For centuries, alchemists from Egypt to Enlightenment Europe dreamed of transmuting common substances into precious ones. They never managed to find the fabled “Philosopher’s Stone”, but early alchemists laid the basis for modern chemistry, with all the amazing science that came out of it. But now, an engineering company called Marathon Fusion says it has a real shot at gold transmutation — using the same kind of nuclear fusion reactions that power the Sun.

The company’s co-founders, both in their early 30s, have outlined a plan to use high-energy neutrons produced in fusion reactors to transmute mercury into gold. The idea may sound like science fiction or even pseudoscience. But it’s grounded in nuclear physics, and some scientists are paying attention — so maybe we should too.

“On paper it looks great and everyone so far that I talk to remains intrigued and excited,” Dr. Ahmed Diallo, a plasma physicist at the Department of Energy’s Princeton laboratory, told the Financial Times.

The paper, which has yet to undergo peer review, describes how one isotope of mercury (mercury-198) could be bombarded with neutrons inside a fusion reactor. Those reactions would produce a radioactive isotope, mercury-197, which decays over a few days into stable gold-197, the naturally occurring form of the precious metal.

The Gold Standard in Neutrons

Most fusion reactors under development, including the tokamak systems favored by Marathon Fusion, rely on fusing deuterium and tritium — two heavier forms of hydrogen — to produce helium and neutrons. These reactions unleash extraordinary amounts of energy, mostly in the form of high-speed neutrons.

Traditionally, those neutrons are captured in what’s called a “breeding blanket,” designed to produce more tritium from lithium so the reactor can sustain future fuel cycles.

Marathon’s innovation is to sneak a little mercury into that blanket. Specifically, mercury-198, which is a stable isotope that makes up about 10% of natural mercury. When hit with a neutron, it becomes mercury-197, which in turn decays into gold.

“The key insight here is that you can use this set of fast neutron reactions to make really large quantities of gold while satisfying the fuel cycle requirements of the system,” said Adam Rutkowski, Marathon’s chief technology officer and a former engineer at SpaceX.

Rutkowski and co-founder Kyle Schiller estimate that one gigawatt of fusion electricity — roughly the output of a large nuclear or coal plant — could yield up to 5,000 kilograms of gold annually. At today’s market prices, that’s over $550 million worth of gold per year per GW of fusion energy.

The real kicker? That revenue would come without sacrificing energy output or tritium production, effectively doubling the financial return of a fusion power plant since the gold generated is thought to be worth about as much as the electricity.

Precious Metals, Practical Limits

The proposal is sure to turn heads, but how feasible is it? It’s really complicated, that’s for sure.

First, natural mercury is a cocktail of several isotopes. When exposed to neutrons, some of those other isotopes may form unstable varieties of gold — ones that are radioactive. Rutkowski acknowledged that the resulting gold may need to be stored for over a decade before it’s safe to touch or sell.

“There’s probably a storage period of 14 to 18 years before it could be labeled completely safe,” he said.

Marathon also believes the process could be adapted to create other precious metals. But gold, with its steady demand and limited supply, seems ideal. Global gold mining yields roughly 3,500 tons per year. Adding a few more from fusion reactors, the team argues, wouldn’t flood the market.

“Gold is in that sweet spot,” Dan Brunner, a scientific adviser to Marathon and former chief technology officer at Commonwealth Fusion Systems, a firm backed by Bill Gates, told the Financial Times. “From a purely scientific perspective, it looks like it all hangs together. I think the challenge comes into actually engineering it into a practical system.”

Indeed, making fusion work at all — let alone as a commercial power source — remains one of modern science’s greatest challenges.

Scientists have succeeded in fusing atoms since the 1930s. But no one has yet built a reactor that produces more energy than it consumes, in earnest. Dozens of companies and research institutes are trying. In the past year alone, fusion startups raised $2.6 billion, bringing global investment to nearly $10 billion across 53 firms, according to the Fusion Industry Association.

Marathon Fusion, a relative newcomer founded in 2023, has raised $5.9 million in private funding, along with $4 million in U.S. government grants. Its staff includes just a dozen full-time employees. Still, the startup managed to present its work to Bill Gates at the 2024 Breakthrough Energy Summit in London.

Alchemy, Reimagined

The idea of nuclear transmutation isn’t new. In fact, physicists at CERN reported earlier this year that they observed lead atoms transforming into gold in rare high-speed collisions inside the Large Hadron Collider.

But such events are fleeting, microscopic in output, and — crucially — wildly expensive. Using particle accelerators to make gold has always been a scientific experiment, not a business proposition.

Marathon’s approach, if proven viable, would flip that equation. It doesn’t rely on billion-dollar particle beams. Instead, it would ride along the same neutrons already needed for fusion power.

Malcolm Handley, founding investor of Marathon through his fund Strong Atomics, believes the possibility of gold revenue could turbocharge fusion development across the industry.

Fusion companies, he said, had “signed up for a lot of hard problems.” If gold can help solve some of them, that might be worth its weight in — well, gold.

“The money this will unlock will make all of those problems easier,” Handley said.

If fusion energy ever lives up to its promise — delivering limitless clean electricity from the atoms that fuel stars — it will already have transformed the world. But if it can mint gold on the side? That might be the final, gilded twist in the story of alchemy.