The triple-α process and the origin of the elements
The triple-α process is the nuclear fusion of helium to carbon. Two 4 He nuclei collide and form an unstable state of 8 Be. Before this can decay back a third α-particle collides with it to form a 12 C nucleus. The reaction rate is probably the most temperature sensitive known to physics because there is a resonant state of the 12 C nucleus at just the energy of the 8 Be* and the 4 He that have the greatest chance of penetrating the Coulomb barrier. The reaction takes place in stars that have exhausted their central hydrogen fuel. Most interesting are the asymptotic giants that can dredge the carbon produced to the surface and return it, perhaps first processing it to nitrogen, to the interstellar medium. The fortuitous energy of the resonant state of 12 C and its consequences are crucial to the way stars evolve and the abundance of carbon on the Earth.
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Document Type: Research Article
Affiliations: Centre for Stellar and Planetary Astrophysics, School of Mathematics, Monash University, Victoria, 3800, Australia
Publication date: 2006-05-01