We present the first observation of the 1s2p 3 P2 → 1s2s 3 S1 transition in He-like uranium. The experiment was performed at the internal gas-jet target of the ESR storage ring at GSI exploiting a Bragg crystal spectrometer and a germanium solid-state detector. Using the 1s 2 2p 2 P 3/2 → 1s 2 2s 2 S 1/2 transition in Li-like uranium as reference and the deceleration capabilities of the ESR storage ring, we obtained the first evaluation of the energy of an intra-shell transition for a He-like heavy ion.
The development of a wavelength-dispersive spectrometer for microfluorescence analysis at the X-ray Microscopy ID21 beamline of the European Synchrotron Radiation Facility (ESRF) is reported. The spectrometer is based on a polycapillary optic for X-ray fluorescence collection and is operated in a flat-crystal geometry. The design considerations as well as operation characteristics of the spectrometer are presented. The achieved performances, in particular the energy resolution, are compared with the results of Monte Carlo simulations. Further improvement in the energy resolution, down to $ eV range, by employing a double-crystal geometry is examined. Finally, examples of applications requiring both spatial and spectral resolutions are presented.
The spectral distribution of the 1s2s {1}S{0}-->1s{2} 1S0 two-photon decay of He-like tin was measured using a novel approach at the gas-jet target of the ESR storage ring. Relativistic collisions of Li-like projectiles with low-density gaseous matter have been exploited to selectively populate the desired 1s2s state. Compared to conventional techniques, this approach results in a substantial gain in statistical and systematic accuracy, which allowed us to achieve for the first time a sensitivity to relativistic effects on the two-photon decay spectral shape as well as to discriminate the measured spectrum for Sn from theoretical shapes for different elements along the He-isoelectronic sequence.
Experimental evidence for the correlated two-electron one-photon transitions (1s À2 ! 2s À1 2p À1 ) following single-photon K-shell double ionization is reported. The double K-shell vacancy states in solid Mg, Al, and Si were produced by means of monochromatized synchrotron radiation, and the two-electron one-photon radiative transitions were observed by using a wavelength dispersive spectrometer. The two-electron one-photon transition energies and the branching ratios of the radiative one-electron to twoelectron transitions were determined and compared to available perturbation theory predictions and configuration interaction calculations.Understanding electron-electron interactions in ionization, excitation, and relaxation of many-body systems is one of the key issues of atomic physics. In this context of special interest are hollow atoms, i.e., atoms with empty innermost shells and occupied outer shells, because singlephoton double K-shell ionization is driven by multielectron interactions (see [1,2], and references therein), and the decay of K-shell hollow atoms involves electron correlation effects. Furthermore, hollow atom formation in ultraintense hard x-ray free-electron laser beams reveals electron dynamics on the femtosecond time scale [3].In response to a K-shell doubly excited state, electron relaxation and rearrangement processes follow. The excited atom decays in a cascade of nonradiative Auger and radiative transitions. The radiative decay of double K-shell hole states proceeds mainly through the oneelectron one-photon (OEOP) process, which corresponds to the K h ð1s À2 ! 1s À1 2p À1 Þ hypersatellite transition. In the few orders of magnitude weaker competitive decay channel, the two-electron one-photon (TEOP) transition K h ð1s À2 ! 2s À1 2p À1 Þ, the two K-shell core holes are filled simultaneously via a correlated two-electron jump and one photon is emitted (see Fig. 1). TEOP transitions are thus correlated multielectron processes which can be described only by many-electron models.Interest in TEOP transitions dates back to 1925. Predicted by Heisenberg [4], it was only 50 years later that the first experimental evidence for TEOP transitions in heavy-ion (HI) collisions was reported by Wölfli et al. [5]. Although the K h to K h branching ratio should not depend on the excitation mode, multiple electron ionization in HI collisions changes the electronic configurations and affects the intensities and energies of the measured transitions. Thus data from HI collision experiments show a wide spread of values [6][7][8][9][10], making comparison with theory often inconclusive. On the theoretical side, significant differences in the predicted TEOP radiative decay rates have been reported [11][12][13][14][15][16][17][18][19][20][21]. In this respect, photon impact data provide a more stringent test for atomic structure calculations. However, the single-photon double K-shell ionization cross sections are $10 3 smaller than in HI collisions. Thus photoionization experiments are more challenging, and, to t...
We report on the surface-sensitive grazing emission X-ray fluorescence technique combined with synchrotron radiation excitation and high-resolution detection to realize depth-profile measurements of Al-implanted Si wafers. The principles of grazing emission measurements as well as the benefits offered by synchrotron sources and wavelength-dispersive detection setups are presented. It is shown that the depth distribution of implanted ions can be extracted from the dependence of the X-ray fluorescence intensity on the grazing emission angle with nanometer-scale precision provided that an analytical function describing the shape of the depth distribution is assumed beforehand. If no a priori assumption is made, except a bell shaped form for the dopant distribution, the profile derived from the measured angular distribution is found to reproduce quite satisfactorily the depth distribution of the implanted ions.
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