Fusion Startup Claims It Turned Mercury Into Stable Gold

A San Francisco fusion startup says it has turned mercury into real, stable gold using neutrons from a fusion reaction, at a rate it claims is ten times the record CERN set in 2025. Marathon Fusion made the announcement on X on Wednesday, 21 October 2026, and the main post had been viewed nearly 2.9 million times by Thursday afternoon. The physics behind the idea is well understood. What the company has not yet shown publicly is how much gold it made, how pure it is, or any independent confirmation of the result.

Crystals of native gold, for illustration. Photo: Alchemist-hp via Wikimedia Commons, CC BY-SA 3.0 DE.

Key points

• Marathon Fusion says that "last month" it turned mercury into stable gold using fusion neutrons, at 10 times the record set by CERN in 2025.
• The method hits mercury-198 with fast neutrons from a deuterium-tritium fusion reaction. This produces radioactive mercury-197, which decays into gold-197, the only stable form of gold.
• For comparison, CERN's ALICE experiment estimated the Large Hadron Collider made about 29 picograms of short-lived gold over four years (2015-2018).
• Marathon's 2025 paper, based on simulations, projected about 2 tonnes of gold per year for each gigawatt of thermal fusion power. That is a projection, not demonstrated output.
• The company also says it has made medical isotopes (radioactive copper from zinc) and is building a fusion reactor in San Francisco.

What Marathon Fusion actually claimed

In a thread posted on 21 October, Marathon Fusion wrote: "Last month, we demonstrated high-rate alchemy: turning mercury into real, stable gold, beating CERN's record by a factor of 10." In the same post, it said it had enriched isotopes "in the world's most powerful plasma centrifuge, beating the Soviet record that stood for 40 years," and that it is now "building a fusion reactor in San Francisco to achieve record power density."

A later post in the thread linked the result to the company's earlier work: "In 2025, we published a bold proposal to use fusion reactors for gold production. And now we've done it." The company added that it has "reduced alchemy to a series of difficult but tractable engineering problems."

The thread also said Marathon has "already started producing our first medical isotopes," by turning zinc into radioactive copper isotopes used in cancer diagnostics and therapy. The company described itself as "a team of 28 and growing quickly." According to Business Today, the posts included energy-spectrum plots with peaks labelled as mercury-197 and gold-197, and as copper-64 and copper-67 in the zinc experiment.

As of Thursday, the claims rest on the company's own posts and charts. Business Today pointed out that the spectra can identify isotopes, but they do not show the total amount of gold produced, its purity, or the efficiency of the process. Marathon has not said which measure its "10x CERN" comparison uses.

How you turn mercury into gold

This is nuclear physics, not chemistry. Gold has 79 protons and mercury has 80. In Marathon's scheme, a deuterium-tritium fusion reaction releases a neutron carrying about 14 MeV of energy. When that neutron hits a mercury-198 nucleus, it can knock out two neutrons, a so-called (n,2n) reaction. That leaves mercury-197, which is unstable. Mercury-197 then captures one of its own electrons, turning a proton into a neutron, and becomes gold-197. Its half-life is roughly 65 hours.

Mercury-198 makes up about 10% of natural mercury. Marathon's 2025 paper, by Adam Rutkowski, Jake Harter and Jason Parisi, argued that a layer of mercury in a fusion reactor's "blanket" could make gold and also multiply neutrons, which helps the plant breed its own tritium fuel. The company's website says gold could take a gigawatt-scale plant's yearly revenue from about $223 million with electricity alone to about $482 million.

CERN's 2025 result came from a completely different process. Lead nuclei passing close to each other in the LHC can lose three protons and become gold. ALICE reported a peak rate of about 89,000 gold nuclei per second, but those nuclei broke apart almost immediately. That is why Marathon's claim of stable gold is the part people are paying attention to.

Reasons to be cautious

Experts were skeptical even before this week's announcement. Writing in The Conversation in July 2025, Adrian Bevan, a physicist at Queen Mary University of London, noted that Marathon's estimates came from a computer "digital twin." He said those assumptions "will remain untested" until commercial fusion reactors exist. He also warned that any gold made this way would at first be radioactive and would need to be managed as radioactive waste for some time.

Scale is the other problem. Marathon's own thread says that meeting demand would mean hitting a target "just 1 cm across, with a trillion neutrons, every second, continuously, for years on end." The company says it plans to double its power density "every single month." Business Today described that as an ambitious development target, not proof that the pace can be kept up.

Why it matters

Gold is the headline, but the bigger stakes are fusion's business model. Electricity is cheap, and fusion plants are expensive to build. If valuable by-products such as gold, tritium fuel or medical isotopes can be made at the same time, early plants could become easier to pay for. In the short term, medical isotopes are probably the more realistic market: Marathon's 2025 paper put the medical isotope market at around $5 billion a year. A peer-reviewed, independently checked measurement of how much gold was made, and how pure it is, would be the next real milestone. Until then, this is a striking claim from a small company, not proof that gold can now be made in a factory.

Related coverage: how a Russian satellite circled a US radar satellite · China's 13-foot hydraulic humanoid robot Neo1

Sources

• Marathon Fusion on X, announcement thread (21 October 2026)
• Business Today: Mercury to gold, Marathon Fusion claims 10x CERN record (22 October 2026)
• Rutkowski, Harter and Parisi: Scalable Chrysopoeia via (n,2n) Reactions Driven by Deuterium-Tritium Fusion Neutrons (Marathon Fusion, 2025)
• Marathon Fusion: Alchemy (company website)
• CERN: ALICE detects the conversion of lead into gold at the LHC (8 May 2025)
• The Conversation: Can we take this claim seriously? (Adrian Bevan, July 2025)
• Wikipedia: Isotopes of mercury (half-life and abundance data)