Theoretical model for bremsstrahlung isochromat spectroscopy: Application to metallic lanthanum

Recently, Riehle has reported bremsstrahlung isochromat measurements on Ba, La, and Ce showing linelike structures attributable to the empty $4f$ states above the Fermi edge. In the case of La, the energy dependence of the isochromat structure was examined for arbitrarily selected isochromat energies between 136 and 1860 eV; the intensity of the line-like structure relative to the remaining intensity exhibited strong variation in this energy range. To explain this phenomenon, the electron scattering mechanism used by Wendin and Nuroh to account for the appearance potential spectra of Ba, La, and Ce is applied to bremsstrahlung isochromat spectroscopy as well.