X-ray continuum from thick elemental targets for 10–50-keV electrons

The x-ray continuum from thick elemental targets was investigated from 1–10 Å using a crystal spectrometer and electron energies of 10–50 keV in an electron probe microanalyzer. Experimental results corrected for absorption, atomic number, and stray radiation agreed well with theoretical calculations based on Sommerfeld's cross section and Bethe's retardation law. The calculations used an improved version of the empirical formula of Kirkpatrick and Wiedmann for the cross section. Theory and experiment agreed best for J = 11.5Z in Bethe's law, but taking account of known inaccuracies in the Sommerfeld cross section, the Berger-Seltzer values are recommended. Results did not verify the linear atomic number dependence of the Kulenkampff-Kramers equation; for fixed electron energy E0 and photon energy Ev the intensity varied as Zn, where n ranged from 1.18 to 1.38 depending on Z, E0, and Ev. For fixed Z and Ev the intensity varied approximately as (E0 − Ev). Agreement of theory and experiment indicated that the correction procedures commonly used for characteristic lines can be applied to the continuum but the atomic number correction using Duncumb and Reed's procedure differed for the continuum compared to that for characteristic lines. Absorption correction using f(χ) of Andersen and Wittry gave good results for f(χ)≥0.4 but lower values could not be conclusively tested because of errors due to stray radiation which is shown to be caused by electrons backscattered from the specimen. Nevertheless, it was possible to use the Z dependence of the continuum to estimate certain mass absorption coefficients.