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Glossary of Radiation Terms

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Glossary of Radiation Terms GLOSSARY – Nagasaki University Center for Frontier Life Sciences GLOSSARY OF expressed by the linear absorption RADIATION TERMS coefficient. ACCELERATOR (PARTICLE): A device that accelerates charged sub-atomic ABSOLUTE RISK: The rate of disease particles to very great energies. These among a population. particles may be used for basic physics research, radioisotope production or for ABSORBED DOSE, D: The fundamental direct medical irradiation of patients. dose quantity given by the mean energy imparted to matter of mass by ionizing ACTIVATION: Absorption, usually of radiation. The SI unit for absorbed dose is neutrons or charged particles (the minimum joule per kilogram (J kg-1) and its special energy to induce this effect is 10 MeV) by name is gray (Gy). 1 Gy = 1 J/kg = 100 nuclei thereby making them radioactive. rads. ACTIVE (RED) BONE MARROW: The ABSORBED DOSE, MEAN IN A TISSUE organ system bone marrow contains the OR ORGAN, DT: The absorbed dose DT, cell systems for the formation of blood cells averaged over the tissue or organ T, which starting from the pluripotent haematopietic is given by stem cells to the mature blood cells. ACTIVITY, A: Is the number of nuclear where εT is the mean total energy imparted transformations occurring in a given in a tissue or organ T, and mT is the mass quantity of material per unit time. The SI of that tissue or organ. unit for the transformation rate is the Becquerel (Bq), which is defined as one ABSORPTION: Transfer or deposition of disintegration per second. 1 Bq = 2.7 x some or all of the energy of radiation 10-11Ci. 1 Ci = 3.7 x 1010Bq. traversing matter. ACUTE RADIATION SYNDROME (ARS): ABSORPTION COEFFICIENT: Since the A serious illness caused by receiving a absorption of gamma or X-rays is dose greater than 75 rads of penetrating exponential in nature, these radiations radiation to the body in a short time (usually have no clear cut range. The fractional minutes). The earliest symptoms are decrease in the intensity of such a beam nausea, fatigue, vomiting, and diarrhea. per unit thickness of the absorber is 1 GLOSSARY – Nagasaki University Center for Frontier Life Sciences Hair loss, bleeding, swelling of the mouth ANNUAL LIMIT ON INTAKE (ALI): The and throat, and general loss of energy may activity of a radionuclide which, upon follow. If the exposure has been ingestion, results in an exposure equal to approximately 1,000 rads or more, death the annual maximum permissible dose. may occur within 2 – 4 weeks. APOPTOSIS: An active biochemical ADAPTIVE RESPONSE: A post-irradiation process of programmed cell death following cellular response which, typically, serves to radiation or other insults. increase the resistance of the cell to a subsequent radiation exposure. ATOM: A particle of matter indivisible by chemical means. It is the fundamental ALPHA PARTICLE: A positively charged building block of elements. highly energetic nuclear fragment, comprised of two neutrons and two protons ATOMIC ENERGY BASIC LOW: The (helium nucleus). Japanese Law established in 1955, which declares the use of atomic energy only for AMBIENT DOSE EQUIVALENT, H*(10): peaceful aim through democratic The dose equivalent at a point in a administration, autonomous radiation field that would be produced by accomplishment and results disclosure in the corresponding expanded and aligned the public. field in the ICRU sphere at a depth of 10 mm on the radius vector opposing the ATOMIC NUMBER: The number assigned direction of the aligned field. The unit of to each element on the basis of the number ambient dose equivalent is joule per of protons found in the element's nucleus. kilogram (J kg-1) and its special name is sievert (Sv). ATOMIC WEIGHT (ATOMIC MASS): Approximately the sum of the number of ANION: A negatively charged ion. protons and neutrons found in the nucleus of an atom. ANNIHILATION RADIATION: Positrons interact with negative electrons resulting in ATTENUATION: The reduction of the the disappearance of both particles and the intensity of a beam of gamma or x-rays as it release of two annihilation 511 keV passes through some material. Beam photons. energy can be lost by deposition (absorption) and/or by deflection (deflection 2 GLOSSARY – Nagasaki University Center for Frontier Life Sciences attenuation). The three primary defined as one nuclear disintegration per mechanisms by which energy is transferred second (dps). 1 Bq = 2.7 x 10-11Ci. 1 Ci = from the beam to the material through 3.7 x 1010Bq. which it passes are the photoelectric effect, the Compton effect and pair production. BETA PARTICLE: Negatively charged particle emitted from the nucleus of an ATTRIBUTABLE RISK: The estimated rate atom. It is just an energetic electron. of a disease (such as lung cancer) that could, in theory, prevented if all exposures BIAS: Factors that influence the outcome to a particular causative agent (such as of data collection, such as causing certain radon) were eliminated. measurements to have a greater chance of being included than others. AVERTED DOSE: The dose prevented or avoided by the application of a protective BINDING ENERGY: The minimum energy measure or set of protective measures, i.e., required to separate a nucleus into its the difference between the projected dose component neutrons and protons. if the protective measure(s) had not been applied and the expected residual dose. BIOASSAY: Any procedure used to determine the nature, activity, location, or BACKGROUND RADIATION: The retention of radionuclides in the body by in radiation to which a member of the vivo measurement or by in vitro analysis of population is exposed from natural sources, material excreted or otherwise removed such as terrestrial radiation due to naturally from the body. occurring radionuclides in the soil, cosmic radiation originating in outer space, and BOHR RADIUS: The size of a ground state naturally occurring radionuclides in the hydrogen atom as calculated by Niels Bohr human body. using a mix of classical physics and quantum mechanics. BEAM: A flow of electromagnetic or particulate radiation that is generally BRACHYTHERAPY: Radiation treatment unidirectional or is divergent from a of a patient using sealed or unsealed radioactive source but is confined to a sources of radiation placed within the small angle. patient’s body. BECQUEREL (Bq): The SI unit of activity BRANCHING: The occurrence of two or 3 GLOSSARY – Nagasaki University Center for Frontier Life Sciences more modes by which a radionuclide can undergo radioactive decay to the ultimate CASE-CONTROL STUDY: An stable state. An individual atom of a nuclide epidemiologic study in which people with exhibiting branching disintegrates by one disease and a similarly composed control mode only. The fraction disintegrating by a group are compared in terms of exposures particular mode is the branching fraction for to a putative causative agent. that mode. The branching ratio is the ratio of two specified branching fractions (also CHARACTERISTIC X-RAY: A collision of called multiple disintegration). the fast-moving electrons with the atom first causes a tightly bound inner-shell electron BREMSSTRAHLUNG: Secondary to be ejected from the atom; a loosely electromagnetic radiations produced by the bound outer-shell electron then falls into rapid deceleration of charged particles in the inner shell to fill the vacancy. In the strong electromagnetic fields. The process, a single photon (characteristic likelihood of emission is proportional to the X-ray) is emitted by the atom with an mass of the nucleus of the absorber. energy equal to the difference between the inner-shell and outer-shell vacancy states. BYSTANDER EFFECT: A response in unirradiated cells that is triggered by COHORT STUDY: An epidemiologic study signals received from irradiated in which groups of people (the cohort) are neighbouring cells. identified with respect to the presence or absence of exposure to a disease-causing CARRIER: A quantity of non-radioactive or agent, and in which the outcomes of non-labeled material of the same chemical disease rates are compared; also called a composition as its corresponding follow-up study. radioactive or labeled counterpart. COLLECTIVE DOSE: The estimated dose CARRIER-FREE: A preparation of for an area or region multiplied by the radioisotope to which no carrier has been estimated population in that area or region. added and for which precautions have been taken to minimize contamination with COMMITTED DOSE EQUIVALENT: The other isotopes. Material of high specific total dose equivalent averaged throughout activity is often loosely referred to as a tissue 50 years after body uptake of the "carrier-free" but is more correctly defined radionuclide. as "high isotopic abundance". 4 GLOSSARY – Nagasaki University Center for Frontier Life Sciences COMPTON EFFECT: Interactive effect of excess energy of unstable nucleus to one X-ray and gamma radiation with matter. of its own orbiting electrons. The Compton effect is the elastic scattering of a quantum with a free or quasi-free COSMIC RADIATION: Radiation produced electron from the electron sheath of an in outer space when heavy particles from atom. Part of the energy and the pulse of other galaxies (nuclei of all known natural the quantum is transferred to the electron, elements) bombard the earth. the rest remains with the scattered quantum. COULOMB (C): The quantity of electricity transported in one second by a current of CONFIDENCE LIMITS: An interval giving one ampere. the lowest and highest estimate of a parameter that is statistically compatible COUNTER: A general designation applied with the data. For a 95% confidence to radiation detection instruments or survey interval, there is a 95% chance that the meters that detect and measure radiation. interval contains the parameter. The signal that indicates an ionization event has been detected is called a count. CONTAMINATION, RADIOACTIVE: Unwanted deposition of radioactive COUNTER, SCINTILLATION: Scintillation material in or on any medium or surface.
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