A recent study published in Nature details a significant advancement in the creation of practical nuclear clocks. Researchers have devised a new technique to observe the thorium-229 nucleus's "ticking" without requiring specialized transparent crystals. This breakthrough could lead to highly precise timekeeping devices with applications in navigation, communication, disaster prediction, and space exploration.
(a) Cut-away rendering of the 229ThO2 target mount. Arrows denote front aperture, window, target, and pyroelectric detector. (b) Rendering of the spectroscopy chamber. (Magenta arrow) Direction of VUV laser propagation. (Yellow arrows) IC electron trajectories from target to detection MCP. (Blue arrows) Background photoelectrons generated from VUV scatter diverted to secondary electrode. (Green arrow) Direction of static B-field used to guide IC electrons. (c) α-spectrum of the 229ThO2 target. (Inset) Photograph of 229ThO2 target used in this study. The peak labeled to 4845 keV corresponds to the dominant α-decay mode of 229Th. The other large peaks correspond to the α-decays of daughter nuclei. The 229Th peak had a FWHM of ∼22 keV, consistent with energy loss through a ∼10 nm sample, as estimated with SRIM [38]. Image Credit: University of Manchester
This development builds upon a previous achievement where the team successfully used a laser to excite thorium-229 nuclei within a transparent crystal, a goal they had pursued for fifteen years.
The new method allows for similar results using a much smaller amount of material and a simpler, more cost-effective process, paving the way for real-world nuclear clock technology.
Previously, the transparent crystals needed to hold thorium-229 were technically demanding and costly to produce, which placed real limits on any practical application. This new approach is a major step forward for the future of nuclear clocks and leaves little doubt that such a device is feasible and potentially much closer than anyone expected.
Dr. Harry Morgan, Study Co-Author and Lecturer, Computational and Theoretical Chemistry, The University of Manchester
The new method involves exciting the thorium nucleus within a microscopic thin film of thorium oxide. This film is created by electroplating a small amount of thorium onto a stainless-steel disc, a process comparable to gold-plating jewelry and a considerable simplification of their earlier technique.
In this process, thorium nuclei absorb energy from a laser. After a few microseconds, they transfer this energy to nearby electrons. This energy transfer can then be measured as an electric current. This technique, known as conversion electron Mössbauer spectroscopy, has been used previously but typically requires high-energy gamma rays and specialized facilities. This marks the first time it has been demonstrated using a laser in a standard laboratory setting.
The study demonstrates that thorium-229 can be studied within more common materials than previously believed. This overcomes a major obstacle in the development of practical nuclear clocks.
The technique also provides new insights into the behavior and decay of thorium-229. This knowledge could potentially inform the development of new nuclear materials and contribute to future energy research.
We had always assumed that in order to excite and then observe the nuclear transition the thorium needed to be embedded in a material that was transparent to the light used to excite the nucleus. In this work, we realized that is simply not true.
Eric Hudson, Physicist and Study Lead, University of California, Los Angeles
“We can still force enough light into these opaque materials to excite nuclei near the surface, and then, instead of emitting photons like they do in transparent materials like the crystals, they emit electrons which can be detected simply by monitoring an electrical current – which is just about the easiest thing you can do in the lab,” said Eric Hudson.
Similar to atomic clocks, nuclear clocks operate by utilizing the natural "ticking" of single atoms. However, atomic clocks measure electron processes, while nuclear clocks measure oscillations within the nucleus itself. This fundamental difference makes nuclear clocks less susceptible to external disturbances, offering the potential for significantly greater accuracy.
Nuclear clocks could also have applications in predicting earthquakes and volcanic eruptions. According to Einstein's theory of general relativity, nuclear clocks are sensitive to minute changes in Earth's gravity. These changes can be caused by the movement of magma and rock deep underground. By deploying nuclear clocks in seismically active regions, like Japan, Indonesia, or Pakistan, scientists could monitor subterranean activity in real-time, potentially enabling predictions of tectonic events.
Dr. Morgan added, “In the long term, this technology could revolutionize our ability to prepare for natural disasters. It’s incredibly exciting to think that thorium clocks can do things we previously thought were impossible, as well as improving everything we currently use atomic clocks for.”
The study received funding from the National Science Foundation. Participating institutions included physicists from the University of Nevada Reno, Los Alamos National Laboratory, Ziegler Analytics, Johannes Gutenberg-Universität at Mainz, and Ludwig-Maximilians-Universität München.
Journal Reference:
Elwell, R., et al. (2025) Laser-based conversion electron Mössbauer spectroscopy of 229ThO2. Nature. DOI:10.1038/s41586-025-09776-4. https://www.nature.com/articles/s41586-025-09776-4