit, in the International System of Units (SI), of measurement of radioactivity equal to one transfermation per second.

Beta- A negatively charged particle emitted from a nucleus during radioactive decay, with a mass equal to 1/1837 that of a proton. A beta particle is identical to an electron. A positively charged beta particle is called a positron. Large amounts of beta radiation may cause skin burns, and beta emitters are harmful if they enter the body. Beta particles may be stopped by thin sheets of metal or plastic.

Bioassay - The determination of kinds, quantities or concentrations, and , in some cases, the locations of radioactive material in the human body, whether by direct measurement or by analysis and evaluation of materials excreted or removed from the human body.

Biological Half-life - The time required for a biological system, such as that of a human, to eliminate by natural processes half the amount of a sustance that has entered the body.

Brachytherapy - A method of radiation therapy in which sealed sources are utilized to deliver a radiation dose at a distance of up to a few cm, by surface, intracavitary, or interstitial.

Bremstrahlung - Secondary photon radiation produced by deceleration of charged particles through matter.

Cask - A heavily shielded container used to store and/or ship radioactive materials.

Chronic Exposure - The absorption of radiation (or intake of radioactive materials over a long period of time)

Committed Dose Equivalent (CDE) The dose equivalent to organs or tissues of reference that will be received from an intake of radioactive material by an individual during the 50-year period following the intake.

Committed Effective Dose Equivalent (CEDE) The sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the CDE to these organs or tissues.

Contamination The deposition of unwanted radioactive material on the surfaces of structures, areas, objects, or personnel.

Cosmic Radiation Penetrating ionizing radiation, both particulate and electromagnetic, originating in space.

Critical Mass The smallest mass of fissionable material that will support a self-sustaining chain reaction.

Curie (Ci) The basic unit used to describe the intensity of radioactivity in a sample of material. The curie is equal to 37 billion disintegrations per second, which is approximately the rate of decay of one gram of radium. Named for Marie and Pierre Curie, who discovered radium in 1898.

Decay, radioactive The decrease in the amount of any radioactive material with the passage of time, due to the spontaneous emission from the atomic nuclei of either alpha or beta particles, often accompanied by gamma radiation.

Derived Air Concentration (DAC) The concentration of a given radionuclide in air which, if breathed by the reference man for a working year of 2000 hours under conditions of light work (1.2 cubic meters per hour), results in an intake of one ALI.

Deuterium - An Isotope of Hydrogen with one proton and one neutron in the nucleus.

Dose Equivalent The product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest. Units are Rem and Sv

Dosimeter - A portable instrument for measuring and registering the total accumulated exsposure to ionizing radiation.

Effective Dose Equivalent (EDE) The sum of the products of the dose equivalent to the organ or tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated.

Electromagnetic radiation A traveling wave motion resulting from changing electric or magnetic fields. Examples of electromagnetic radiations are x-rays, ultraviolet, visible light, radar, and radio waves. All electromagnetic radiations travel in a vacuum with the velocity of light.

Electron- An elementary particle with a negative charge and a mass 1/1837 that of the proton. Electrons surround the positively charged nucleus and determine the chemical properties of the atom.

Element One of the 108+ known chemical substances that cannot be broken down further without its chemical properties.

Film badge A pack of photographic film used for approximate measurement of radiation exposure for personnel monitoring purposes.

Fission The splitting of nucleus into at least two other nuclei and the release of a relatively large amount of energy.

Fusion A nuclear reaction characterized by joining together of light nuclei to form heavier nuclei, the energy for the reactions being provided by the violent thermal agitation of particles are very high temperatures. The energy of the stars is derived from fusion reactions.

Gamma Ray- High-energy, short wavelength, electromagnetic radiation (a packet of energy) emitted from the nucleus. Gamma radiation frequently accompanies alpha and beta emissions and always accompanies fission. Gamma rays are very penetrating and are best stopped or shielded by dense materials, such as lead or uranium. Gamma rays are similar to X-rays.

Half-life- The time in which one half of the atoms of a particular radioactive substance disintegrates into another nuclear form. Measured half-lives vary from millionths of a second to billions of years.

Health Physics The science concerned with recognition, evaluation, and control of health hazards from ionizing and non-ionizing radiation.

Intake Quantity of material introduced into the body by inhalation, by ingestion, or through the skin.

Ionization chamber An instrument that detects and measures ionizing radiation by measuring the electrical current that flows when radiation ionizes gas in a chamber, making the gas a conductor of electricity.

Ionizing Radiation- Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions. Some examples are alpha, beta, gamma, X-rays, neutrons. High doses of ionizing radiation may produce severe skin or tissue damage.

Irradiation Exposure to radiation.- Isotope One of two or more atoms with the same number of protons, but different numbers of neutrons in their nuclei. Thus, carbon-12, carbon-13, and carbon-14 are isotopes of the element carbon, the number denoting the approximate atomic weights. Isotopes have very nearly the same chemical properties, but often different physical properties (for example, carbon-12 and -13 are stable, carbon-14 is radioactive).  Neutron An uncharged elementary particle with a mass slightly greater than that of the proton, and found in the nucleus of every atom heavier than hydrogen.

Isotope One of two or more atoms with the same number of protons, but different number of neutrons, in their nuclei. Carbon 12, Carbon-13, and Carbon-14 are examples of isotopes.

Linear energy transfer A measure of the ability of biological material to absorb ionizing radiation, specifically for charged particles traversing a medium the energy lost per unit length of path as a result of those collisions with electrons in which energy loss is less than that specified maximum value.

Mass number The number of nucleons (protons and neutrons) in the nucleus of an atom. Also known as the atomic weight.

Noble gas A gaseous chemical that does not readily enter into chemical combination with other element.

Nonstocastic effect Health effects the severity of which varies with the dose and for which a threshold is believed to exist. Radiation induced cataracts is an example.

Nucleus The small, central, positively charged region of the atom that carries essentially all the mass. All nuclei, except normal Hydrogen, have protons and neutrons in the nucleus.

Nuclide a general term referring to all known isotopes, both stable and unstable, of the chemical elements.

Periodic Table An arrangement of chemical elements in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding groups or families of elements.

Photon A quantum (or packet) of energy emitted in the form of electromagnetic radiation. Gamma rays and X-rays are examples.

Positron Particle equal in mass, but opposite in charge, to the electron.

Proton- An elementary nuclear particle with a positive electric charge located in the nucleus of an atom. The number of protons in a nucleus determines the element.

Quality Factor The modifying factor that is used to derive dose equivalent from absorbed dose.

RAD the special unit of absorbed dose. The rad is equal to an absorbed dose of 100 ergs/gram or 0.01 J/kg or 0.01 gray.

Radiation area An area, accessable to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 0.005 rem (0.05mSv) in one hour at 30 cm from the radiation source or from any surface that the radiation penetrates.

Radiation Sickness (syndromes) The complex of symptoms characterizing the disease known as radiation injury, resulting from excessive exposure of the whole body to ionizing radiation.  The earliest of these symptoms are nausea, fatigue, vomiting, and diarrhea, which may be followed by loss of hair, hemorrhage, inflammation of the mouth and throat, and general loss of energy. The syndromes progress from Prodromal to hematopietic, gastrointestinal, and finally to central nervous system.

Radioactivity- The spontaneous emission of radiation, generally alpha or beta particles, often accompanied by gamma rays, from the nucleus of an unstable isotope.

Radon- An invisible, radioactive gas that occurs naturally in soil. Radon is a daughter of radium and one of the heaviest gases known. Radon is responsible for about 50% of your total radiation dose in the U.S.

Reference man A hypothetical aggregation of human physical and physiological characteristics arrived at by international consensus and can be used to relate biological insult to a common base.

Rem The special unit of any of the quantities expressed as dose equivalent. (1 rem = 0.01 Sv).

Roentgen (R) A unit of exposure of ionizing radiation. Named after Wilhelm Roentgen, a German scientist who discovered X-rays in 1895.

Sievert The SI unit of any of the quantities expressed as dose equivalent. The dose equivalent in equal to the absorbed dose (gray) multiplied by the quality factor. (1 Sv = 100 rem)

Somatic Effect Effects of radiation limited to the exposed individual.

Stochastic Effects Health effects that occur randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose without threshold. Hereditary effects and cancer incidence are examples of stochastic effects.

Survey meter Any portable radiation detection instrument especially adapted for inspecting an area to establish the existence and amount of radioactive material present.

Terrestrial Radiation The portion of natural radiation that is emitted by naturally occurring radioactive materials in the Earth.

Thermonuclear An adjective referring to the process in which very high temperatures are used to bring about the fusion of light nuclei.

TLD Thermoluminescent Dosimeter, crystalline materials that emit light if they are heated after having been exposed to radiation.

X-ray- Penetrating electromagnetic radiation (photon) having a wavelength that is much shorter than that of visible light. These rays are usually produced by excitation of the electron field around certain nuclei. In nuclear reactions, it is customary to refer to photons originating in the nucleus as gamma rays, and to those originating in the electron field of the atom as X-rays




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