Seminars Archive

Synchrotron Radiation X-Ray Fluorescence Analysis: a versatile technique

Abstract
Synchrotron radiation is an ideal source for x-ray fluorescence analysis and can be successfully employed in many different configurations and for diverse purposes. Some applicative examples making use of various acquisition geometries and set-ups will be presented to demonstrate the versatility of the technique and the possibilities it offers. Total Reflection X-Ray Fluorescence Analysis exploits a grazing incidence excitation geometry to enhance surface sensitivity. It can be used for the elemental analysis of small amounts of samples deposited on polished carrier, contamination on surfaces or for the study of the near surface region of a bulk sample.  At HASYLAB Beamline L SR-TXRF was implemented for trace analysis in different geometries and energy ranges to discover the set-up leading to the lowest detection limits. XANES with TXRF acquisition was adopted for the speciation of arsenic in the xylem sap of cucumber plants, and the technique could be successfully applied for concentrations down to 30 ng/mL of As. Results showed that the xylem sap of cucumber plants grown in a nutrient solution where As(V) had been added, contained a high percentage of As(III), indicating that a reduction of the As has taken place at root level. The phenomenon of self absorption for XAS with TXRF acquisition is currently under investigation. Recently a vacuum chamber has been built for HASYLAB Beamline L with a sample changer for routine analysis. EXAFS measurements on As implants into silicon wafers for the formation of Ultra Shallow Junctions was carried out at the RelfEXAFS station of the GILDA beamline at the ESRF. Samples were illuminated at grazing incidence at different angles and the fluorescence acquired in order to gain structural information from the only near surface layer (about 3 nm) or the entire implant. Micro X-Ray Fluorescence Analysis adopts a micro-beam obtained by collimation or focussing x-ray optics to provide spatially resolved information on the elemental distribution (imaging) by scanning the sample relatively to the beam. As an example the application of the technique to the study of Pb storage in human articular bone will be shown. Cross sections of hip heads and patellas were analysed at the microfocus end-station of HASYLAB Beamline L, where the monochromatic beam is focussed with a polycapillary optic. First experiments were carried out with thick (5 mm) samples and an accumulation of Pb was found in the proximity of the cortical bone. The lateral resolution was affected by the thickness of the sample and the 45° excitation geometry adopted. Hence, Confocal Micro X-Ray Fluorescence allowed the 3D imaging of thick specimen with a spatial resolution of 15-20 µm. The measurements showed clearly that Pb accumulates predominantly at the tidemark, the calcification front between calcified and articular cartilage. Micro XANES experiments were carried out to investigate the molecular structure of the accumulated Pb. First measurements indicate that Pb is mainly incorporated into hydroxyapatite, as it is in the bone structure.