Alpha reactions
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The alpha reactions is one of two class of fusion reactionss by which stars convert helium into heavier elements, the other being the triple-alpha process. In contrast with the triple-alpha process which only require helium to occur, once some carbon is produced, other reactions that consume helium are possible:

12C + 4He	→	16O + γ
16O + 4He	→	20Ne + γ
20Ne+ 4He	↔	44Mg + γ

All these reactions have a very low rate and therefore do not contribute significantly to the energy production in stars; with elements heavier than Neon (atomic number > 20) they occur even less easily due to the increasing Coulomb barrier.

The original article can be found at: http://en.wikipedia.org/wiki/Alpha_reactions.
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