An old jeweler’s trick could change nuclear timekeeping
A team of physicists has discovered a surprisingly simple way to build nuclear clocks using tiny amounts of rare thorium. By electroplating thorium onto steel, they achieved the same results as years of work with delicate crystals — but far more efficiently. These clocks could be vastly more precise than current atomic clocks and work where GPS fails, from deep space to underwater submarines. The advance could transform navigation, communications, and fundamental physics research.
Last year, researchers led by UCLA achieved a milestone that physicists had pursued for half a century. They succeeded in making radioactive thorium nuclei absorb and release photons in a controlled way, similar to how electrons behave inside atoms. The idea was first proposed by the team in 2008, and its realization is expected to open the door to a new generation of extremely precise clocks. These advances could dramatically improve navigation systems and may even help scientists test whether some of nature's fundamental constants change over time.
Despite the breakthrough, a serious limitation remained. The specific isotope required for nuclear clocks, thorium-229, is found only in weapons-grade uranium. As a result, scientists estimate that only about 40 grams of this material exist worldwide for clock research, making efficiency a critical challenge.
A simpler approach uses far less thorium
An international collaboration led by UCLA physicist Eric Hudson has now found a way around this bottleneck. The team discovered how to reproduce their earlier results while using only a tiny fraction of the thorium previously required. Their new method, reported in Nature, is straightforward and inexpensive, raising the possibility that nuclear clocks could one day become small and affordable enough for widespread use.
If that happens, these clocks could move beyond laboratories and replace timing systems in power grids, cell phone towers, and GPS satellites. They may even shrink enough to fit into phones or wristwatches. The technology could also enable navigation in places where GPS signals cannot reach, including deep space and underwater environments such as submarines.
Fifteen years of work replaced by a simple technique
Hudson's team spent 15 years developing the specialized thorium-doped fluoride crystals that enabled their original success. In those experiments, thorium-229 atoms were bonded with fluorine in a carefully engineered structure. The resulting crystals stabilized the thorium while remaining transparent to the laser light needed to excite the atomic nucleus. However, the process proved extremely difficult, and producing the crystals required relatively large amounts of thorium.
"We did all the work of making the crystals because we thought the crystal had to be transparent for the laser light to reach the thorium nuclei. The crystals are really challenging to fabricate. It takes forever and the smallest amount of thorium we can use is 1 milligram, which is a lot when there's only 40 or so grams available," said first author and UCLA postdoctoral researcher Ricky Elwell, who received the 2025 Deborah Jin Award for Outstanding Doctoral Thesis Research in Atomic, Molecular, or Optical Physics for last year's breakthrough.
Borrowing a method from jewelry making
In the new study, the researchers took a very different approach. They deposited an extremely thin layer of thorium onto stainless steel using electroplating, a technique commonly used in jewelry. Electroplating, developed in the early 1800s, relies on an electric current to move metal atoms through a conductive solution and coat one surface with another metal. For example, gold or silver is often electroplated onto less valuable metals.