X-ray hypersatellite spectra of hollow atoms

The K^hα_1,2 and K^hβ _1,3 hypersatellites (HS), originating in transitions with a double K vacancy as the initial state, have been studied using photoexcitation by monochromatic synchrotron radiation. High-resolution emission spectra, their excitation energy threshold and their evolution with the exciting photon energy from threshold to saturation have been measured for a range of elements. The analysis, done in conjunction with ab initio Dirac-Fock calculations including QED corrections, reveals a good overall agreement between the theory and the experiment. However, small deviations are found, and assigned to an incomplete accounting for the intermediacy of the coupling scheme. The incident-photon energy dependence of the cross-section suggests a pure shake-off (SO) process for the creation of the second K hole in all measured elements. The intensity evolution deviates significantly from the predictions of the regnant theoretical model of Thomas and has a surprisingly large saturation range, which still lacks a theoretical explanation.