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 Kβ region were modeled by inclusion of spontaneous decay of double-vacancy configurations of the type KM→M². This multiplet model permitted extraction of partial cross sections for the production of KMI and KMII,III 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.