<P> The triple - alpha process is a set of nuclear fusion reactions by which three helium - 4 nuclei (alpha particles) are transformed into carbon . </P> <P> Helium accumulates in the core of stars as a result of the proton--proton chain reaction and the carbon--nitrogen--oxygen cycle . Further nuclear fusion reactions of helium with hydrogen or another alpha particle produce lithium - 5 and beryllium - 8 respectively . Both products are highly unstable and decay, almost instantly, back into smaller nuclei, unless a third alpha particle fuses with a beryllium before that time to produce a stable carbon - 12 nucleus . </P> <P> When a star runs out of hydrogen to fuse in its core, it begins to collapse until the central temperature rises to 10 K, six times hotter than the sun's core . At this temperature and density, alpha particles can fuse fast enough (the half - life of Li is 6978370000000000000 ♠ 3.7 × 10 s and that of Be is 6983670000000000000 ♠ 6.7 × 10 s) to produce significant amounts of carbon and restore thermodynamic equilibrium in the core </P>

What are the products of helium burning in a star