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.
what are the products of helium burning in a star
carbon - 12