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radioactivity

[rey-dee-oh-ak-tiv-i-tee] /ˌreɪ di oʊ ækˈtɪv ɪ ti/
noun, Physics, Chemistry
1.
the phenomenon, exhibited by and being a property of certain elements, of spontaneously emitting radiation resulting from changes in the nuclei of atoms of the element.
Also called activity.
Origin
1895-1900
1895-1900; radio- + activity
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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Examples from the web for radioactivity
  • Entering the disaster center was a time-consuming process because of the radioactivity precautions.
  • Back then, radioactivity was new, poorly understood and a hot marketing property.
  • Seafloor reactor sites and surrounding waters are periodically tested for radioactivity levels.
  • radioactivity makes things both simpler and more complex.
  • It loses half of its radioactivity within eight days.
  • Their solution is to mop up the radioactivity in the water with plastic.
  • As atoms change, they emit different levels of radioactivity.
  • Debate promptly began over whether health hazards would be created by the radioactivity it left behind in the upper atmosphere.
  • As with cathode rays and radioactivity a century ago, some false notes are emerging.
  • We're hoping that all of the barriers to release of radioactivity will not fail.
British Dictionary definitions for radioactivity

radioactivity

/ˌreɪdɪəʊækˈtɪvɪtɪ/
noun
1.
the spontaneous emission of radiation from atomic nuclei. The radiation can consist of alpha, beta, and gamma radiation
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for radioactivity
n.

1899, from French radioactivité, coined 1898 by the Curies; see radioactive.

Online Etymology Dictionary, © 2010 Douglas Harper
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radioactivity in Medicine

radioactivity ra·di·o·ac·tiv·i·ty (rā'dē-ō-āk-tĭv'ĭ-tē)
n.

  1. Spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction.

  2. The radiation, including alpha particles, nucleons, electrons, and gamma rays, emitted by a radioactive substance.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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radioactivity in Science
radioactivity
  (rā'dē-ō-āk-tĭv'ĭ-tē)   
The emission of radiation by unstable atomic nuclei undergoing radioactive decay.

Our Living Language  : In the nuclei of stable atoms, such as those of lead, the force binding the protons and neutrons to each other individually is great enough to hold together each nucleus as a whole. In other atoms, especially heavy ones such as those of uranium, this energy is insufficient, and the nuclei are unstable. An unstable nucleus spontaneously emits particles and energy in a process known as radioactive decay. The term radioactivity refers to the particles emitted. When enough particles and energy have been emitted to create a new, stable nucleus (often the nucleus of an entirely different element), radioactivity ceases. Uranium 238, a very unstable element, goes through 18 stages of decay before becoming a stable isotope of lead, lead 206. Some of the intermediate stages include the heavier elements thorium, radium, radon, and polonium. All known elements with atomic numbers greater than 83 (bismuth) are radioactive, and many isotopes of elements with lower atomic numbers are also radioactive. When the nuclei of isotopes that are not naturally radioactive are bombarded with high-energy particles, the result is artificial radioisotopes that decay in the same manner as natural isotopes. Each element remains radioactive for a characteristic length of time, ranging from mere microseconds to billions of years. An element's rate of decay is called its half-life. This refers to the average length of time it takes for half of its nuclei to decay.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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radioactivity in Culture

radioactivity definition


The emission of elementary particles by some atoms when their unstable nuclei disintegrate (see half-life). Materials composed of such atoms are radioactive. (See alpha radiation, beta radiation, and gamma radiation.)

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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