Hoszowska, J.Kheifets, AnatoliDousse, Jean-ClaudeBray, IgorCao, W.Fennane, K.Kayser, Y.Kavcic, M.Szlachetko, J.Szlachetko, M.2015-12-071742-6596http://hdl.handle.net/1885/20665The photon energy dependence of the double K-shell ionization of light atoms is reported. Experimental double-to-single photoionization cross section ratios for Mg, Al, Si and Ca were obtained from measurements of high-resolution x-ray emission spectra. The double photoionization (DPI) cross-sections for K-shell hollow atom production are compared to convergent close-coupling calculations (CCC) for neutral atoms and He-like ions. The relative importance of the initial-state and final-state electron-electron interactions to the K-shell DPI in many-electron atoms and two-electron ions is addressed. Physical mechanisms and scaling laws of the K-shell double photoionization are examined. A semiempirical universal scaling of the DPI cross sections with the effective nuclear charge for neutral atoms 2≤Z≤47 is established.Keywords: Convergent close-coupling calculations; Cross section; Double photoionization; He-like ions; High resolution; Hollow atoms; K-shell ionization; K-shells; Light atoms; Many-electron atoms; Neutral atoms; Nuclear charges; Photon energy; Physical mechanism;201010.1088/1742-6596/212/1/0120062016-02-24