Scientists have achieved a groundbreaking milestone in the quest to construct the world’s first practical nuclear clock. In a study published in the journal Nature, a research team has demonstrated a novel method for observing the minuscule “ticking” of the thorium-229 nucleus. This approach completely bypasses the need for specialized transparent crystals, representing a major leap forward that could change precision timekeeping. This technology has the potential to transform global communications, deep-space exploration, navigation systems, and the prediction of earthquakes and volcanic eruptions.
Overcoming Technical Hurdles
This advancement builds upon a landmark success from last year, when researchers successfully used a laser to excite the nucleus of thorium-229 while it was housed inside a transparent crystal. That milestone was the culmination of 15 years of dedicated scientific effort. However, that achievement came with substantial practical limitations.
Dr. Harry Morgan, a co-author of the research and a Lecturer in Computational and Theoretical Chemistry at The University of Manchester, explained the challenges of the older technique. The transparent crystals required to hold the thorium-229 were technically demanding to produce and highly expensive. These factors placed severe limits on the ability to translate the laboratory success into a practical, real-world application. With the introduction of this streamlined approach, Dr. Morgan noted that there is little doubt left regarding the feasibility of a functional device.
A Radical Simplification
To bypass the costly crystal method, the research team achieved the exact same results by utilizing a microscopic thin film of thorium oxide. By electroplating a minute amount of thorium onto a standard stainless-steel disc — a process described as being similar to gold-plating jewelry — the scientists executed a radical simplification of their previous experimental setup. This new procedure uses only a tiny fraction of the material, making the entire method simple and inexpensive.
This breakthrough demonstrates that thorium-229 can be studied within far more common and opaque materials than scientists had previously assumed. By removing the reliance on specialized transparent crystals, the researchers have eliminated one of the most significant obstacles to building a practical nuclear clock.
The Mechanics of the Technique
The experimental process relies on the thorium nuclei absorbing energy emitted by a laser. After absorbing this energy for a few microseconds, the nuclei transfer it to nearby electrons, which can then be measured directly as an electric current. This method is known as conversion electron Mössbauer spectroscopy. While this spectroscopy technique has been utilized for years, it typically demands high-energy gamma rays inside specialized facilities. This study marks the first time the technique has been demonstrated using a standard laser within an ordinary laboratory.
Eric Hudson, a physicist at UCLA who led the research, noted that the team previously assumed the thorium needed to be embedded within a transparent material so that light could pass through. The team realized this assumption was incorrect. They discovered they can force enough light into an opaque material to excite the nuclei located near the surface. Instead of emitting photons — as happens within transparent crystals — the excited nuclei emit electrons. These electrons are detected by monitoring an electrical current, a process Hudson described as one of the easiest tasks to perform in a laboratory.
Beyond Timekeeping
While traditional atomic clocks rely on electrons to keep time, nuclear clocks utilize oscillations that occur deep within the nucleus itself. This fundamental difference makes the nuclear approach far less sensitive to external environmental disturbances, granting these devices the potential to be orders of magnitude more accurate.
Because of the principles outlined in Einstein’s theory of general relativity, these highly precise instruments should be sensitive to small fluctuations in the Earth’s gravity caused by the movement of rock and magma deep underground. By deploying these highly sensitive devices across active earthquake zones in regions like Japan, Pakistan, or Indonesia, scientists could monitor subterranean tectonic shifts in real time.
Dr. Morgan emphasized that this technology possesses the potential to revolutionize how humanity prepares for natural disasters. The technique also provides fresh insights into the decay and behavior of thorium-229, which could inform future energy research and the development of new nuclear materials. The research, funded by the National Science Foundation, involved physicists from UCLA, The University of Manchester, the University of Nevada Reno, Los Alamos National Laboratory, Ziegler Analytics, Johannes Gutenberg-Universität at Mainz, and Ludwig-Maximilians-Universität München.
