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The Khα1,2 and Khβ1,3 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. [Copyright &y& Elsevier]

Abstract: Inter- and intra-shell electronic correlations in an atom are manifested in, and can be studied through, the X-ray emission spectra of multielectronic transitions. We have measured the spectra of Khα1,2 hypersatellites (HS), Kα3,4 satellites (S), and the 3d electron shake-up satellites (D) accompanying the Kα1,2 diagram lines, and their evolution from the double-ionization threshold, for selected 4- and 5-row elements of the periodic table. These spectra originate in the [1s]−1, [2p]−1, and [3d]−1 spectator two-electron transitions [1s]−2→[1s2p]−1, [1s2p]−1→[2p]−2, and [1s3d]−1→[2p3d]−1 respectively. Photoexcitation by monochromatized synchrotron radiation together with high-resolution crystal spectrometers were employed. Ab initio relativistic multiconfigurational Dirac–Fock (RMCDF) calculations reproduce the spectra very well for all transitions, with the HS spectra showing a strong dependence on QED effects. The excitation thresholds were determined accurately. The threshold-to-saturation energy range of the intensity was found to depend strongly on the principal quantum number n of the spectator hole. For example, for Cu, ranges of 2%, 10%, and 60% of the threshold energy are found for the D, S and HS spectra, respectively. Only the D spectrum''s evolution conforms to the Thomas model, indicating a dominant shake up/off process. The S and HS spectra seem to be dominated by the knockout (“two-step-one”) process near threshold. The S spectra show a two-regime behavior. Near threshold both shape and intensity vary with excitation energy, and above that only intensity changes are observed. The lower-than-expected Khα1/Khα2 intensity ratio found for Z=23–30 and 39–46 indicates that the angular momenta coupling scheme at the regime intermediate between the LS coupling at low-Z and the jj coupling at high-Z may not be fully accounted for by the prevailing theory. [Copyright &y& Elsevier]

The X-ray solar monitor (XSM) is a calibration instrument of the demonstration of compact imaging X-ray spectrometer (D-CIXS) experiment, with a separate Silicon detector unit on the SMART-1 spacecraft. The non-imaging HPSi PIN sensor has a wide field-of-view (FOV) to enable Sun visibility during a significant fraction of the mission lifetime, which is essential for obtaining calibration spectra for the X-ray fluorescence measurements by the imaging D-CIXS spectrometer. The energy range (1–20 keV), spectral resolution (about 250 eV at 6 keV), and sensitivity (about 7000 cps at flux level of 10−4 W m−2 in the range 1–8 A˚) are tuned to provide optimal knowledge about the Solar X-ray flux on the Lunar surface, matching well with the activating energy range for the fluorescence measured by D-CIXS. The independent science of the XSM will also be valuable, since the XSM energy range is very sensitive to solar flares. The countrate during the top of an X1 flare will be about 35 times higher than the average quiescent countrate at solar maximum. The relative increase will be the same for an M1 flare during the SMART-1 mission, which will be closer to the next solar minimum. Since the XSM will observe the Sun as a star, and the energy range and spectral resolution are close to those of present astronomical X-ray satellites (e.g., XMM-Newton, ASCA, Chandra), we will obtain an X-ray database of the Sun which can be related with the stellar X-ray observations more easily than the data from present solar X-ray instruments. In this publication we give a detailed description of the design, performance, and tasks of the XSM instrument, and view the science perspectives. [Copyright &y& Elsevier]