UCLA physicist Eric Hudson and an international team of researchers have significantly advanced nuclear clock technology by demonstrating laser excitation of thorium-229 nuclei using a simplified method. Their work, detailed in Nature, replaces specialized fluoride crystals with thorium electroplated onto steel, achieving measurable electric current and paving the way for miniaturization. This innovation dramatically reduces the required amount of thorium—a globally scarce material estimated at only 40 grams—by approximately 90% while maintaining functionality. The advance promises to enable smaller, more efficient atomic clocks with impacts on navigation, power grids, and fundamental physics testing.
Laser Excitation of Thorium Nuclei Achieves Measurable Current
Researchers have achieved a measurable electric current by exciting thorium nuclei with a laser. This breakthrough simplifies the process previously reliant on specialized, difficult-to-grow fluoride crystals. The team electroplated a minute amount of thorium onto steel, utilizing a technique similar to that used in jewelry making. This new method requires 1,000 times less thorium than earlier experiments, addressing the limited global supply of approximately 40 grams of the necessary isotope, thorium-229.
The team discovered that the initial assumption of needing transparent materials for laser excitation was incorrect. They found they could stimulate the nuclei even within opaque materials, with the excited nuclei emitting electrons detectable as an electric current. This simplifies detection significantly – monitoring an electric current is described as “about the easiest thing you can do in the lab!” This advancement paves the way for smaller, more robust nuclear clocks.
This innovation has significant implications for various technologies, including navigation systems independent of GPS, improved power grid synchronization, and advancements in fundamental physics. Experts at Boeing and NASA’s Jet Propulsion Laboratory highlight the potential for compact, high-stability timekeeping and a solar-system-wide time scale for interplanetary travel. The research was funded by the National Science Foundation and involved collaborators from multiple international institutions.
Advancing Nuclear Clocks with Electroplated Thorium
Researchers have dramatically simplified the process of creating nuclear clocks using thorium, moving away from difficult-to-grow fluoride crystals. The team, led by UCLA physicist Eric Hudson, now uses electroplating – a technique dating back to the 1800s – to deposit a thin layer of thorium onto steel. This new method requires 1,000 times less thorium than previous techniques, crucial considering the limited global supply of only approximately 40 grams of the necessary thorium-229 isotope.
The breakthrough stems from realizing a key assumption was incorrect: transparency of the thorium’s surrounding material wasn’t necessary. Instead of emitting photons, the excited thorium nuclei in the opaque steel emit electrons, easily detected as an electrical current. This simpler detection method, combined with the reduced thorium requirement, promises significantly smaller and more robust nuclear clocks. The process initially took 15 years to develop the crystal method, but now leverages a much older industrial technique.
These next-generation clocks have broad implications, including improved navigation, power grid synchronization, and communication technology. Critically, they offer a potential solution for navigation in GPS-denied environments, like deep space or submarines, where current atomic clocks are insufficiently accurate or unusable. Experts at Boeing and NASA’s Jet Propulsion Laboratory highlight the potential for these clocks to revolutionize both aerospace applications and fundamental physics measurements.
Thorium-229 Availability and the Need for Efficiency
The limited availability of thorium-229—estimated at only 40 grams worldwide—presents a significant challenge for developing nuclear clocks. Researchers initially required 1 milligram of thorium embedded in specialized fluoride crystals to achieve results, a substantial amount given the scarcity of the isotope. However, a new method utilizing electroplated thorium onto steel dramatically reduces this requirement. This innovative approach uses 1,000 times less thorium, easing concerns about resource limitations and paving the way for wider application.
This new electroplating process simplifies construction and improves durability. Previous methods involved creating fragile fluoride crystals that were difficult to fabricate. The new technique, based on a centuries-old jewelry-making process, produces a robust piece of steel. Importantly, the team discovered that the thorium didn’t need to be embedded in a transparent material – light could still excite nuclei near the surface, and emitted electrons could be easily detected via electrical current.
The reduced thorium requirement and simpler process are crucial for potential widespread use of nuclear clocks. Applications extend beyond improving navigation, GPS, and power grids to enabling satellite-free navigation for scenarios like deep-sea submarines or GPS-denied environments. Furthermore, these clocks could revolutionize fundamental physics measurements and potentially contribute to establishing a time scale for future interplanetary travel and a permanent human presence on other planets.
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,”
Ricky Elwell
Impact of Nuclear Clocks on Navigation & Technology
Recent advancements are focused on creating smaller, more efficient nuclear clocks using thorium-229. A UCLA-led team successfully excited thorium nuclei to absorb and emit photons, a goal pursued for 50 years. This breakthrough simplifies clock construction by replacing difficult-to-grow fluoride crystals with thorium electroplated onto steel—a process similar to jewelry making. This new method uses 1,000 times less of the limited 40 grams of thorium-229 currently available worldwide, paving the way for potential integration into phones or wristwatches.
The key to this simplification was realizing that the thorium didn’t need to be embedded in a transparent material. Instead of emitted photons, the system detects electrons released when the thorium nuclei are excited by a laser, monitored simply by measuring an electrical current. This approach, utilizing a readily available industrial technique, creates a more robust and durable clock component—a small piece of steel—compared to the fragile crystals previously required.
These next-generation clocks promise improvements in navigation, power grids, and communications, and offer a solution to GPS-denied environments like deep space or underwater. Current atomic clocks used by submarines require surfacing to verify location after weeks, a limitation nuclear clocks could overcome. Experts at Boeing and NASA JPL highlight the potential for compact, high-stability timekeeping and revolutionary advancements in fundamental physics measurements, including tests of Einstein’s theory of relativity.
In my opinion, thorium nuclear clocks could also revolutionize fundamental physics measurements that can be performed with clocks, such as tests of Einstein’s theory of relativity.
Eric Burt
Years of Research Lead to Simplified Clock Design
Years of research have culminated in a simplified design for nuclear clocks, building on a 2008 proposal and a 2024 breakthrough. Initially, scientists spent 15 years creating specialized fluoride crystals to stabilize thorium-229 and allow laser excitation of its nucleus. However, this required significant amounts of a rare isotope—only about 40 grams exists globally. This new work demonstrates that these complex crystals are unnecessary, paving the way for more economical and accessible timekeeping technology.
The team discovered that thorium electroplated onto steel works just as effectively, requiring 1,000 times less of the scarce isotope. This process, similar to techniques used in jewelry making since the early 1800s, deposits a thin layer of thorium. Crucially, the researchers found that the thorium didn’t need to be embedded in a transparent material; detectable electrons emitted from the excited nuclei can be measured as an electrical current.
This simplified method promises smaller, more durable nuclear clocks with broad applications. Beyond improving navigation, power grids, and communication, these clocks could enable satellite-free navigation for submarines or deep space travel. Experts at Boeing and NASA JPL acknowledge the significance of this approach, anticipating that it could revolutionize both timekeeping technology and fundamental physics measurements.
