What fundamental difference exists between the creation of iron via fusion and the creation of gold during a supernova?

Iron is made by fusion that releases net energy (up to the peak), whereas gold is made by rapid capture of free neutrons in a non-equilibrium environment.

The creation mechanisms for iron and elements heavier than iron, such as gold, are fundamentally distinct, even though both occur within the context of a massive star's death. Iron is the final product of stellar fusion, where combining lighter elements releases the maximum net energy the star can harness to support itself against gravity. In contrast, elements heavier than iron are forged *after* the iron core collapses. Their creation relies on the r-process (rapid neutron capture), where atomic nuclei absorb a high flux of free neutrons in the explosive, non-equilibrium environment of the supernova shockwave. This process of neutron capture generates heavy elements but is explicitly noted as *not* being a fusion process that generates energy.