The Ionization Loss of Energy of Fast Charged Particles in Gases and Condensed Bodies

The ionization loss of particles is treated, taking into account the polarization properties of the medium traversed. The medium is characterized by a general expression for a complex dielectric constant containing $n$ different types of dispersion electrons, and one type of conduction electrons. Damping effects are not neglected but turn out to be significant for conduction electrons only. Formulae for the reduction in loss compared with the Bethe-Bloch expression for independent atoms, are derived and quantitatively discussed for the cases of physical interest. It is shown why qualitative and large quantitative differences occur in the results of the present multi-frequency theory compared with earlier work in which only a single dispersion frequency was assumed. Curves are given for a number of substances to show the reduction in energy loss for a wide range of momenta of the incident particles, the theory applying to all types of particles in the proper velocity range. A quantitative discussion is given which shows good agreement of the multifrequency theory with those experiments which at present allow quantitative evaluation.