carbon-nitrogen cycle

Medical Dictionary

carbon-nitrogen cycle n.
A chain of thermonuclear reactions in which nitrogen isotopes are formed in intermediate stages and carbon acts essentially as a catalyst to convert four hydrogen atoms into one helium atom with the emission of two positrons. The entire sequence is thought to generate significant amounts of energy in the sun and certain other stars. Also called carbon cycle, nitrogen cycle.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
carbon-nitrogen cycle  
See carbon cycle.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

carbon-nitrogen cycle

sequence of thermonuclear reactions that provides most of the energy radiated by the hotter stars. It is only a minor source of energy for the Sun and does not operate at all in very cool stars. Four hydrogen nuclei are in effect converted into one helium nucleus, a fraction of the mass being released as energy (according to the law of mass-energy equivalence, E = mc2). The German-U.S. physicist Hans Bethe, in 1938, first described the process.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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