Underground muon energy spectra with the macro TRD

The MACRO detector was located in the Hall B of the Gran Sasso underground Laboratories under an average rock overburden of 3700 hg/cm(2). A TRD composed by three identical modules, covering an horizontal area of 36 m(2), Was added to the MACRO detector in order to measure the residual energy of muons entering MACRO. This kind of measurement provides a useful tool to study the primary cosmic ray energy spectra and composition, their interactions with the Earth's atmosphere and the propagation of muons inside the rock. The results of the measurement of the energy of single and double muons crossing MACRO will be presented. Our data show that double muons are more energetic than single ones in the rock depth range from 3000 to 6500 hg/cm(2). Single muon data confirm the reliability of the models adopted to describe the cosmic ray interactions with the atmosphere and the muon propagation inside the rock.