Marathon Fusion claims to make gold from mercury, produce cancer-treatment isotopes

"Last month, we demonstrated high-rate alchemy: turning mercury into real, stable gold, beating CERN’s record by a factor of 10," Marathon Fusion said in the post. The company also said it had enriched isotopes using what it described as the world’s most powerful plasma centrifuge, surpassing a Soviet record that had stood for 40 years. "Now, we’re building a fusion reactor in San Francisco to achieve record power density," it said.

The startup did not disclose the quantity of gold produced in the experiment. Marathon Fusion’s proposed process uses nuclear transmutation, in which changes to an atom’s nucleus convert one element or isotope into another. Read Also: Left village at 13, built Rs 100-crore 'Shiv Sagar': How Narayan Poojari went from cleaning boy to restaurant owner In a research paper published in 2025, the company proposed using high-energy neutrons generated by deuterium-tritium fusion reactions to convert mercury-198 into mercury-197.

The radioactive mercury isotope subsequently decays into gold-197, the stable isotope of gold. The company had earlier estimated that a fusion power plant generating one gigawatt of thermal power could produce around two tonnes of gold annually through the process. Its latest X post said the company had demonstrated the conversion experimentally. However, it did not disclose the amount of gold produced or publish detailed experimental data alongside the announcement.

In 2025, CERN’s Large Hadron Collider produced gold nuclei through collisions involving lead nuclei. The European Organization for Nuclear Research reported the findings through its ALICE experiment, which measured the production of gold nuclei in the collider. The company said its work on fusion technology is also aimed at addressing shortages of radioactive isotopes used in medical applications, including targeted cancer therapies.

"Why? Because millions of lives depend on rare medical isotopes the world doesn’t have enough of," Marathon Fusion said in its X thread. It added that the adoption of targeted radiotherapies had increased rapidly, while existing reactors were unable to meet demand. Marathon Fusion has previously proposed using fusion-generated neutrons to produce copper-64 and copper-67 by irradiating zinc. Copper-64 is used in medical imaging and is being studied for therapeutic applications, while copper-67 is used in research and the development of targeted radiopharmaceutical treatments.

Marathon Fusion said its immediate focus was on developing a fusion reactor capable of achieving high power density, a measure of the power generated relative to the volume or area of a system. The company said it planned to double power density every month as it scaled up its technology. "To get there, we have to scale incredibly fast," it said, adding that it aimed to climb orders of magnitude above the performance of existing fusion reactors.

The startup said the technology being developed for smaller fusion reactors could also help establish the industrial base required for larger fusion power plants. Marathon Fusion's gold-production proposal was published in 2025, while its October 21 announcement reported a claimed experimental demonstration. The company has not disclosed the quantity of gold produced or provided a commercial production timeline in the post.