Manifestation of aging effects in gas proportional counters

Studies of the behavior of cylindrical proportional tubes, 25 and 32.1 mm in diameter, under sustained irradiation were carried out with Ar/iso-pentane 95:5 and Ar/CO2/N2/iso-pentane 70:10:10:10 gas mixtures. The influence of aging on the decrease of gas gain and on the so-called count rate effect was studied. Special attention was paid to the performance of aged counters operated at high gas gain and at high counting rate. A very strong impact of aging on the count rate effect was observed. The decrease of gas gain was found to be a linear function of the collected charge.