Muon radiography with the CMS Muon Barrel chambers

The drift tube chambers developed for the muon barrel system of the CMS experiment at CERN are large area detectors with 8 measurement points in one direction and 4 in the other; each point has a resolution of about 200 mum. We are using two of such chambers for muon radiography, i.e. the detection and imaging of material with high atomic number Z through the measurement of the multiple scattering of cosmic- ray muons crossing the material itself. The chambers are self- triggered, using the trigger electronics developed for the CMS experiment. Such technique might be applied for example in cargo container inspection searching for high-Z materials. Our apparatus is composed by two chambers with a 7 m² active area. In the gap between the chambers a container and the target material can be placed. Other two drift tube chambers, each with 4 measurement points, interleaved by a thick plane of Fe, give a rough determination of the cosmic muon momentum. We present results on the detection capability and performance of the system.