Drift properties of the ATLAS MDT chambers

A cosmic ray setup has been assembled, in order to verify that the BIS-MDT chamber fulfils the requirements of the ATLAS Muon Spectrometer. We use measurements obtained with this setup to study the drift time spectra of the MDT tubes and explain its features, by comparing them with the predictions of Garfield, Magboltz and Heed simulation programs. The drift time spectra have a peculiarity of a double peak. The second peak is a clear evidence of the Ramsauer dip of the electron cross-section.