  Examples are given which prove the ICARUS detector quality through relevant
physics measurements. We study the muon decay energy spectrum from a sample of
stopping muon events acquired during the test run of the ICARUS T600 detector.
This detector allows the spatial reconstruction of the events with fine
granularity, hence, the precise measurement of the range and dE/dx of the muon
with high sampling rate. This information is used to compute the calibration
factors needed for the full calorimetric reconstruction of the events. The
Michel rho parameter is then measured by comparison of the experimental and
Monte Carlo simulated muon decay spectra, obtaining rho = 0.72 +/- 0.06(stat.)
+/- 0.08(syst.). The energy resolution for electrons below ~50 MeV is finally
extracted from the simulated sample, obtaining (Emeas-Emc)/Emc =
11%/sqrt(E[MeV]) + 2%.
