Experimental Determinations of Resonant Raman Scattering Cross-Sections for Several Elements and Compounds

HECTOR JORGE SANCHEZ; M.C. VALENTINUZZI; C. A. PÉREZ; J. ABRAHAM

Arica (Chile)

Congreso; SARX 2006; 2006

X ray fluorescence spectra present singular characteristics produced by the different scattering processes. When atoms are irradiated with an incident energy lower and close to an absorption edge, scattering peaks appear due to an inelastic process known as resonant Raman scattering. It constitutes an important contribution to the background of the fluorescent line. There are different kinds of resonant Raman scattering depending on which shell of the atom the vacancy is created: KL-RRS, KM-RRS, LM-RRS. The resonant Raman effect must be taken into account in the determination of low concentration contaminants, especially when the elements have proximate atomic numbers. The values of the mass attenuation coefficients experimentally obtained when materials are analyzed with monochromatic x ray beams under resonant conditions differ from the theoretical values (between 5% and 10%). This difference is due, in part, to the resonant Raman effect. Detailed experimental measurements of the RRS and the involved parameters (i.e. cross sections) are scarce. Studies on the KL-RRS cross sections for elements as Cr, Mn, Fe, Ni, Cu, Zn using conventional x ray tubes with a monochromator and synchrotron radiation have been published. There have also been measurements of KL and KM-RRS cross sections with proton induced monochromatic x ray beams. In addition, KL-RRS cross sections were considered in studying Al impurities on Si. Finally, studies on the KL-RRS and LM-RRS cross sections for Yb, Lu and Hf have been reported. In this work, monochromatic synchrotron radiation was used to study the KL resonant Raman scattering on pure samples of Mn, Fe, Cu and Zn and on Mn2O3, CuO and Cu2O compounds.  Energy scannings were carried out in different ranges of energies near the absorption edge of the target element. As the Raman peak has a non-symmetric shape, theoretical models for the differential cross section, convoluted with the instrument function, were used to determine the RRS cross section as a function of the incident energy. For all the targets, the KL-RRS cross sections obtained increase as the incident energy approaches to the K edge energy, in agreement with the theoretical predictions. The measured cross sections for each sample were fitted to an expression with the functional form of the theoretical cross section; then, by interpolation it is possible to determine the RRS cross section for any incident energy. Since the Raman scattering can contribute considerably to the attenuation of x rays in matter and can interfere with XRF spectrometry, it is very important to understand the behavior of this process and quantify its occurrence probability.