The energy resolution of proportional counters with thin anode diameters down to 5 /spl mu/m

An investigation of the energy resolution of a conventional cylindrical proportional counter with thin anode diameters from 5 /spl mu/m to 20 /spl mu/m has been carried out for pure argon and argon+10% methane at 1 atm. With argon+10% methane the energy resolutions for 5 /spl mu/m, 10 /spl mu/m, and 20 /spl mu/m anode wires were 13.5%, 13.7%, and 14.1% at 5.9 keV and a gas gain /spl ap/250, respectively. An analysis of the first Townsend ionization coefficient shows that the superior energy resolution for 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 a microstrip gas counter where the (firmly supported) anodes can be made arbitrarily small, far finer than those possible in conventional wire chambers.<>