ANODE WIRE AGING IN PROPORTIONAL-COUNTERS - THE PROBLEM OF ANALOG RESPONSE

The analog response of aged proportional counters is shown to be determined by the local charge density distribution on an insulating sense-wire surface. It therefore depends on a number of parameters such as spatial distribution of irradiation, counting rate, gas gain and surface conductivity of the insulating layer. Typical charge response time constants are derived from a dynamic model of the surface charge density. Experimental consequences such as charging-up effects, time dependence of amplitude in irradiation burst environments, fluctuations of detector resolution as a function of rate, and the influence of water admixtures on counting gases are described. The problem of deriving specific ageing parameters is quantified in a typical example.