Ruthenium

Each kilogram of the fission products of ²³⁵U will contain 63.44 grams of ruthenium isotopes with halflives longer than a day. Since a typical used nuclear fuel contains about 3% fission products, one ton of used fuel will contain about 1.9 kg of ruthenium. The ¹⁰³Ru and ¹⁰⁶Ru will render the fission ruthenium very radioactive. If the fission occurs in an instant then the ruthenium thus formed will have an activity due to ¹⁰³Ru of 109 TBq g⁻¹ and ¹⁰⁶Ru of 1.52 TBq g⁻¹. ¹⁰³Ru has a half-life of about 39 days meaning that within 390 days it will have effectively decayed to the only stable isotope of rhodium, ¹⁰³Rh, well before any reprocessing is likely to occur. ¹⁰⁶Ru has a half-life of about 373 days, meaning that if the fuel is left to cool for 5 years before reprocessing only about 3% of the original quantity will remain; the rest will have decayed.^[1] To put the values in the table into perspective, the activity in natural potassium (due to naturally occurring ⁴⁰
K) is about 30 Bq per gram.

Rhodium

It is possible to extract rhodium from used nuclear fuel: 1 kg of fission products of ²³⁵U contains 13.3 grams of ¹⁰³Rh. At 3% fission products by weight, one ton of used fuel will contain about 400 grams of rhodium. The longest lived radioisotope of rhodium is ^102mRh with a half-life of 2.9 years, while the ground state (¹⁰²Rh) has a half-life of 207 days.^[1]

Each kilogram of fission rhodium will contain 6.62 ng of ¹⁰²Rh and 3.68 ng of ^102mRh. As ¹⁰²Rh decays by beta decay to either ¹⁰²Ru (80%) (some positron emission will occur) or ¹⁰²Pd (20%) (some gamma ray photons with about 500 keV are generated) and the excited state decays by beta decay (electron capture) to ¹⁰²Ru (some gamma ray photons with about 1 MeV are generated). If the fission occurs in an instant then 13.3 grams of rhodium will contain 67.1 MBq (1.81 mCi) of ¹⁰²Rh and 10.8 MBq (291 μCi) of ^102mRh. As it is normal to allow used nuclear fuel to stand for about five years before reprocessing, much of this activity will decay away leaving 4.7 MBq of ¹⁰²Rh and 5.0 MBq of ^102mRh. If the rhodium metal was then left for 20 years after fission, the 13.3 grams of rhodium metal would contain 1.3 kBq of ¹⁰²Rh and 500 kBq of ^102mRh. Rhodium has the highest price of these precious metals ($440,000/kg in 2022^[2]), but the cost of the separation of the rhodium from the other metals needs to be considered, although recent high prices may create opportunity for consideration.^[1]

Gold

Chrysopoeia, the artificial production of gold, is the traditional goal of alchemy. Such transmutation is possible in particle accelerators or nuclear reactors, although the production cost is currently many times the market price of gold. Since there is only one stable gold isotope, ¹⁹⁷Au, nuclear reactions must create this isotope in order to produce usable gold.

Gold was synthesized from mercury by neutron bombardment in 1941, but the isotopes of gold produced were all radioactive.^[3] In 1924, a German scientist, Adolf Miethe, reported achieving the same feat, but after various replication attempts around the world, it was deemed an experimental error.^[4][5][6]

In 1980, Glenn Seaborg transmuted several thousand atoms of bismuth into gold at the Lawrence Berkeley Laboratory. His experimental technique was able to remove protons and neutrons from the bismuth atoms. Seaborg's technique was far too expensive to enable the routine manufacture of gold but his work is the closest yet to emulating an aspect of the mythical Philosopher's Stone.^[7][8]