Reading aloud To shoot a picture a little more complex than with a camera is already the procedure that Manfred Lindner from the Technical University of Munich and his colleagues came up with. To get information about the interior of the earth, the physicists want to capture neutrinos that have previously crossed the Earth. Instead of simply firing a flash like a photo, they have to wait for the next supernova to explode. The researchers present their procedure in the e-Print archive arXiv.org (hep-ph / 0207238). Roughly speaking, the interior of the earth consists of three layers: The earth's mantle, which is covered with the thin crust of the earth, extends to a depth of 2, 900 kilometers. Underneath lies the liquid outer core of the earth and at a depth of 5, 100 kilometers, the solid inner core follows. The geologists know that from the evaluation of earthquake waves. Just as light waves are partially reflected and partially refracted when air passes through glass or water, so does the earthquake waves at the boundaries between the various layers in the Earth's interior.

From the earthquake waves collected at the earth's surface, geologists can draw conclusions about the position of the boundaries between the layers and the density of the layers. However, information about the two core layers is the most difficult to obtain. In addition, the seismic waves primarily provide reliable values ​​over the density differences between two layers, but not over the absolute density values.

According to a theoretical calculation by Lindner and his colleagues, this is exactly the opposite with the method they suggest: from the measurement of neutrinos that have penetrated the earth, one can calculate well the average absolute density of the penetrated layers, but not local density fluctuations. In addition, the proposal of the Munich physicists allows a measurement of the Erdkerns with appropriate arrangement of the neutrino detectors.

With this inference, the Munich researchers are taking advantage of the recently confirmed theory of neutrino oscillations: According to this, the three neutrino varieties electron, mu and tau neutrino are constantly being transformed into each other. The clou: The conversion rate is influenced by the density of the permeated medium, which makes it possible to determine the density of the earth layers. display

According to the calculation of Lindner's team, the neutrinos emitted by the sun are not suitable for this process, but only the higher-energy neutrinos, which emit a collapsing supernova with at least eight times the mass of the sun within the first ten seconds of their collapse. The neutrinos can be intercepted by the existing neutrino detectors such as the Japanese super-Kamiokande.

Axel Tilleman

© science.de

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