Core thresholds in alkali metals

The Na $L_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ core threshold and the K $M_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ core threshold have been examined using the Princeton inelastic-electron-scattering spectrometer. Spectra were acquired at several momentum-transfer values for each threshold. The threshold shapes are peaked at zero momentum transfer and become more rounded as momentum transfer is increased. We analyze these data with respect to the Mahan-Nozières-De Dominicis (MND) theory of core thresholds. We compare the results of this analysis to the results published by other experimenters. We conclude that the momentum-transfer dependence of core threshold shapes that we see in these data and in the Mg $L_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ data previously published is very likely to be the result of the many-body effects described by the MND theory.