Marathon Fusion says it has turned mercury into gold with fusion neutrons, 10x CERN's record
What happened? San Francisco fusion startup Marathon Fusion says it has turned mercury into real, stable gold using neutrons from fusion reactions, at a rate it claims is ten times the record set at CERN in 2025. "We've reduced alchemy to a series of difficult but tractable engineering problems," the company wrote on X on 21 October. It shared gamma-ray spectra showing the signatures of mercury-197 and gold-197 after irradiation, and said it had also produced copper-64 and copper-67, isotopes used in cancer imaging and targeted radiotherapy, by irradiating zinc.
How does it work? Fast 14 MeV neutrons from deuterium-tritium fusion knock a neutron out of mercury-198, an abundant stable isotope, turning it into radioactive mercury-197, which decays into stable gold-197. In a 2025 paper Marathon modelled a fusion power plant blanket that could produce about 2 tonnes of gold per gigawatt of thermal power each year without hurting electricity output or tritium breeding, arguing gold sales could roughly double a plant's revenue.
The caveats: Marathon has not disclosed how much gold it actually made, and the result has not been independently validated. For scale, CERN's ALICE experiment produced about 29 picograms of gold over four years of LHC running. The company's paper also notes that freshly transmuted gold would carry radioactive isotopes and need years of storage before sale, and its current reactor is rated at around 1 kW of fusion power, a millionth of a gigawatt. Global mines produced about 3,670 tonnes of gold in 2025, so any effect on the gold price is far off.
The bigger picture: The post went viral, with investors asking whether lab-grown gold could do to gold what lab-grown diamonds did to diamonds. The more immediate business is medical isotopes and fusion components: Marathon is looking for revenue from neutrons long before fusion electricity is commercial. It is now building a reactor in San Francisco aimed at record power density. Marathon started out in 2023 building fuel-processing systems for fusion plants and raised a $5.9 million seed round in 2024 led by the 1517 Fund and Anglo American.
Read more: Marathon Fusion on X · Marathon Fusion: Alchemy · Business Today · BeInCrypto
