Neon burning process is a set of nuclear fusion reactions that take place in massive stars (at least 8 MSun). Neon burning requires high temperatures and densities (around 1.2×109 K and 4×109 kg/m3).
At such high temperatures photodisintegration is important, so some neon nuclei decompose releasing alpha particles
- 20Ne + γ → 16O + 4He
These alpha particles can be recycled to produce magnesium-24
- 20Ne + 4He → 24Mg + γ
Alternatively
- 20Ne(n,γ)21Ne(4He,n)24Mg
where the neutron produced in the second step can be recyled in the first.
Neon burning takes place after carbon burning have consumed all carbon in the core and built up a new Oxygen-Neon-Magnesium core. The core cools down, gravitation compreses it increasing densitiy and temperature up to the ignition point of Neon burning.
During neon burning, Oxygen and magnesium accumulates in the central core while neon is consumed. After a few years the star consumes all its neon and the core cools down again. Gravitational pressure takes over and compress the central core, increasing its density and temperature until oxygen burning process can start.