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An innovative X-ray method enables new high-pressure investigations of samples under deep mantle conditions. The technique, which was developed by a team led by Georg Spiekermann from DESY, the German Research Centre for Geosciences GFZ and the University of Potsdam, extends the range of instruments available to high-pressure researchers. Successful tests of the new method at DESY's X-ray light source PETRA III support the idea that heavy elements have to accumulate in magmas so that they could be stable at depths of Earth's lower mantle. The scientists present their work in the journal Physical Review X.
The so-called standard conditions of chemistry, i.e. a temperature of 25 degrees Celsius and a pressure of 1013 millibar, are actually rare in nature. Most of the matter in the universe exists under completely different conditions. In Earth's interior, for example, pressure and temperature rise rapidly to many times the standard conditions. "However, even with the most elaborate deep drilling, only the uppermost part of the Earth's crust is accessible," Spiekermann emphasises. Researchers therefore simulate the conditions of Earth's interior in the laboratory in order to investigate the behaviour of matter under these conditions.
Experiments - Structure - Samples - Materials - Changes
Such experiments often involve determining the inner structure of the samples, which in many materials changes with increasing pressure. This inner structure can be explored with X-rays that are energetic enough to penetrate the sample and short enough in wavelength to resolve the tiny details of atomic distances. For this purpose, usually two X-ray based methods exist in high-pressure research: absorption and diffraction of X-rays through the sample.
Based on X-ray emission, Spiekermann and his team have now developed a third method that can be used to determine both the bonding distances in compressed amorphous (disordered) matter and the so-called coordination number, which indicates how many direct neighbours an atom has. These parameters...
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