The Cu $K$ ionization cross section by electron impact has been measured in the energy range from the $K$-shell threshold to $90\mathrm{keV}$. To this end, a thin Cu film deposited on a thin C backing has been employed. The x rays emitted by the target have been detected by two silicon drift detectors placed at front and back angles with respect to the direction of the incident beam, which allowed us to better assess the peak fit procedure of the $K$ multiplet. A careful analysis of the Cu $K$ x-ray spectra generated by electron bombardment has been conducted, including not only the diagram lines but also the satellite lines and the counts that come from the radiative Auger effect. This enabled us to obtain the $K\alpha$ and $K\beta$ x-ray production cross sections with relative uncertainties of the order of $5\%$, and the $K$-shell ionization cross section with a precision around $7.5\%$. We show that, in most cases, the ionization cross sections reported according to current practice cannot be compared with the available theoretical calculations because the latter do not account for multiple-ionization effects. Our results agree with the distorted-wave Born approximation only when the $K$ x-ray counts from satellite lines, which amount to about $20\%$ of the total, are excluded.

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• Atomic spectra
• Electron & positron scattering
• Electronic excitation & ionization