MACRO TRD upgrading and measurement of the underground muon energy spectrum: The MACRO Collaboration

A transition radiation detector (TRD) consisting of three identical modules each of 12 m2 area, has been developed and installed on the MACRO detector at the Gran Sasso National Laboratory (LNGS). The modular structure based on single proportional tubes and polyethylene foam radiators, allows to cover a large area. A gas gain monitoring system has been recently installed to check the detector stability. The TRD is able to measure, the muon energy spectrum up to 1 TeV and in a saturated way, to higher energies. The integral spectrum of muon from data collected in one year by the 1st module is presented.