Aging of proportional counters with gas mixtures containing impurities of aromatic hydrocarbons

The aging characteristics of some aromatic hydrocarbons and some other solvents with a ring like molecule structure are systematically studied. The concentrations ranging from a few ppm to several hundred ppm were investigated. Gas mixtures with and without hydrocarbons were tested as well, to find out whether the hydrocarbons contribute to the plasma polymerisation process. An array of twelve single-wire proportional counters, all receiving roughly the same irradiation dose from an X-ray device, was used for the accelerated aging tests. The aging rates were measured as a function of the concentration of the compounds under study. The results indicated that rate of aging is proportional to the concentration of aromatic hydrocarbons studied, and that the organic quenching component is taking part to the process by enhancing the aging rate. Outgassing of some construction materials was investigated as well. A thermal desorption tube was used for sampling the organic compounds released from the materials and a GC/MS analyser was used for the analysis. The method was utilised also for analysing the compounds created in the proportional counter due to the addition of the aromatic hydrocarbons.