X-ray resonant Raman scattering on Ni employing polarized and unpolarized exciting radiation Ch. Zarkadas a, ⁎ , A.G. Karydas a , M. Müller b , B. Beckhoff b a Institute of Nuclear Physics, N.C.S.R. Demokritos, Aghia Paraskevi, 15310, Athens, Greece b Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, 10587, Berlin, Germany Received 29 July 2005; accepted 18 January 2006 Available online 2 March 2006 Abstract The X-ray resonant Raman scattering effect on nickel was studied by means of monochromatic polarized and unpolarized exciting radiation, respectively. Experiments involving polarized exciting radiation were carried out at the four crystal monochromator beamline of the Physikalisch- Technische Bundesanstalt for synchrotron radiation from 4 to 10 keV at the electron storage ring BESSY II. Resonant Raman spectra of thin Ni foils were recorded at the Cu-K α (8041 eV) exciting beam energy. In the Institute of Nuclear Physics of the N.C.S.R. Demokritos, the resonant Raman spectrum of a thick nickel target was also recorded for an unpolarized Cu-K α (8041 eV) exciting beam produced after the ionization of a thick Cu target by 1.7 MeV protons in a triaxial, orthogonal geometry. In the present work, the individual spectral characteristics and the methodological approaches adopted for the extraction of the Ni-RRS cross sections, with respect to each mode of excitation, are presented, compared and discussed. An excellent agreement was found between the Ni KL- RRS cross sections determined for polarized and unpolarized exciting radiation confirming the theoretical predictions within the experimental uncertainties achieved. © 2006 Elsevier B.V. All rights reserved. Keywords: Resonant Raman scattering; Nickel cross sections; Polarized radiation; Unpolarized radiation 1. Introduction The resonant Raman scattering (RRS) is an inelastic photon scattering process, which exhibits a strong resonant behavior as the energy of the incident exciting radiation approaches from lower energies to the absorption edge of a target element. In the literature, the RRS effect has been described as a two-step process, including an initial state, an intermediate state and a final state [1–5]. In the intermediate state, a virtual hole is created in an inner shell and the corresponding electron is excited to an unoccupied state. Subsequently, the hole is filled by a higher shell electron, followed by the emission of a photon. Thus, the final state includes a hole in a higher shell, a scattered photon and an electron, either in the continuum or in a bound excited state [6,7]. However, in the case of metallic targets, for which the discrete energy states merge into energy bands, the experimental discrimination of the two modes of electron excitation is possible, only by means of high-resolution spectrometers [6]. The conservation of energy between the initial and the final state requires that the available energy difference E 0 - U i (E 0 is the energy of the incident photon and U i is the binding energy of the inner shell with the hole in the final state) is distributed between the excited electron (having a kinetic energy of T e ) and the emitted scattered photon of energy E s . Depending on the shells in which the holes are located during the intermediate and the final state of the process, the RRS emission spectrum displays different continuous bands in an analogous manner with the discrete fluorescent emission lines following an inner shell photo ionization. Different types of the RRS process have been experimentally distinguished so far, such as the KL-RRS (with a virtual K-shell hole in the intermediate state and a L-shell hole created in the final state), the KM-RRS [8], KN-RRS [9], LM-RRS [10], etc. A schematic representation of the KL-RRS is shown in Fig. 1. Spectrochimica Acta Part B 61 (2006) 189 – 195 www.elsevier.com/locate/sab ⁎ Corresponding author. Tel.: +30 210 6503524; fax: +30 210 6511215. E-mail address: zarko@inp.demokritos.gr (Ch. Zarkadas). 0584-8547/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2006.01.002