8. The Machinery Behind The      Periodic Table   Previous PageNext Page
     Postscript: The Making of a Universe

At even higher temperatures, higher than can be reached in our sun, further buildup is possible. Carbon and oxygen begin to fuse at 500 - 1000 million degrees. One of the main products of carbon and oxygen fusion is silicon-28, which has a particularly stable nucleus. As temperatures increase to 2000 million degrees and more, silicon itself begins to react by a complicated set of fusion processes:

Only if a star is big enough to trap heat in its interior and generate these enormous temperatures will these reactions occur.

The energy in these reactions comes from a loss of mass during the fusion process. One helium nucleus is lighter than four hydrogen nuclei, and an oxygen nucleus is lighter than the sum of a carbon nucleus and a helium nucleus. The missing mass is converted to energy, according to Einstein's conversion formula, E = m c .

These reactions cannot continue building up heavier atoms indefinitely. The process stops with iron, 56Fe. The iron nucleus is the most stable of all. Energy is given off whenever nuclei lighter than iron fuse to produce elements closer to iron, or when heavier nuclei, such as uranium, produce lighter elements near to iron by fission.

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