W Jitschin

Coster-Kronig and fluorescence yields of Au L subshells derived from photoionisation measurements

Photoionisation studies provide a direct method for an accurate determination of vacancy decay parameters. The authors report on such measurements performed for the Au L shell. Thin Au foils were irradiated by photons with energies ranging from 11.5 to 15.2 keV. The mass absorption coefficient as well as the induced L X-radiation were measured. From the absorption coefficient the ionisation cross sections of the individual L subshells were derived. Comparison of the cross sections and the induced X-ray fluorescence gives Coster-Kronig factors, fluorescence yields and branching ratios for different X-ray lines. For the Coster-Kronig factors and fluorescence yields significant deviations from previously adopted values were found.

Fluorescence, Coster-Kronig and Auger yields of the 62Sm L subshells measured with the synchrotron photoionization method

Using monochromatized synchrotron radiation a sample of thin samarium and titanium foils was excited, and the induced Sm L X-rays and Ti K X-rays were detected by a Si(Li) detector. When the primary photon energy is tuned across the Sm L2 and L1 edges, the intensities of the Sm L X-ray lines normalized to the Ti K alpha intensity exhibit abrupt changes. From these intensity changes the Coster-Kronig factors were determined: f23=0.14+or-0.03, f13=0.18+or-0.03 and f12=0.19+or-0.03. The value of f13 is substantially smaller than predicted by theory and extrapolated from heavier elements. Furthermore, from the total intensities of all lines originating from the same Sm L subshell the ratios of the fluorescence yields omega 1/ omega 3=0.48+or-0.07 and omega 2/3=1.05+or-0.05 were obtained.

Polarisation of the proton-induced L X-radiation in 3d transition elements

The polarisation of the Ll X-ray line of 27Co, 28Ni, 29Cu and 30Zn targets induced by proton impact has been measured at ion energies ranging from 60 keV to 2.4 MeV. The polarisation is attributed to the collisionally induced alignment of the 2p3/2 vacancy. Measured polarisation values show strong dependence on the target nuclear charge. The small values found particularly in Co and Ni are attributed to a dealignment after the collision caused by angular momentum recoupling between the 2p3/2 vacancy and the partially filled 3d shell. For Cu and Zn the dealignment is expected to be small, and the collisionally induced alignment has been derived from the measured polarisation values. The experimental alignment data agree with the theory only qualitatively.

X‐ray and Auger‐electron yields for quantitative element analysis

Quantitative analytical work frequently relies on calibration measurements in which empirical parameters are determined whose interconnection to basic physical properties is unsatisfactory. In contrast, the fundamental processes of x‐ray absorption and emission are known with reasonable accuracy a priori and are insensitive to the state of matter. The present paper discusses recent results on these inner‐shell processes obtained with synchrotron radiation. Absorption cross sections show a smooth energy dependence by a power law; minor dispersion like deviations from this behavior due to electron correlations are now established. Precise x‐ray and Auger yields can be determined by a novel technique in which the fluorescence is detected for various primary energies in the realm of the absorption edges.

A compact plane-crystal X-ray spectrometer for ion-atom collision studies

An easily portable, compact crystal spectrometer is described which has been developed for accelerator-based experiments. The spectrometer was tested for x-ray energies ranging from 0.6 to 9 keV. The instrumental resolution is mainly determined by the X-ray angular collimation (0.07 degrees FWHM) and amounts to 800 at 45 degrees diffraction angle. Several spectra obtained by photon, electron and ion impact are presented.

Electron exchange in the Na 3p electron impact excitation

The 3s-3p impact excitation of spin-polarised Na atoms by unpolarised electrons has been studied. The fluorescence light emitted in the decay of the excited state exhibits linear polarisation caused by the collisional induced 3p alignment, as well as circular polarisation resulting from the spin orientation of the 3p electron at the time of the decay. Since the exchange interaction causes a spin flip, the degree of circular light polarisation is a measure for the contribution of the exchange channel to the total excitation cross section. At small impact energies where exchange becomes important, the authors found a decrease of the circular polarisation. They analysed the hyperfine coupling between the excited electron and the polarised nucleus, and calculated the light polarisation from theoretical excitation cross sections. Comparison of experiment and theory shows reasonable agreement.

The influence of multiple vacancies on inner-shell alignment measurements

Experimental studies of inner-shell alignment investigate the anisotropy or polarisation of emitted X-rays or electrons. In the case of a single vacancy the alignment can be derived from the measured anisotropy by well known formulae. In case of multiple vacancies the observed alignment may be different from the collisionally-induced alignment: post-collision interaction of the vacancies within their lifetimes may perturb the alignment. Examples are discussed and numerical values of the depolarisation caused by coupling with an isotropic spectator are given.