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Here’s what you’ll learn when you read this story:
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Scientists are close to creating a nuclear clock—an ultra-accurate clock that uses a low-energy transition in the nucleus of a thorium-229 atom to keep time.
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Electrical interference makes atomic clocks unsuited for dark matter detection, but nuclear clocks don’t have that problem, and could provide a resolution some 100,000 times better than what we currently have.
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There’s no guarantee that using a nuclear clock will finally find the theoretical perturbations caused by dark matter, but it will help scientists explore a new atomic realm as a part of that never-ending search.
Once considered an unusable byproduct of the U.S. nuclear program, thorium-229—an isotope of the silvery-white metal, thorium—could become central to humanity’s search for dark matter.
Up to this point, scientists have devised massive detectors, surveyed gravitational effects, and studied cosmic radiation in the hopes that it might point to evidence of this elusive substance. Now, researchers are considering whether a nuclear clock powered by the low-energy transitions of a thorium-229 nucleus may work as a new method in the particle hunt.
In a new study published in the journal Physical Review X, scientists from Germany, Israel, and Spain explored ways that the unique properties of a nuclear clock could detect the influence of dark matter. Today’s most accurate clocks (atomic clocks) rely on the oscillations of electrons between two quantum states to keep time. While highly precise, these clocks are susceptible to electrical interference. Proposed nuclear clocks, which use the nuclei of an atom, are far less impacted by these disturbances.
The resonance frequency—the steady swing of nuclei between “ground” and “high-energy” states—is typically pretty high, requiring strong radiation to excite the nucleus and produce the “tick-tock” of a nuclear clock. Thorium-229, however, is special because its resonance frequency is low enough to be excited by modern laser technology, theoretically making a nuclear clock possible.
“When it comes to dark matter a thorium-229-based nuclear clock would be the ultimate detector,” Gilad Perez, a co-author of the study from the Weizmann Institute of Science, said in a press statement. “Right now, electrical interference limits our ability to use atomic clocks in the search […]. We estimate [nuclear clocks] will enable us to detect forces 10 trillion times weaker than gravity, providing a resolution 100,000 times better than what we currently have in our search for dark matter.”
In the past year, labs around the world have made major breakthroughs in developing a thorium-229 nuclear clock, which culminated in a paper published in September of 2024 in the journal Nature. That paper reported an observation of a thorium-229 transition that was millions of times more accurate than previous attempts.
“In a universe made up only of visible matter, the physical conditions and the absorption spectrum of any material would remain constant,” Perez said in a press statement. “But because dark matter surrounds us, its wave-like nature can subtly change the mass of atomic nuclei and cause temporary shifts in their absorption spectrum […]. We still need even greater precision to develop a nuclear clock, but we’ve already identified an opportunity to study dark matter.”
There’s no guarantee that nuclear clocks will end our hunt for dark matter, but they do represent a new atomic frontier that has yet to be explored as part of that endless search.
Not so bad for an isotope once considered a mere “byproduct.”
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