Near-edge elastic photon scattering in amorphous systems R.P. Hugtenburg a,b, * , D.W. England b , D.A. Bradley c a School of Physics and Astronomy, University of Birmingham, B15 2TT, UK b Queen Elizabeth Medical Centre, University Hospital Birmingham, B15 2TH, UK c Department of Physics, School of Electronics & Physical Sciences, University of Surrey, GU2 7XH, UK Available online Abstract The structure of valence and unoccupied electron orbitals and the neighbouring electron density distribution of atoms and ions in amorphous systems can be examined through use of resonance in the elastic photon scattering-cross-section in the vicinity of core atomic orbital energies. So-called anomalous X-ray scattering (AXS) is a mode of analysis that offers similar information to that of EXAFS but can be obtained concurrently with diffraction mode imaging. Of interest is whether the dilute-ion aqueous system provides an environ- ment suitable for testing independent particle approximation (IPA) predictions. With the aqueous environment as the reference system for calibrating relative cross-sections, particular challenges include photons scattered by the medium being subsequently absorbed by the ion, limiting the thickness of the attenuating medium and motivating use of bright synchrotron photon sources where tunable X-rays are obtained at sub-eV resolution using a Si 111 monochromator. Measured scattering intensities and fluorescent yields were compared and shown to agree qualitatively with Monte Carlo calculations utilising amplitudes calculated from modified form-factors with anomalous scatter factors at a resolution of several eV determined from the Dirac–Slater exchange potential. Experimentally determined form-fac- tors for pure water were used to calibrate fluorescent yield and elastic scattering intensities for measurement of the energy dependent variation of these quantities near edge and XRF imaging of the Zn concentration in wax mounted, formalin fixed, breast tumour sam- ples. Results indicate the distribution of Zn at higher resolution than sampling dimensions used in previous studies. Shifts in the position and profile of K-edge absorption and elastic scattering features in aqeuous Zn, Zn doped sol–gel glass and Zn in tissue are shown to reflect changes in the atomic charge state and environment and offer support for the presence of non-nutrient Zn bearing components at elevated concentrations in tumour, of which the matrix-metalloprotein MMP-II is a likely contender. Ó 2007 Elsevier B.V. All rights reserved. PACS: 32.80.Cy; 87.54.Gb Keywords: Anomalous scattering; Near-edge; Trace elements 1. Introduction X-ray fluorescence (XRF) and anomalous elastic scat- tering (AXS) [1] offer complementary information that can be used to determine elemental abundances as well as charge state and environment of trace constituent atoms in biological systems. Synchrotron based XRF (e.g. micro-SXRF) currently offers high resolution mapping of the concentration of trace elemental components in sam- ples and, in particular, provides a new window on biolog- ical systems involving metals. Through the dispersion effect, variation in the absorption cross-section leads to scattering interference terms that are characterised by rapid variation in the elastic scattering signal close to the atomic orbital edges. We consider the impact of calibration meth- ods used in XRF, diffraction enhanced imaging (DEI) and species and environment sensitive scattering techniques such as AXS where, with increasing synchrotron bright- nesses, high resolution atom and environment specific map- ping is fast become a reality. 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.04.191 * Corresponding author. Address: School of Physics and Astronomy, University of Birmingham, B15 2TT, UK E-mail address: r.p.hugtenburg@bham.ac.uk (R.P. Hugtenburg). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B xxx (2007) xxx–xxx NIM B Beam Interactions with Materials & Atoms ARTICLE IN PRESS Please cite this article in press as: R.P. Hugtenburg et al., Near-edge elastic photon scattering in amorphous systems, Nucl. Instr. and Meth. B (2007), doi:10.1016/j.nimb.2007.04.191