B Question about Neon-burning Process

[DrLich]

During the neon-burning process in stars, why do two Neon-20 atoms fuse into Oxygen-16 and Magnesium-24 instead of forming Calcium-40?

 

[Bandersnatch]

The 2Ne20->O16+Mg24+energy reaction is the nett result. It's actually two reactions.
First, neon is photodisintegrated into oxygen and an alpha particle:
Ne20+gamma->O16+He4
Normally the reverse reaction would occur, keeping the neon stock steady. But with sufficient temperature, alpha capture by another neon nucleus is preferred:
Ne20+He4->Mg24+gamma
So you need two neon nuclei, one to donate the alpha particle, the other to subsequently absorb it. It's not that the two neons collide, and two other nuclei pop out.

See e.g. here:
https://iopscience.iop.org/article/10.1088/0004-637X/797/2/83

 

[DrLich]

The 2Ne20->O16+Mg24+energy reaction is the nett result. It's actually two reactions.
First, neon is photodisintegrated into oxygen and an alpha particle:
Ne20+gamma->O16+He4
Normally the reverse reaction would occur, keeping the neon stock steady. But with sufficient temperature, alpha capture by another neon nucleus is preferred:
Ne20+He4->Mg24+gamma
So you need two neon nuclei, one to donate the alpha particle, the other to subsequently absorb it. It's not that the two neons collide, and two other nuclei pop out.

See e.g. here:
https://iopscience.iop.org/article/10.1088/0004-637X/797/2/83

Thank you very much!