A transition radiation detector to measure the energy of cosmic ray muons in an underground laboratory

Abstract We have developed a transition radiation detector, of 1 m 2 active surface, to measure the residual energy of cosmic ray muonspenetrating in a Mont Blanc underground laboratory. Using polyethylene foils regularly spaced as radiators and argon filled proportional wire chambersto detect the transition radiation, we have been able to explore the muonenergy range from 0.1 to 0.5 TeV.