Abstract. The absolute K-ionization cross sections of Ti and Ni by electron impact (impact energy__< 50 keV) was measured detecting the X-rays emitted by thin solid film targets of known mass thickness with a flow proportional counter. The experimental method, especially the correction procedures and the measurements are described, the results compared with calculations in different theoretical approaches. For impact energies above
Eo/EK>I.5 (EK=K-shell ionization energy) a systematic deviation of about +20%occurs in comparison with the best agreeing calculations of M.R.H. Rudge and S.B. Schwartz. A fit to Drawin's empirical formula reveals that the measurements are approximated better than _+ 10 % within the range of comparison.
Burhop's non relativistic result for the ionization cross section of the K-shell was recalculated. The remaining integrations over the change of momentum and the momentum of the ejected electron were done numerically especially for elements of low atomic number. The ionization function of the various elements normalized to unity at the maximum shows very small variation with atomic number. This universal behaviour of the ionization function was used to construct simple approximation formulae.
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