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nuclear reaction

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Nuclear Reaction
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Nuclear Reaction
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re⋅ac⋅tion

  [ree-ak-shuhn]
–noun
1. a reverse movement or tendency; an action in a reverse direction or manner.
2. movement in the direction of political conservatism or extreme rightism.
3. action in response to some influence, event, etc.: the nation's reaction to the President's speech.
4. Physiology. action in response to a stimulus, as of the system or of a nerve, muscle, etc.
5. Medicine/Medical.
a. the action caused by the resistance to another action.
b. a return to the opposite physical condition, as after shock, exhaustion, or chill.
6. Bacteriology, Immunology. the specific cellular response to foreign matter, as in testing for allergies.
7. Chemistry. the reciprocal action of chemical agents upon each other; chemical change.
8. Also called nuclear reaction. Physics. a process in which a nucleus that is bombarded by a photon, particle, or other nucleus, emits a nucleon, alpha particle, or the like, without a significant change in its atomic weight.
9. Mechanics. the instantaneous response of a system to an applied force, manifested as the exertion of a force equal in magnitude but opposite in direction to the applied force.
10. Commerce. a decline in the market after an advance in prices.
Origin:
1635–45; re- + action, modeled on react

Related forms:
re⋅ac⋅tion⋅al, adjective
re⋅ac⋅tion⋅al⋅ly, adverb
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.
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nuclear reaction  
n.  A reaction, as in fission, fusion, or radioactive decay, that alters the energy, composition, or structure of an atomic nucleus.
The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Cultural Dictionary

nuclear reaction

A reaction that changes the number of protons or neutrons in the nucleus of an atom. There are several kinds of nuclear reactions, including the fragmentation of large nuclei into smaller ones (nuclear fission), the building up of small nuclei into larger ones (nuclear fusion), and changes begun by collisions with elementary particles or other nuclei (as in particle accelerators).

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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Word Origin & History

reaction 
1611, from re- "again, anew" + action (q.v.). Modeled on Fr. réaction, older It. reattione, from M.L. reactionem (nom. reactio), from L.L. react-, pp. stem of reagere "react," from re- "back" + agere "to do, act" (see act). Originally scientific; physiological sense is attested from 1805; psychological sense first recorded 1887; general sense of "action or feeling in response" (to a statement, event, etc.) is recorded from 1914. The verb react is attested from 1644.
Online Etymology Dictionary, © 2001 Douglas Harper
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Financial Dictionary

reaction

A decline in security prices following a period of rising security prices.

Wall Street Words: An A to Z Guide to Investment Terms by David L. Scott.
Copyright © 2003. Published by Houghton Mifflin.
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Medical Dictionary

Main Entry: re·ac·tion
Pronunciation: rE-'ak-sh&n
Function: noun
1 : the act or process or an instance of reacting
2 : bodily response to or activity aroused by a stimulus: a : an action induced by vital resistance to another action; especially : the response of tissues to aforeign substance (as an antigen or infective agent) b : depression or exhaustion due to excessive exertion or stimulation c : abnormally heightened activitysucceeding depression or shock d : a mental or emotional disorder forming an individual's response to his or her life situation
3 : the force that a body subjectedto the action of a force from another body exerts in the opposite direction
4 a (1) : chemical transformation or change : the interaction of chemical entities (2) : the state resulting from such a reaction b : a process involving change in atomic nuclei
Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.
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Medical Dictionary

reaction re·ac·tion (rē-āk'shən)
n.

  1. A response of an organism or living tissue to a stimulus.

  2. The state resulting from such a response.

  3. A chemical change or transformation in which a substance decomposes, combines with other substances, or interchanges constituents with other substances.

  4. The response of cells or tissues to an antigen, as in a test for immunization.

  5. A pattern of behavior constituting a mental disorder or personality type.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Science Dictionary
nuclear reaction  
A process, such as fission, fusion, or radioactive decay, in which the structure of an atomic nucleus is altered through release of energy or mass or by being broken apart. See more at fission, fusion.
reaction   (rē-āk'shən)  Pronunciation Key 

  1. A rearrangement of the atoms or molecules of two or more substances that come into contact with each other, resulting in the formation of one or more new substances. Chemical reactions are caused by electrons of one substance interacting with those of another. The reaction of an acid with a base, for example, results in the creation of a salt and water. Some, but not all, reactions can be reversed.

  2. See nuclear reaction.

  3. An action that results directly from or counteracts another action, especially the change in a body's motion as a result of a force applied to it. Some reactions counteract forces and are not readily apparent. When an object rests on a surface, such as a table, for example, the downward force it applies to the surface is counteracted by an equal but upwards force, or reaction, applied by the surface. See more at Newton's laws of motion.

  4. A response to a stimulus, such as a reflex.

  5. The response of cells or tissues to an antigen, as in a test for immunization.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia

nuclear reaction

change in the identity or characteristics of an atomic nucleus, induced by bombarding it with an energetic particle. The bombarding particle may be an alpha particle, a gamma-ray photon, a neutron, a proton, or a heavy ion. In any case, the bombarding particle must have enough energy to approach the positively charged nucleus to within range of the strong nuclear force.

Learn more about nuclear reaction with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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