The layers of the Earth: the thin upper crust, the viscous upper and lower mantle, the liquid core and the solid inner core. |
Scientists
will soon be exploring matter at temperatures and pressures so extreme
that the conditions can only be produced for microseconds using powerful
pulsed lasers. Matter in such states is present in the Earth’s liquid
iron core, 2,500 km beneath the surface, and also in elusive “warm dense
matter” inside large planets like Jupiter. A new X-ray beamline ID24 at
the European Synchrotron Radiation Facility (ESRF) in Grenoble, France,
allows a new level of exploration of the last white spot on our globe:
the centre of the Earth.
We
know surprisingly little about the interior of the Earth. The pressure
at the center can be calculated accurately from the propagation of
earthquake waves; it is about three and a half million times atmospheric
pressure. The temperature at the center of the Earth, however, is
unknown, but is thought to be roughly as hot as the surface of the sun.
ID24,
which was inaugurated today, opens new fields of science, being able to
observe many rapid processes, like in a time-lapse film sequence,
whether laser-heating of iron to 10,000 degrees, charge reactions in new
batteries or catalysts cleaning pollutants. It is the first of eight
new beamlines to be built within the ESRF Upgrade Programme, a 180
million Euro investment over eight years, to maintain the world-leading
role of the ESRF. ID24 extends the existing capabilities at the ESRF in
X-ray absorption spectroscopy to sample volumes twenty times smaller and
time resolutions one thousand times better than in the past.
“Scientists
can use several other synchrotrons notably in Japan and the U.S for
fast X-ray absorption spectroscopy, but it is the microsecond time
resolution for single shot acquisition coupled to the micrometer-sized
spot that makes ID24 unique worldwide,” says Sakura Pascarelli,
scientist in charge of ID24. “The rebuilt ID24 sets the ESRF apart, and
even before the first users have arrived, I am being asked to share our
technology.”
The
Earth’s interior is literally inaccessible and today it is easier to
reach Mars than to visit even the base of the Earth’s thin crust.
Scientists can however reproduce the extreme pressure and temperature of
a planet’s interior in the laboratory, using diamond anvil cells to
squeeze a material and once under pressure, heat it with short, intense
laser pulses. However, these samples are not bigger than the size of a
speck of dust and remain stable under high temperatures only for very
short time, measured in microseconds.
Thanks
to new technologies employed at ID24, scientists can now study what
happens at extreme conditions, for example when materials undergo a fast
chemical reaction or at what temperature a mineral will melt in the
interior of a planet. Germanium micro strip detectors enable
measurements to be made sequentially and very rapidly (a million per
second) in order not to miss any detail. A stable, microscopic X-ray
beam means that measurements can also be made in two dimensions by
scanning across a sample to obtain a map instead of only at a single
point. A powerful infrared spectrometer complements the X-ray detectors
for the study of chemical reactions under industrial processing
conditions.
A catalytic cell with a sample heated under in situ conditions for analysis with a beam of X-rays. Image credit: ESRF/B. Gorges. |
Today,
geologists want to know whether a chemical reaction exists between the
Earth’s mostly liquid core and the rocky mantle surrounding it. They
would like to know the melting temperature of materials other than iron
that might be present in the Earth’s core in order to make better models
for how the core—which produces the Earth’s magnetic field—works and to
understand why the magnetic field changes over time and why
periodically in Earth’s history it has disappeared and reversed.
We
know even less about warm dense matter believed to exist in the core of
larger planets, for example Jupiter, which should be even hotter and
denser. It can be produced in the laboratory using extremely powerful
laser shock pulses compressing and heating a sample. The dream of
revealing the secrets of the electronic and local structure in this
state of matter with X-rays is now becoming reality, as ID24 allows
sample volumes 10000 times smaller than those at the high power laser
facilities to be studied, making these experiments possible at the
synchrotron using table top lasers.
The
ID24 beamline works like an active probe rather than a passive
detector, firing an intense beam of X-rays at a sample. The technique
used is called X-ray absorption spectroscopy and it involves the element
specific absorption of X-rays by the atoms in a material. From this
data not only the abundance of an element can be deducted but also its
chemical states and which other atoms, or elements, are in their
immediate neighbourhood, and even how far apart they are. In short, a
complete picture is obtained of the sample at the atomic scale.
ID24
has just successfully completed first tests with X-ray beams. Testing
will continue over the coming weeks, and the beamline will be open for
users from around the world as of May 2012. The date for the
inauguration on 10 November 2011 was chosen to coincide with the autumn
meeting of the ESRF’s Science Advisory Committee of external experts who
played a key role in selecting the science case for ID24 and the other
Upgrade Beamlines.
“ID24
opens unchartered territories of scientific exploration, as will the
seven other beamlines of the ESRF Upgrade Programme. The economic crisis
has hit our budgets hard, and it is not obvious to deliver new
opportunities for research and industrial innovation under these
circumstances”, says Harald Reichert, ESRF Director of Research. “I wish
to congratulate the project team for extraordinary achievements, and I
look forward to seeing some extraordinary new science.”
