COSMIC-RAY MUON TOMOGRAPHY AND ITS APPLICATION TO THE DETECTION OF HIGH-Z MATERIALS

Each minute, about 10000 muons rain down on every square meter of Earth. These charged elementary particles are produced by cosmic rays striking the upper atmosphere. Millions of highly penetrative muons pass through our bodies, cars and houses daily. Penetrating the objects, muons interact with atoms of different materials, mainly electromagnetically. They are more strongly deflected, or scattered, by high-Z materials, including nuclear materials, like uranium and plutonium, and gamma-ray shielding materials, like lead, tungsten or gold. This allowed us to develop a technique which uses multiple scattering of cosmic-ray muons to detect shielded packages of nuclear materials in a background of normal cargo. The advantages of this technique are that it is passive, does not deliver any radiation dose above background, selective to high-z dense materials, and is suitable for large amount of shielding. Physical basis of the technique, current status of our research and its possible perspectives will be discussed.