THE ENERGY RESOLUTION OF PROPORTIONAL-COUNTERS WITH THIN ANODE DIAMETERS DOWN TO 5 MU-M

An investigation of the energy resolution of a conventional cylindrica l proportional counter with thin anode diameters from 5 mum to 20 mum has been carried out for pure argon and argon + 10% methane at 1 atm. With argon + 10% methane the energy resolutions for 5 mum, 10 mum, and 20 mum anode wires were 13.5%, 13.7%, and 14.1% at 5.9 keV and a gas gain almost-equal-to250, respectively. An analysis of the first Townse nd ionization coefficient shows that the superior energy resolution fo r the thinner anode wire is due to the effect of the stronger reduced electric field at the beginning portion of the avalanche region. This has important implications for microstrip gas counter where the (firml y supported) anodes can be made arbitrarily small, far finer than thos e possible in conventional wire chambers.