Proposed Thorium Neutron-Based Clock Would be Accurate for Billions of Years


An ultra-high vacuum chamber houses an ion trap where single thorium atoms are suspended and laser-cooled to near absolute zero temperature. Credit: Alexander Radnaev

Scientists are proposing the building of a hyper-accurate nuclear clock that would lose only one-tenth of a second over 14 billion years, the current age of the universe. This design would be 100 times more accurate than atomic clocks available today and could be used in applications such as high-precision GPS satellites, and experiments that probe the fundamentals of physics and relativity.

Normal atomic clocks measure time using the oscillations of a single atom. Time is calculated to 17 decimal places and such precision is needed for GPS measurements and synchronization in particle accelerator experiments. The findings will be published in an upcoming issue of the journal Physical Review Letters.


Errant magnetism, electrical fields, and microscopic jostling make atomic clocks drift about four seconds over 14 billion years. The new clock would measure time on the oscillations of a neutron, which isn’t susceptible to vibrations or electromagnetic forces.

Researchers would excite a single thorium atom’s nucleus with an ultraviolet laser, and then use the oscillations of the neutrons as a way to measure time. The whole clock would have to be cooled down to just about absolute zero.

All the technical components are possible with today’s science, but physicists still need to know the exact frequency of the ultraviolet laser emissions so that they can excite the thorium nucleus the right way.

Reference: “Single-Ion Nuclear Clock for Metrology at the 19th Decimal Place” by C. J. Campbell, A. G. Radnaev, A. Kuzmich, V. A. Dzuba, V. V. Flambaum and A. Derevianko, 22 March 2012, Physical Review Letters.
DOI: 10.1103/PhysRevLett.108.120802

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