What is triple fusion, where and how does it take place, name the nuclei involved?

Triple fusion (or triple alpha process) is the nuclear fusion reaction in stars where three helium-4 nuclei (alpha particles) fuse to form one carbon-12 nucleus. It takes place in the core of stars when helium is abundant and temperature and pressure are high.

• Where it takes place: In the core of stars during the helium-burning phase. After hydrogen fusion has built up helium, at high temperatures (~10⁸ K) and densities the triple-alpha process begins.
• How it takes place & nuclei involved:
  • Two helium-4 nuclei (2 × ⁴He) fuse to form unstable beryllium-8 (⁸Be). Because ⁸Be is unstable it decays quickly unless another ⁴He collides almost immediately.
  • Then a third ⁴He nucleus collides with the ⁸Be, forming ¹²C (carbon-12) in an excited state, then releases energy and settles to stable carbon-12. Reaction: 3 ⁴He → ¹²C + energy.
• This process is crucial for stellar nucleosynthesis of carbon, an element essential for life.