Researchers at TU Wien report building the first self-stabilizing nuclear clock, according to ScienceDaily. Instead of relying on electron transitions in atoms, the device uses thorium nuclei as its timekeeping reference. Earlier nuclear-clock setups depended on a conventional atomic clock to stay stable; the new system maintains its own laser frequency through feedback and ran for more than 24 hours without intervention.
Thorium is central to the design because two of its nuclear energy states are separated by an unusually small gap, allowing a laser to drive the transition. The team, led by Thorsten Schumm, previously worked with Ekkehard Peik's group to show that laser light could excite thorium nuclei and later connected the setup to an optical atomic clock. The new advance adds the missing self-stabilizing mechanism: if the laser frequency drifts, thorium nuclei absorb less light, and the system automatically corrects the laser.
Because atomic nuclei are far smaller than atoms, they are less sensitive to environmental disturbances such as temperature fluctuations. The prototype reached a relative precision of about 10^-15, equivalent to roughly one second in 30 million years. The researchers say nuclear clocks could in principle achieve much higher precision than atomic clocks, though this remains an early demonstration.