Mean Excitation Potential of Light Compounds

The mean excitation potentials $I$ of Al, Si, ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$, Si${\mathrm{O}}_2$, and ${\mathrm{C}}_5$ ${\mathrm{H}}_8$ ${\mathrm{O}}_2$ were determined to an accuracy of ±0.5% by fitting theoretical range functions to experimental energy-loss data. The $I$ values for the compounds were found to be 7 to 11% larger than the corresponding values calculated for mixtures using Bragg's rule.