Design of a large area tomograph to search for high-Z materials inside containers by cosmic muons

In recent years the need to have a better control of potentially dangerous materials across the borders has raised the opportunity to search for alternative detection techniques. In particular, to detect the presence of hidden high-Z materials inside containers, traditional techniques based on X-rays or neutron scattering are of limited use, and prototypes of detection systems based on cosmic muon scattering from high-Z materials are being tested worldwide to overcome these limitations. The use of this method is particularly suited to this aim, since it does not introduce additional radiation levels to the already existing natural dose. Since the technique is based on the scattering process of muons and not on their absorption, each event may in principle contribute to produce the tomographic image. A new Project has recently started by the Muon Portal Collaboration, which plans to build a large area muon detector, able to reconstruct muon tracks with good spatial and angular resolution. The design and operational parameters of the tomograph under construction are here described, together with preliminary simulation and test results of the individual detection modules. Due to the large acceptance of the detector for cosmic rays, coupled to the good angular reconstruction of the muon tracks, it is also planned to employ such detector in the future for cosmic ray studies, complementing its detection capabilities with a set of trigger detectors located some distance apart, in order to measure multiple muon events associated to extensive air showers.