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Products and solutions, 2010-06-21, 11:00 AM

ICARUS experiment launched: ThyssenKrupp VDM helps in the search for ghost particles from space, the mysterious neutrinos

Every second, tiny particles – invisible to the human eye – fall on the earth’s surface and penetrate our planet at a rate of around 60 billion per square centimeter. These so-called neutrinos are sometimes referred to as ghost particles because they pass through matter without colliding with other particles. “Of all known particles, neutrinos are the most mysterious,” say scientists. To solve the mystery, a test facility has been set up in Italy equipped with instrumentation featuring high-performance materials from ThyssenKrupp VDM. After years of preparation and testing, the scientists now report that work on the pioneering project has begun. The experiment is being carried out in the world’s largest underground laboratory for astroparticle physics, built beneath 1,400 meters of rock. Researchers hope it will lead to new findings on the past and future of the universe.

Neutrinos are produced by nuclear reactions such as those that take place on the sun and in supernova explosions. Since the mysterious particles pass through matter without interacting with it and without leaving a mark, they are virtually impossible to detect. This means that large and extremely sensitive instruments (detectors) are needed to record the tiny particles. One such instrument is the ICARUS particle detector, for which ThyssenKrupp VDM supplied some 70 metric tons of the high-performance material Pernifer 36 in the form of hot-rolled plate. The name of the ICARUS program stands for “Imaging cosmic and rare underground signals”. The centerpiece is an 80 meter long, 15 meter tall measuring unit operated by the Italian “Laboratori Nazionali del Gran Sasso” (LNGS). 600 to 800 scientists from 25 countries come here each year to carry out experiments. To ensure the investigations can be conducted without interference from background radiation, the 600 ton detector is located deep below the surface of the Gran Sasso, a mountain range in the Abruzzo region of Italy, around 120 kilometers south of Rome.

Since August 2006 the world renowned nuclear research institution CERN (Conseil Européen pour la Recherche Nucléaire) in Geneva has been directing a stream of man-made neutrinos to this underground laboratory. Particle accelerators generating energy levels similar to those produced by nuclear fusion release neutrinos which are then sent on a 730 kilometer journey to the ICARUS detector. Traveling through the earth’s interior, the ghost particles complete the trip in 2.5 milliseconds.

The detector is subject to extreme requirements. This is why a special high-performance material, the nickel alloy Pernifer 36 was used, as it displays exceptionally low thermal expansion, good processing characteristics and outstanding mechanical properties at extremely low temperatures. “The complete interior of the detector is made of Pernifer 36”, reports Francesco Arneodo of the LNGS. The detector is filled with liquid argon. When neutrinos enter this so-called bubble chamber, they react with the inert gas and cause flashes of light, which trigger several cameras. A three-dimensional image of the neutrinos is produced. “The thermal expansion coefficient of Pernifer 36 is of enormous importance for the shape of the detector, which is cooled to minus 186 degrees by the liquid argon,” explains Dr. Bernd de Boer, Head of Application Technology, ThyssenKrupp VDM: “Pernifer 36 does not become brittle at low temperatures and temperature fluctuations cause virtually zero expansion of the material.”

For the scientists, the research into neutrinos will also unlock secrets of the universe. Because the mysterious particles traverse space unimpeded for eons, they can provide information on past events in outer space or the so-called “black holes” and are therefore messengers of the cosmos. “The main results of the investigations are not yet available,” says Arneodo, adding: “But with studies into the behavior of liquid argon, ICARUS is already making a major contribution to elementary particle physics.” The nuclear physicists have now announced that the detectors were started up at the end of May, which means that work on the ICARUS experiment itself has begun.

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