Can I fuse a Carbon atom into an atom of Hydrogen just as easily as it is done the other way around, or must the smaller-mass atom be the source and the heavier one always be the target?

1 Answer 1


You can fuse atoms in any order, but it's usual to fuse lighter atoms into the target as you'll have a stream of lighter atoms, e.g., Hydrogen with which you are trying to make an heaver atom, e.g., Oxygen.

  • Your answer and reasoning both make sense -- thanks!
    – fbrereto
    Commented Oct 11, 2011 at 22:35
  • Amusingly, the reason it IS commutative is because (at least in Spacechem) fusion merely adds the atomic numbers of the atoms... and addition, of course, is commutative. ChrisF is right, of course, that there are usually practical reasons why you do it one way or the other.
    – lilserf
    Commented Oct 12, 2011 at 20:01

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