Quantitative aging study with intense irradiation tests for the CMS forward RPCs

A systematic study with a series of irradiation tests was performed for the forward resistive plate chambers (RPCs) of the Compact Muon Solenoid (CMS) in the Large Hadron Collider (LHC) experiment. Small double-gap RPCs were manufactured and tested by the gamma rays emitted from a 200mCi137Cs source at Korea University and by the fast neutrons provided by the MC50 proton cyclotron at the Korea Institute Radiological and Medical Science (KIRAMS). We found no significant symptom of aging in the performance of the prototype RPCs, as a consequence of the neutron irradiation, whose total equivalent dose was approximately 45 Gy. However, a fast degradation was observed in the RPCs when the gamma signal rates were higher than 3kHzcm−2. Furthermore, we observed from the chemical analysis for the RPC electrode that the long-term performance of the RPCs was stable in spite of absorbing the high-level fluorine when the signal rates were lower than 2kHzcm−2.