Energy resolution of xenon proportional counters: Monte Carlo simulation and experimental results

The gas multiplication factor M and energy resolution R of xenon gas cylindrical proportional counters are investigated experimentally and calculated theoretically using a Monte Carlo technique to simulate the growth of single-electron-initiated avalanches. A good agreement is found between calculated and experimental data. The experimental and the calculated results are presented as a function of the reduced voltage K and the reduced anode radius Na, where N is the number density and a the anode radius. The Monte Carlo results for the intrinsic energy resolution R_int are discussed in terms of the parameter f which characterizes the statistical fluctuations of the avalanche gains. The present calculations have revealed that there is an intrinsic dependence of f on the critical value S_c of the reduced electric field at the onset of multiplication. This has enabled the parameterization of f and of the intrinsic energy resolution R_int in terms of the reduced voltage K only and has explained why, for a given range of operating values for M, energy resolution in a cylindrical proportional counter is improved for thinner anode wires and lower pressures