Iron

How to play: Use your arrow keys to move the tiles. When two tiles that can fuse touch, they do! For a list of reactions, see Reactions below, and Physics Comments for commentary.

Proton-Proton Chain

p + p → D (15%)

D + p → ³He

³He + ³He → ⁴He + p + p

Triple-alpha

⁴He + ⁴He → ⁸Be

⁸Be + ⁴He → ¹²C

CNO cycle

p + ¹²C → ¹³C (after β decay)

p + ¹³C → ¹⁴N

p + ¹⁴N → ¹⁵N (after β decay)

p + ¹⁵N → ¹²C + ⁴He

Alpha burning

¹²C + ⁴He → ¹⁶O

¹⁶O + ⁴He → ²⁰Ne

²⁰Ne + ⁴He → ²⁴Mg

²⁴Mg + ⁴He → ²⁸Si

²⁸Si + ⁴He → ³²S

³²S + ⁴He → ³⁶Ar

³⁶Ar + ⁴He → ⁴⁰Ca

⁴⁰Ca + ⁴He → ⁴⁴Ti

⁴⁴Ti + ⁴He → ⁴⁸Cr

⁴⁸Cr + ⁴He → ⁵²Fe

⁵²Fe + ⁴He → ⁵⁶Fe (after β decays!)

Carbon and Oxygen burning

¹²C + ¹²C → ²⁰Ne + ⁴He

¹⁶O + ¹⁶O → ²⁸Si + ⁴He

Currently implemented are the proton-proton I chain, triple-alpha process, CNO-I process, alpha-burning (alpha-ladder) process, Carbon burning, and Oxygen burning.
Note that the last step of the alpha ladder actually produces 56Ni, which subsequently decays to 56Fe! There are other steps (such as in CNO) that also involve β decays. This is an incomplete but hopefully fun overview of nucleosynthesis!