Scattering of X‐rays near the K absorption edge II. Dispersion factors f′ and f″

Abstract

BY Dispersion Factors f' and P. SUORTTIThe dispersion factors of the X-ray scattering amplitude, f' and f", are studied in the dipole approximation where they are independent of the scattering angle. The imaginary part is proportional to the absorption coefficient, and below the Kedge the observed fs is in a close agreement with the value calculated from the resonant Raman cross-section. The real part is calculated from the tabulated absorption coefficients in a number of cases where comparison with direct determinations off' can be made. The agreement is good. particularly when extensive data near the edge are available, while recent theoretical values are consistently low. Calculated values of f' are tabulated for transition elements a t several commonly used X-ray wavelengths.Die Dispersionskorrekturen f' und f" der Rontgenstreuamplitude werden in der Dipolnaherung, wo sie unabhangig voni Streuwinkel sind, untersucht. Der Irnaginarteil ist proportional zum Absorptionskocffizienten. Unterhalb der K-Absorptionskante ist der gefundene Wert von fg in guter Ubereinstimrnung mit dem theoretischen, aus dem resonanten Ramanwirkungsquerschnitt berechneten Wert. I n mehreren Fallen, in denen der Vergleich rnit direkt bestiinmten f' moglich ist, nird der Rcalteil aus den in Tabellen gegebenen Absorptionskoeffizienten berechnet. Die Ubereinstimmurig ist gut, besonders, wenn zahlreiche Werte in der Nahe der Kante vorhanderi sind, wdhrend neuere theoretische Werte systematisch zu niedrig sind. Fur die Ubergangselemente nerden die berechneten Werte von f' fur mehrere allgemein benutzte Wellenlangen tabelliert. IntroductionThe resonant response of an atom to X-rays is seen in the alniost singular changes of scattering and absorption near an absorption edge. Fluorescence and the resonant Raman scattering (RRS) is treated in the preceding paper [l]. Both phenomena are covered by a single formula for the cross-section, and there is a continuous change froin the RRS to the full fluorescence.The coherent scattering near an absorption edge is affected by the resonant phenomena as well. The drastic changes in the atomic scattering factor provide an effective tool in the crystal structure analysis; this rapidly developing field has been recently reviewed l i e

Scattering of X‐rays near the K absorption edge I. Fluorescence and resonant Raman scattering in transition metals

“…The TDS crosssections were taken from a recent calculation [9], and for the KP radiations these were changed by f$/f; where the subscripts of the atomic scattering factors refer to the radiations. Experimental values of fi/fi were used [21]. The Compton and plasmon cross-section remain unchanged.…”

XANES in doped radiosensitive glasses

“…Given its ability to show the resonant intermediates as well as chemical shift of the K-edge energy with increasing charge, XANES can be used to determine charge state, including mixed charged states, of a given species within a material. Experiment and theory (Suortti, 1979;Nakai et al, 1998) suggest that XANES can be measured in a fluorescence mode, enabling more accurate characterisation of the sample. This is the mode of measurement employed herein.…”