The alpha reactions is one of two class of fusion reactionss by which stars convert helium into heavier elements, the other being the triple-alpha process.
In contrast with the triple-alpha process which only require helium to occur, once some carbon is produced, other reactions that consume helium are possible:
12C + 4He
→
16O + γ
16O + 4He
→
20Ne + γ
20Ne+ 4He
↔
44Mg + γ
All these reactions have a very low rate and therefore do not contribute significantly to the energy production in stars;
with elements heavier than Neon (atomic number > 20) they occur even less easily due to the increasing Coulomb barrier.
