Muons scanner to detect radioactive sources hidden in scrap metal containers (MU-STEEL) : final report

Most steel production is based on the recycling of scrap metal. Within this activity the accidental presence in the scraps of radioactive sources (orphan sources) is a relevant issue in the steel industries. The sources are usually contained in casks for safe transportation. If the shielding is sufficiently effective, the radiation detectors are useless and the identification is devolved to visual inspection. The most effective source identification method would be the classification of atomic number and density. This can be obtained by means of X- or gamma rays with energy high enough to achieve a sufficient penetration power, or by means of neutrons: steel penetration of 450 mm at least is needed. Both methods entail relevant safety issues, the need for qualified operators and high maintenance costs. The MU-STEEL project proposes an alternative technique based on the identification of the shielding casks using the muon tomography technique with the advantage of not using any artificial radiation. The naturally occurring muons are deflected by crossing a high-density material, the identification is based on the deflection measurement. Since this method does not identify radioactive material itself but the shield, it has to be used jointly with radiation portals. The project has produced a mechanical layout, a detailed design of a suitable muon detector and the first prototype. Moreover, a performing tomographic reconstruction software package has been developed and an extensive analysis of the potentiality of the technique has been carried out. Muon tomography appears suitable for reaching the requirements of the steel industries.