Synthesis of noble metals
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Synthesis of noble metals refers to the realization of the age-old dream of alchemists—to artificially produce noble metals. The goal of this could be to achieve greater economic gain when compared to traditional methods of obtaining noble metals. Synthesis of noble metals is only possible with methods of nuclear physics, either using nuclear reactors or by particle accelerators. Particle accelerators require huge amounts of energy, while nuclear reactors produce energy, so only production methods utilizing a nuclear reactor are of economic interest.
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[edit] Rhodium, Ruthenium
Rhodium and ruthenium are noble metals produced by nuclear fission, as a small percentage of the fission products. The radio-isotopes of these elements with the longest half-life, which are generated by nuclear fission have half-life times of 45 days and 373.59 days for rhodium and ruthenium, respectively. This makes their extraction from spent nuclear fuel possible, although they must be checked for radioactivity before leaving the control range.
Until now no facility has been reprocessing spent nuclear fuels for rhodium and ruthenium; however Japan is planning to do so in their new spent fuel reprocessing facility, which will help offset the cost of reprocessing.
[edit] Palladium
Palladium is also produced by nuclear fission in small percentages, amounting to 1 kg per ton of spent fuel. As opposed to rhodium and ruthenium, palladium has a radioactive isotope, 107Pd, with a very long half-life time of 6.5 million years, so palladium produced in this way has a very low radioactive intensity. Mixed in with the other isotopes of palladium recovered from the spent fuel, this gives a radioactive dose rate of 7.207x10-5 Ci, which is well below the safe level of 1x10-3 Ci.
[edit] Gold
The artificial production of gold is the age-old dream of the alchemists. It is possible in particle accelerators or nuclear reactors. Since there is only one stable gold isotope, Au-197, nuclear reactions must create this isotope in order to produce usable gold.
[edit] Gold synthesis from Mercury
Gold obtained by mining has copper and silver as impurities. Gold of higher purity can be made through the photoneutron process:
Mercury198 + 6.8Mev gamma ray > 1neutron + Mercury197 (half-life 2.7 days > Gold 197)
These energy levels allow a more efficient neutron source than the Spallation Neutron Source.
[edit] Gold synthesis in an accelerator
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.
[edit] Gold synthesis in a nuclear reactor
In a nuclear reactor, gold can be manufactured by irradiation of platinum or mercury. Since platinum is more expensive than gold, platinum is economically unsuitable as a raw material. Only the mercury isotope Hg-196, which occurs with a frequency of 0.15% in natural mercury, can be converted to gold by neutron capture, and following K+- decay into Au-197 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 Hg-198, which is contained to 9.97% in natural mercury, can be converted by splitting off a neutron and becoming Hg-197, 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 get the Hg-197. However such high-energy neutrons can be produced only by particle accelerators.
[edit] Silver
Silver is produced as result of nuclear fission in small amounts (approximately 0.1 %). Because of this, extraction of silver from highly radioactive fission products would be uneconomical, but when recovered with palladium, rhodium and ruthenium (price of silver in 2005: about 200 €/kg, rhodium and ruthenium: about 300,000 €/kg) the economics change substantially. Silver becomes a byproduct of platinoid metal recovery from fission waste.
