Threshold studies of a multivacancy process in theKβregion of argon

Threshold-region measurements are reported for the production of single-vacancy and multiple-vacancy configurations of atomic argon by monochromatic x-ray photons in the region of the $1s$ ionization threshold. The experiment used monochromatized synchrotron radiation produced in the six-pole wiggler at the Stanford Synchrotron Radiation Laboratory with 3.2-GeV electrons at circulating currents of 20-30 mA. Secondary radiation including elastically and inelastically scattered radiation as well as fluorescent spectra were analyzed in a focusing spectrometer with a linear position-sensitive detector. Fluorescent spectra in the $K\beta$ region were modeled by inclusion of spontaneous decay of double-vacancy configurations of the type $\mathrm{KM}\to M^2$. This multiplet model permitted extraction of partial cross sections for the production of ${\mathrm{KM}}_{\mathrm{I}}$ and ${\mathrm{KM}}_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ configurations. This report also contains new data on details of absorption fine structure in the region of the single-vacancy threshold and the principal double-vacancy thresholds.