Application of muon tomography to detect radioactive sources hidden in scrap metal containers

The accidental melting of radioactive sources hidden inside metal scrap containers can produce severe environmental harm. Modern melting facilities are equipped with portals measuring radiation levels. Nonetheless, sources can pass undiscovered when shielded inside shells of high density material, such as lead. From time to time indeed some radioactive sources pass undetected through the controls at foundries entrance. Once melted they caused enormous damages to the steel mills, contaminating all the production line. The muon tomography technique allows to discriminate high- Z materials measuring multiple scattering of cosmic ray muons inside matter. Therefore this technique can be used to analyze a truck container searching for high-density source shields. We report here the results about simulation studies of a muon tomography portal. Within the Mu-Steel European project we developed the prototype design, the three-dimensional images reconstruction software and the high density material identification algorithm. MonteCarlo simulation was validated with data from a large volume demonstrator (~11 m³) built using spare muon drift-time chambers of the CMS high energy physics experiment operating at the Large Hadron Collider at CERN.