RAD
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radiation units
Units of measurement used to express the activity of a radionuclide and the dose of ionizing radiation. The units curie, roentgen, rad, and rem are not coherent with SI units but their temporary use with SI units has been approved while the derived SI units becquerel, gray, and sievert become familiar.
The becquerel (Bq), the SI unit of activity, is the activity of a radionuclide decaying at a rate, on average, of one spontaneous nuclear transition per second. Thus 1 Bq = 1 s−1. The former unit, the curie (Ci), is equal to 3.7 × 1010 Bq. The curie was originally chosen to approximate the activity of 1 gram of radium–226.
The gray (Gy), the SI unit of absorbed dose, is the absorbed dose when the energy per unit mass imparted to matter by ionizing radiation is 1 joule per kilogram. The former unit, the rad (rd), is equal to 10−2 Gy.
The sievert (Sv), the SI unit of dose equivalent, is the dose equivalent when the absorbed dose of ionizing radiation multiplied by the stipulated dimensionless factors is 1 J kg−1. As different types of radiation cause different effects in biological tissue a weighted absorbed dose, called the dose equivalent, is used in which the absorbed dose is modified by multiplying it by dimensionless factors stipulated by the International Commission on Radiological Protection. The former unit of dose equivalent, the rem (originally an acronym for roentgen equivalent man), is equal to 10−2 Sv.
In SI units, exposure to ionizing radiation is expressed in coulombs per kilogram, the quantity of X- or gamma-radiation that produces ion pairs carrying 1 coulomb of charge of either sign in 1 kilogram of pure dry air. The former unit, the roentgen (R), is equal to 2.58 × 10−4 C kg−1.
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(1) (Rapid Application Development) Developing systems incrementally and delivering working pieces every three to four months, rather than waiting until the entire project is programmed before implementing it. Over the years, many information projects have failed, because, by the time the implementation took place, the business had changed.
RAD employs a variety of automated design and development tools, including CASE, 4GLs, visual programming and GUI builders, all of which help create prototypes and running applications faster than by coding program statements a line at a time. The term was coined years ago by industry guru James Martin and focuses on personnel management and user involvement as much as on technology. Joint application development is another RAD concept (see JAD).
The term is also used in a more general way to refer to an environment that produces applications quickly and efficiently.
(2) (RADiation dose) An earlier unit of measurement of absorbed radiation. Defined in the centimeter-gram-second (CGS) system as equal to 100 ergs of energy absorbed by one gram of matter, the rad was superseded by the "gray," an SI unit where 100 rad are equal to one gray. See radiation hardened and gray.
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Oxford Dictionary of Chemistry
A Dictionary of Chemistry. Sixth Edition. Copyright © Market House Books Ltd, 2008. All rights reserved.
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