Since there is only one stable gold isotope, 197Au, nuclear reactions must create this isotope in order to produce usable gold.
Gold synthesis in a particle accelerator is possible in many ways. The Spallation Neutron Source has a liquid mercury target that will be transmuted into gold, platinum, and iridium, which are lower in atomic number.
Gold was first synthesized from mercury by neutron bombardment in 1941, but the isotopes of gold produced were all radioactive.
Gold can currently be manufactured in a nuclear reactor by irradiation either of platinum or mercury.
Only the mercury isotope 196Hg, which occurs with a frequency of 0.15% in natural mercury, can be converted to gold by neutron capture, and following electron capture-decay into 197Au with slow neutrons. Other mercury isotopes are converted when irradiated with slow neutrons into one another or formed mercury isotopes, which beta decay into thallium.
Using fast neutrons, the mercury isotope 198Hg, which composes 9.97% of natural mercury, can be converted by splitting off a neutron and becoming 197Hg, which then disintegrates to stable gold. This reaction, however, possesses a smaller activation cross-section and is feasible only with un-moderated reactors.
It is also possible to eject several neutrons with very high energy into the other mercury isotopes in order to form 197Hg. However such high-energy neutrons can be produced only by particle accelerators