Study of the performance of the ATLAS monitored drift tube chambers under the influence of heavily ionizing α-particles

The MDT chambers of the ATLAS Muon Spectrometer will operate in a heavy LHC background environment mainly from photons and neutrons. The ionization produced by neutron recoils is much higher than the one from photons or muons and can be simulated by the use of alpha particles. A systematic study of the behavior of the ATLAS Monitored Drift Tubes (MDTs) under controlled irradiation has been performed. The presence of alpha particles results in the reduction of the gas gain due to space charge effects. The gas gain reduction has been studied in a single tube set up using a well controlled radium (²²⁶Ra) source in order to enrich the tube gas (Ar/CO₂) with the alpha emitter ²²⁰Rn and irradiate the tubes internally. The results are confronted with Garfield simulations.