Speaker
Description
In the context of particle physics, different families of gaseous detectors are operated with fluorinated-gases for different purposes. It is well known that under the effect of high electric field and radiation, fluorinated molecules may break and form, among other species, free fluorine ions. Such ions may react with water molecules present in the gas, leading to the formation of highly aggressive compounds that could affect the long term performance of the detector.
To quantify the production of fluoride several techniques are used by the CERN Gas Group. In particular, the use of Ion Selective Electrode was largely employed in both large LHC gas systems as well as small R&D setups.
In this study two different setups for measuring the F- concentration are shown. First, measurements were conducted on single gap, High Pressure Laminate RPC detectors of 2 mm installed at the CERN’s Gamma Irradiation Facility operated with different gas mixtures and under different gamma background radiation. The F- production of the standard gas mixture was compared with the one of the standard gas mixture with the addition of 30% CO2 at several gamma rates. Different concentrations of SF6 were also investigated to understand if and how the SF6 could affect the fluoride production. Finally, two gas mixtures containing R-1234ze, R-134a and He or CO2 were used to study the RPC fluoride production in presence of the R-1234ze, which is less stable in atmosphere with respect to the R-134a.
Second, a setup in collaboration with the CMS CSC group was built to evaluate the production of F- from straw tubes operated with a gas mixture of Ar/CO2/CF4 and Irradiated with a 90Sr source at different CF4 concentration and flow conditions. Preliminary tests and considerations on the setup are shown.
Finally, novel detection techniques to measure HydroFluoric acid and F2 molecules are presented.
