Monitored Drift Tubes aging under intensive gamma irradiation

The Monitored Drift Tubes (MDTs) are the key elements for precision tracking of the ATLAS muon spectrometer. In the era of LHC and forecasting an upgrade for SLHC it is crucial to test the detector robustness in the harsh background environment. Under LHC normal operation the expected total count rate is about 500Hz/cm2 for the innermost MDTs, while SLHC can reach fluxes 10 times higher. For a gas gain of 2×104, the overall accumulated charge can be as high as 6 C/cm/wire, which the MDTs must be able to withstand in 10 years of SLHC operation. In this paper, results of aging studies performed by irradiating two test detectors with photons from high intensity 60Co source at the ENEA Casaccia Calliope facility are summarized.