A new technique for studying the Fano factor and the mean energy per ion pair in counting gases

A new method is presented for deriving the Fano factor, F, and the mean energy per ion pair, Wi, in counting gases. It is based on the technique of individual counting of single ionization electrons induced in low-pressure gas samples by soft x-ray photons. A correlation of the experimental data with a detailed simulation of the electron deposition and counting process permits the extraction of the Fano factor and the mean energy per ion pair values. We present data of F and Wi for C2H6 and Ar/C2H6 over the energy range of 100–1500 eV. The energy dependence of these parameters reflects the atomic level structure of the gases. We discuss in detail the accuracy of this technique and its advantages and limitations. Ways are proposed for improving the technique and for broadening the energy range.