San Francisco startup Marathon Fusion claims it converted mercury into stable gold using fusion-generated neutrons. The company said it surpassed a 2025 CERN record by a factor of 10. While the process uses nuclear transmutation, the firm kept the total gold amount secret, leaving many experts questioning its commercial potential.
Marathon Fusion, a San Francisco-based startup, claims to have converted mercury into stable gold using fusion-generated neutrons, at a rate it says is 10 times the record set by CERN in 2025. The company has not disclosed how much gold its experiment produced, leaving the scale and commercial potential of the claimed breakthrough unclear.
In a post on X that garnered 6.5 million impressions, the company said it had demonstrated high-rate alchemy by turning mercury into real, stable gold, surpassing CERN's record by a factor of 10.
The claim has renewed interest in a question that has intrigued alchemists for centuries: whether gold can be manufactured artificially. However, Marathon Fusion's broader ambitions extend beyond gold production.
The company is developing technology aimed at producing scarce medical isotopes for cancer diagnosis and treatment, while building the engineering capabilities required for future fusion power plants.
How does the process work?
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The technique, known as nuclear transmutation, involves changing an atom's nucleus to produce a different element or isotope. Unlike chemical reactions, which rearrange atoms without altering their nuclei, nuclear transmutation changes the composition of the nucleus itself.
Marathon Fusion's proposed process starts with mercury-198, a stable, naturally occurring isotope of mercury. Fusion-generated neutrons trigger a nuclear reaction that converts mercury-198 into mercury-197. The mercury-197 then decays into gold-197, a stable isotope of gold. However, radioactive byproducts generated during the process remain a challenge.
The underlying nuclear physics is established. In May 2025, researchers at CERN's Large Hadron Collider reported producing gold nuclei through collisions involving lead nuclei.
Isotope separation and medical applications
Marathon Fusion has also reported progress in isotope separation, claiming it has selectively compressed isotopes using a plasma centrifuge. According to the company, this work surpassed a Soviet-era record that had stood for 40 years.
In a separate development, the startup said it had begun producing radioactive copper isotopes by irradiating zinc with fusion-generated neutrons. The company has presented these developments as part of its broader effort to develop fusion technology for industrial applications.
However, key details of the gold experiment remain undisclosed. Marathon Fusion has not revealed the quantity of gold produced or its production cost. The information released so far is also insufficient to establish the purity of the resulting material or determine whether the process can be scaled commercially.
Ambitious targets for fusion technology
Marathon Fusion is developing a fusion reactor designed to generate neutrons at rates and concentrations suitable for specialised industrial applications, including medical isotope production.
The company has outlined a target of directing a trillion neutrons every second at a target measuring just one centimetre across, continuously for years.
It also aims to double its reactor's power density every month as development progresses. This remains a stated engineering ambition, rather than evidence that such a rate of growth can be sustained in practice.
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