FRONTIER RESEARCH
Nuclear clock could help blind
people, autonomous cars
navigate
28 September 2016
by Joe Dodgshun
Using lasers to measure energy fluctuations of Thorium-229 nuclei could pave the way for hyper-accurate nuclear clocks. Image credit:
nuClock
Measuring energy fluctuations in the nucleus of a rare radioactive element could improve the
accuracy of GPS from metres to centimetres, while marbled volcanic magma is being used to
create eruption countdowns, thanks to groups of European researchers who are pushing the
boundaries of timekeeping.
From grains of sand in an hourglass to the position of the sun, people throughout history have used
different physical attributes in order to accurately tell the time. Today’s gold standard of timekeeping
are so-called microwave atomic clocks, which use microwave radiation to measure the oscillation of
electrons within a caesium atom.
The best of these are off by just one nanosecond in a month.
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Atomic clocks are used in the synchronisation of our increasingly complex power networks, stock
markets and mobile phone communications, but they don’t just set the world’s time. In the same way
that the first portable timepiece allowed sailors to navigate at sea, the relationship between distance
and time means atomic clocks underlie today’s satellite-based global positioning system (GPS).
However, while our standard GPS system allows triangulation of a device’s location to within a few
metres, Dr Simon Stellmer, a quantum optics researcher at the Vienna University of Technology in
Austria, says increasing satellite clock accuracy could cut this to a few centimetres, supporting not
only autonomous driving, but potentially also the mobility of millions of blind people around the world.
‘If you could have a cellphone or device that is able
to navigate blind people through cities with a few
centimetres’ precision, this would improve their
standard of life tremendously,’ explained Dr
Stellmer.
For this, an optical clock is needed, which uses
laser light rather than microwave radiation. In an
optical atomic clock the movement of electrons in
an atom sets the frequency of a laser which is used
as the equivalent of a pendulum in a grandfather
clock.
‘We want the same,
stable clock in the
US, in the EU and on
the moon.’
Dr Simon Stellmer, Vienna
University of Technology,
Austria
Optical atomic clocks are 100 times more accurate
than the microwave versions, but are susceptible to
environmental interference, limiting their use in
satellites. Thus, the EU-funded nuClock consortium
Dr Stellmer is coordinating is creating a different kind of optical clock.
‘Instead of electrons in an atom, it would be much nicer to use the nucleus, which is one hundred
thousand times smaller and less sensitive to environmental perturbations,’ Dr Stellmer said.
‘We want the same, stable clock in the US, in the EU and on the moon, one that is not dependent on
temperature, electric fields or any other freaky environmental effects.’
Thorium-229
nuClock team members from Ludwig-Maximilians University in Munich, Germany, last year confirmed
the existence of a long-suspected quirk in the rare radioactive element Thorium 229. This Cold War
research by-product is unique in that it has a relatively tiny energy fluctuation that occurs in the
nucleus, small enough to allow the creation of a nuclear clock.
A crystal doped with Thorium-229 could form the centrepiece of a future nuclear clock. Image courtesy of nuClock
Eight teams within nuClock, which is funded under the EU's Future and Emerging Technologies
programme, are now striving to find a way of measuring this oscillation, with at least two hoped to
succeed by 2017. Their goal is to have a working optical nuclear clock prototype ready by the project's
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end in 2019.
Dr Stellmer says this prototype might allow the measurement of the drift of fundamental constants in
physics, or have practical applications in geodesy — the study of the earth’s geometry, space
orientation and gravity, and how these change with time.
Because such clocks are so precise they give a more accurate measurement of how time runs
differently at varying heights due to gravity, which could be used to investigate underground processes
or cavities filled with substances of different density.
‘Prediction of earthquakes and volcanic activity would be something that one could try to measure, and
our clocks could also be used for underground exploration, measuring gravity and its gradient, to learn if
there are cavities, oil, gas, or whatever underground.’
Mixing magma
At the other end of the scale, the CHRONOS project, based in Perugia, Italy, is mixing magma to
develop countdowns for volcanic eruptions.
Dr Diego Perugini, who leads the European Research Council-granted project, says most of the earth’s
last 100 volcanic eruptions were caused by the phenomenon of magma mixing.
This happens when fresh, high-temperature magma bubbles up into a volcano chamber filled with stable
magma, releasing heat and gas as it mixes. This forms gas bubbles, lightens the magma viscosity and
builds pressure — and if this pressure is strong enough, it eventually forces the magma up through the
volcano channels and surges out in an eruption.
Dr Perugini says evidence of the extent of this magma mixing - and therefore the length of time
between its start and the volcano's eruption - is fossilised in volcanic rocks.
‘With a cappuccino, the longer you stir milk and coffee, the higher the homogeneity of the mixture and
the very same is true for magma. So the idea behind CHRONOS is to use the rock composition like a
broken clock at a crime scene; it tells you the time of the incident.’
To do this, the team have created the world’s first laboratory magma-mixing machine, which melts and
blends samples of volcanic rock components, employing chaotic mixing protocols to recreate a
volcano’s magma-mixing reaction. This reveals the maximum time from the start of mixing to eruption
— essentially a geochemical stopwatch.
Since every volcanic system is different in terms of the subterranean structure and the kind of magma
present, such a countdown would be different for every volcano.
The team last year created its first countdown, for the restless volcanic caldera of Campi Flegrei, close
to Napoli, Italy. It was found to have a maximum countdown of 20 minutes.
The next step is to investigate nearby Vesuvius, as well as the Soufrière Hills volcano, on the
Caribbean island of Montserrat, to create an inventory of these eruption timescales.
If the countdowns are long enough, CHRONOS will try to find links between magma mixing and
geophysical signals like earthquakes or ground deformation — something which Dr Perugini hopes
could be used as the basis for precise prediction of eruptions.
More info
nuClock
CHRONOS
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