Electron degradation and yields of initial products: V. Degradation spectra, the ionization yield, and the Fano factor for argon under electron irradiation

The electron-degradation spectrum is fundamental for describing a variety of quantities bearing on electron slowing-down processes in matter. We calculate the electron-degradation spectrum in Ar gas by solving the Spencer-Fano equation, using a realistic set of cross sections. The influence of Auger electrons on the degradation spectrum is studied in detail. As an application, we study the statistical fluctuations in the ionization yield, which are expressed in terms of the Fano factor F(T) for an electron incident at fixed energy T. The energy dependence of F(T) is greatly influenced by L-shell ionization. The Fano factor approaches an asymptotic value of 0.16 at T=2 keV. Our results are consistent with experimental results.