Mean Free Path for Plasmon Excitation in Aluminum in the Energy Region from 1.5 to 10.9 keV

The mean free paths for plasmon excitation were measured through the observation of the energy loss spectrum of the electrons which passed through a thin aluminum film. In order to obtain accurate values the following problems of a thin film were discussed in detail; the thickness determination, the evaluation of the microscopic thickness variation in a film and the estimation of the effect of the surface contamination and the oxidation. The influence of the angular dispersion of the electrons due to plasmon excitation was found to be very serious. The agreement of the observed value with the Quinn's theory was considerably good in the energy region from 5 to 10.9 keV and in the lower region the observed paths were found to be longer.