Nuclear Breakthrough Might Help Create the Most Accurate Clock Ever

A new study from Germany could help make nuclear clocks a reality — leap-frogging atomic ones.
Brad Bergan

A new kind of clock is in town, and it could stand poised to add an order of magnitude to the precision atomic clocks offer — and it measures time based on the nucleus of thorium-229, according to a recent study published in the journal Physical Review Letters.


Nuclear clocks leap-frog atomic ones

The most accurate clock in the world is based on the ticking of electrons inside an atomic shell — and the best atomic clocks have an accuracy of one part in 10^18, reports Science Alert. This is a level of precision that wouldn't have lost a single second since the universe began, billions of years ago.

Now a new kind of clock based on a thorium isotope's nuclear ticking is on the rise. But the idea — first suggested in 2003 — has proven difficult to make a reality.

"A plethora of applications and investigations have been proposed for the 229mTh state, ranging from a nuclear gamma laser, a highly accurate, and stable ion nuclear clock to a compact solid-state nuclear clock," wrote the researchers in their paper.

These new clocks should give probes designed to research fundamental physics unprecedented levels of precision — including the search for dark matter, the idea of varying fundamental (universal) constants, or even as a gravitational wave detector.

"They can be used in different applications, such as geodesy or satellite-based navigation," added the researchers in the study.

Atomic clocks require less energy than most nuclear ones

Atomic clocks use atoms from specific elements like ytterbium or strontium — which are irradiated with lasers. This process excites electrons in atomic shells, and makes them oscillate to and fro between different energy states.

The resulting oscillations are created when electrons shift (or transition) between energy levels — which is triggered via specific wavelengths of electromagnetic radiation, Science Alert reports.

Nuclear clocks would use the same principle, but instead of electrons, they'll rely on the oscillation of the nucleus itself.

However, atomic nuclei require high amounts of energy for transition — in the kilo- to megaelectronvolt range. To become excited enough to oscillate, these nuclei need energy on the scale of X-rays or gamma rays instead of simple lasers — which makes them less-than-practical for common timekeeping.

Sadly, we don't have lasers that powerful.

Thorium-229 requires much less energy

Thorium-229, on the other hand, is a rare exception. Among thousands of known atomic nuclei, the excited state of thorium-229 nuclei is the lowest-known by a wide margin — in the electronvolt range. This is so low it only needs ultraviolet irradiation to oscillate.

While several attempts to narrow down the exact ultraviolet wavelength of light needed to excite the nucleus and achieve a functional nuclear clock — none have surpassed the latest one from physicist Tomas Sikorsky of Heidelberg University in Germany, the country that never stops giving to the world of engineering marvels.

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