Results about HF production and bakelite analysis for the CMS Resistive Plate Chambers

The formation of reactive compounds in the gas mixture during Resistive Plate Chambers (RPCs) operation at the CERN Gamma Irradiation Facility (GIF) is studied. Results from two different types of chambers are discussed: 50×50cm2 RPC prototypes and two final CMS-RB1 chambers. The RB1 detectors were also connected to a closed loop gas system. Gas composition and possible additional impurities have been monitored in different gamma irradiation conditions both in open and closed loop modes using a gas chromatograph. Dedicated measurements for fluoride concentration in the exhausted gas line were performed at different irradiations and operation conditions using a specific electrode and a High-Performance Liquid Chromatograph. The efficiency of the purifiers system present in the closed loop in removing the F-F- and others impurities has also been investigated. Finally, the chemical composition of the RPC electrode surface has been analyzed using an electron microscope equipped with an EDS/X-ray.