AGING STUDIES WITH ARGON METHANE BASED GAS-MIXTURES/

Ageing studies on a single wire proportional counter with Ar/CH4 (90: 10) (P10) and Ar/CH4/H-2 (89.5:10:0.5) (P10/H-2) mixtures irradiated w ith 6.4 keV X-ray photons from an X-ray generator, under well controll ed conditions, are reported. For both mixtures, results are presented for the variation of the gain as a function of the accumulated charge per centimetre of the wire. The intensities of the main emissions (CI line at 193.1 nm and of the CH (A-X, B-X, C-X) molecular bands centred , respectively, at 431, 389 and 314 nm) are also measured. No ageing e ffects were observed up to an accumulated charge of 350 mC/cm with the P10/H-2 mixture. The tests performed with P10 following the P10/H-2 r un, both for low and high irradiation rates, showed also negligible ag eing, in contradiction with previous results. This may indicate that t here is still some hydrogen adsorbed in the system that prevents the c hamber from ageing.