The main nuclear reactions during helium combustion are:
4He+4He=8Be
8Be+4He=12C*→12C+γ
8Be is unstable and emits alpha particles (t1/2 ≈ 2 * 10-16s). It is only 0.094MeV more stable than the helium core that makes up it. When it reaches the core of the red giant, the calculated balance ratio of 8Be to 4He is about 10-9. Although the number is small, other ways can be used to make the impossible three body collision happen. F. Hoyle predicted that the energy of 12C * is 7.70 MeV higher than that of 12C, about 7.653 MeV higher than that observed in experiments three years later. He also pointed out that the energy difference Q (12C * - 34He) is 0.373 MeV, and the total reaction energy is:
34He→12c+γ Q=27.148MeV
Then further helium combustion reaction occurs to synthesize some important nuclei:
12C+4He→16O+γ Q=27.148MeV
16O+4He→20Ne+γ Q=4.74MeV
20Ne+4He→24Mg+γ Q=9.31MeV
These reactions consume the helium produced by hydrogen combustion, and develop into a core composed of carbon, oxygen and neon, and finally generate heat by gravitational contraction.
