K-shell x-ray production cross sections and KP/Ka ratios are presented for 0.6to 2.4-MeV protons and alpha particles incident on thin targets of selected elements from Nb to Gd. The KP/Ka ratios are compared to the theoretical predictions of Scofield and agree within 10%. The experimental cross sections are compared to the theoretical predictions of the plane-wave Born approximation (PWBA) and the PWBA modified to include binding energy, Coulomb deflection, and relativistic effects. It is seen

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... hat the PWBA modified for binding energy and Coulomb deflection effects agrees with the experimental data for Nb to within uncertainties, but its predictions are lower than the data by larger amounts as the target Z increases. Inclusion of an ad hoc semiclassical relativistic correction to the theoretical cross section, as suggested by Hansen, improves the agreement with the data, but overestimates the data for the highest-Z elements,