discovered_01_2016 - Sleuthing with a Thermos

WWW.HZDR.DE discovered 01.16 RESEARCH The largest underground astrophysics lab is located in the Gran Sasso d’Italia Mountain in Italy. There, shielded by more than four thousand feet of rock, physicists from around the globe are searching for evidence of this mysterious Dark Matter. The shield of rock is necessary to ensure that the highly sensitive detectors only capture signals from unknown particles. But there is one troublemaker: natural radioactivity. The chemical element uranium is present in rock anywhere on Earth. Natural uranium is primarily uranium-238, which decays, just like any other isotopes of uranium following a certain temporal scheme. Every decay produces new atoms and particles – uranium-238 decays via what is called the uranium-radium-series, at the end of which is a stable lead isotope. What it is important to realize is that energetic alpha particles are emitted during decay, generating neutrons via nuclear reactions in the rock. The neutrons deep within the Gran Sasso Massif are partly a remnant of natural radioactivity but they also form in the shielding materials around detectors. So these particles can find their way to the detectors at the Italian National Institute for Nuclear Physics (INFN) and those of its international partners. These include the University of Mainz, which is majorly involved in the development and operation of a new xenon detector. This is a ten meter high tank filled with 3,500 kilograms of the liquid inert gas. Scientists from 21 institutions all over the world are involved in the XENON1T experiment in the Gran Sasso lab. // Dark Matter is everywhere, even though its existence has yet to be demonstrated. According to one popular theory, it might consist of what are called WIMPs. These Weakly Interacting Massive Particles are believed to pass through us unnoticed – millions of times per second. _TEXT . Christine Bohnet SLEUTHING WITH A THERMOS TARGET: The neutron source nELBE enables scientists to find out exactly how neutrons interact with matter. Photo: Oliver Killig

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