Pre-Installation tests of MWPCs for the LHCb Muon system

In order to minimize aging effects, the LHCb Muon chambers have to be operated at the lowest possible voltage, and in order to maximize the chamber efficiency, also at the lowest possible threshold. It is therefore crucial to have a good understanding of the noise characteristics of the system. An elegant method has been developed to determine the optimal threshold from noise measurements for each electronics channel. We present first the noise measurements made in laboratory with fully-equipped chambers for threshold optimization. The Gamma Irradiation Facility (GIF) at CERN was used to test the chamber performance under the intense gamma flux, similar to the one expected in the experiment. The results of tests of the various chamber types allow us to conclude that the requirements of the LHCb experiment are achieved.