Absolute CKx-ray production cross sections for 18-26-MeV protons on thin carbon foils

Absolute C $K$ x-ray production cross-section measurements using 18-26-MeV protons on thin carbon foils extend the range of previous measurements in the asymptotic region. These measurements permit extraction of the two main parameters of the asymptotic theory, viz., $M_{\mathrm{tot}}^2=0.84\mathrm{}$ and $C_{\mathrm{tot}}=8.2\mathrm{}$, which are in good agreement with those obtained in previous work at lower energies. The ionization cross sections extracted from these measurements are compared with the predictions of the asymptotic theory as well as the binary-encounter, semiclassical, and plane-wave Born approximation theories.