A. Knöchel

Use of microscopic XRF for non‐destructive analysis in art and archaeometry

The various application possibilities of microscopic x-ray fluorescence and associated methods for the characterization and provenance analysis of objects and materials of cultural heritage value are discussed by means of a number of case studies. They include the trace analysis of historic glass, the analysis of corroded coins and statues in bronze and silver and the study of inks on historical documents. These studies are conducted by means of micro-XRF instruments installed at synchrotron beamlines and by means of laboratory equipment, some of which is easily transportable to the museum or archaeological site where the objects of interest are located. Copyright

A submicron synchrotron x-ray beam generated by capillary optics

Abstract A novel capillary optics technique for focusing synchrotron X-ray beams has been applied in an experiment performed at the DORIS storage ring at HASYLAB. This new technique, which utilizes the total reflection properties of X-rays inside small capillaries, has recently been applied to generate beams of X-rays, with a beam size down to about 10 μm using conventional X-ray tubes. The result from our recent experiment shows that capillary optics can also be used to generate a submicron beam of X-rays from a synchrotron light source. A description of the capillary unit, and the alignment procedure is given. The influence of the thermal load on the device caused by the intense flux of synchrotron radiation will be discussed. Future perspectives of the capillary technique as applied to synchrotron radiation will be discussed.

Burbankite, a (Sr,REE,Na,Ca)-carbonate in fluid inclusions from carbonatite-derived fluids: Identification and characterization using Laser Raman spectroscopy, SEM-EDX, and synchrotron micro-XRF analysis

Abstract Burbankite, ideally (Na,Ca)3(Sr,REE,Ba)3(CO3)5, is a rare REE carbonate mineral that until now had been encountered only at a few localities including highly alkaline silicate rocks, carbonatites, and lacustrine sediments. It was identified as an abundant solid phase in fluid inclusions that represent fluids derived from the Kalkfeld carbonatite complex (Namibia). Burbankite occurs in association with other solids including nahcolite, halite, sylvite, rouvilleite (?), fluorite, calcite, cryolite, base metal sulfides, and phosphates. The carbonatite-derived fluids were trapped in quartzite country rocks close to the carbonatite contact. The optical and geochemical identification of burbankite has been confirmed by confocal Laser Raman spectrometry. The burbankite crystals show a Raman shift at 1078 cm-1, which is significantly displaced relative to peaks for other common carbonates and is much broader. The elemental composition of burbankite was determined by a combination of SEMEDX on opened inclusions and synchrotron-XRF analysis on unopened wafers. The SEM-EDX analyses of the burbankite crystals yielded a compositional range (in wt%) of Na2O 10.6-17.5, CaO 3.6-17.4, SrO 12.0-26.7, BaO 2.5-5.5, La2O3 3.5-7.0, Ce2O3 4.7-9.0, Nd2O3 0.9-2.1, and CO2 (calc.) 29.8-35.2. The Na/Ca ratios are between 1.0 and 4.3, which is high in comparison with rock-forming burbankite occurrences, and clearly distinguishes the burbankite crystals from carbocernaite. Synchrotron micro-XRF spectra yielded REE patterns decreasing from La to Yb over 2.5 orders of magnitude with small negative Eu anomaly [(Eu/Eu*)cn = 0.5-1.0] in some cases. The Y/Ho ratios range from 1 to 5, and Th/U ratios are between 1 and 10. The fluids trapped are interpreted to represent a highly evolved but pristine, alkali-rich, hydrous, carbonate melt, which had not lost alkalis to the country rocks by fenitization processes. The common occurrence of burbankite crystals in the fluid inclusions shows the high capability of carbonate melts and fluids to transport high-field-strength and large-ion-lithophile elements.

A New Type of Metalloprotein: The Mo Storage Protein from Azotobacter vinelandii Contains a Polynuclear Molybdenum–Oxide Cluster

Azotobacter vinelandii is a diazotrophic bacterium characterized by the outstanding capability of storing Mo in a special storage protein, which guarantees Mo‐dependent nitrogen fixation even under growth conditions of extreme Mo starvation. The Mo storage protein is constitutively synthesized with respect to the nitrogen source and is regulated by molybdenum at an extremely low concentration level (0–50 nM). This protein was isolated as an α4β4 octamer with a total molecular mass of about 240 kg mol−1 and its shape was determined by small‐angle X‐ray scattering. The genes of the α and β subunits were unequivocally identified; the amino acid sequences thereby determined reveal that the Mo storage protein is not related to any other known molybdoprotein. Each protein molecule can store at least 90 Mo atoms. Extended X‐ray absorption fine‐structure spectroscopy identified a metal–oxygen cluster bound to the Mo storage protein. The binding of Mo (biosynthesis and incorporation of the cluster) is dependent on adenosine triphosphate (ATP); Mo release is ATP‐independent but pH‐regulated, occurring only above pH 7.1. This Mo storage protein is the only known noniron metal storage system in the biosphere containing a metal–oxygen cluster.

Analysis of Ni on Si-wafer surfaces using synchrotron radiation excited total reflection X-ray fluorescence analysis

Abstract Total Reflection X-Ray Fluorescence Analysis excited with synchrotron radiation (SR-TXRF) monochromatized by a multilayer (ML) has been used for the analysis of Ni on Si-wafer surfaces. Intentionally contaminated wafers using droplet samples have been used to determine the detection limits. Two different kinds of the geometrical arrangement of sample and detector have been compared, one of them resulting in detection limits of 13 fg for Ni. Experiments have been performed at Hasylab, Beam L using a bending magnet radiation.

TXRF with synchrotron radiation Analysis of Ni on Si-wafer surfaces

Abstract SR-TXRF (Synchrotron Radiation excited Total Reflection X-ray Fluorescence Analysis) with monoenergetic radiation produced by a W C multilayer monochromator has been applied to the analysis of Ni on a Si-wafer surface. An intentionally contaminated wafer with 100 pg has been used to determine the detection limits. 13 fg have been achieved for Ni at a beam current of 73 mA and extrapolated to 1000 s. This technique simulates the sample preparation technique of Vapour Phase Decomposition (VPD) on a wafer surface.

Total Reflection X‐Ray Fluorescence Analysis Excited by Synchrotron Radiation (SR‐TXRF): Variation of Excitation Conditions and Sample Geometries

The use of synchrotron radiation as the excitation source for total reflection x-ray fluorescence analysis (SR-TXRF) in combination with a multilayer structure for monochromatization led to detection limits in the femtogram range for medium-Z elements. Experiments were performed at the Hasylab Beamline L using bending magnet radiation. Different methods for the modification of the spectral distribution, viz. multilayer monochromatization, insertion of a high-energy cut-off and a simple filter technique, were compared. Also, several possible types of geometrical arrangement of the sample and detector were examined to establish whether an improvement in excitation or detection conditions is possible. Samples were of evaporated droplets of aqueous or acidic solutions of several elements at various concentrations. Spectra were evaluated and the data used to extrapolate the detection limits (DL). Monochromatization of the synchrotron radiation in combination with a sample carrier positioned in the vertical plane and a side-looking detector in the plane of polarization turned out to give the best results with a DL of 15 fg for Ni.

Use of lead-glass capillaries for micro-focusing of highly-energetic (0–60 keV) synchrotron radiation

The performance of ellipsoidally shaped lead-glass capillaries for focusing the polychromatic synchrotron beam produced by a bending magnet of the DORIS positron storage ring (Hasylab, Hamburg, Germany) is discussed. The size, intensity and energy distribution of the focused beam produced by such capillaries are compared with those of beams generated by means of straight borosilicate capillaries, indicating that beam sizes ofca. 4 µm at the sample surface can be obtained with a total flux density that is ca. ten times higher than when a collimated beam is employed. Synchrotron radiation with energies up to 60 keV is focused, leaving the original energy distribution of the white synchrotron beam virtually unchanged. The analytical characteristics of the µ-XRF set-up at Beamline L of Hasylab, when equipped with a lead-glass capillary, were investigated by means of NIST SRMs and indicate that interference-free absolute/relative detection limits in the 1–10 fg/0.8–2 ppm range are achievable from 100 µm silicate-type samples for the elements from Mn (Z=25) to Gd (Z=64) using their Kα lines within 1000 s counting time. Elemental yields are situated in the 10–100 counts s–1 per 100 mA per (µg cm–2) range. As illustrations of the type of investigations these highly energetic, micrometre-sized beams make possible, the two-dimensional mapping of the distribution of REEs (rare earth elements) and other heavy elements in geological igneous rock samples and the three-dimensional non-destructive analysis of heavy metals (such as V, Fe, Ni and Mo) in individual fly-ash particles by means of fluorescence microtomography are briefly described.

New developments of X-ray fluorescence analysis with synchrotron radiation (SYXFA)

Abstract The method of X-ray fluorescence analysis with synchrotron radiation was developed in two different directions. The high intensity and small divergence of the source were used for developing a scanning device (microprobe) with high resolution (≈ 10 μm ) and absolute limits of detection in teh range of 10 −14 g. For improving the relative limits of detection and selective excitation, monochromatization by a graphite crystal was tested. First applications for both methods are demonstrated.

X-ray fluorescence analysis with synchrotron radiation

The method of trace element analysis by X-ray fluorescence detection has been improved to an especially efficient multielement method for the ng to pg range in matrices containing light elements by the use of synchrotron radiation for excitation. It was necessary to determine the intensity and polarisation of the synchrotron radiation quantitatively. Inclusion of the vertical electron beam diameter and the divergence into the calculation, and definition of an effective vertical beam diameter by fitting the calculated polarisation spectrum leads to quantitative agreement between experimental and calculated absolute intensity spectra of scattered and fluorescent radiation of well-defined samples. This means that absolute mass determinations are in principle possible. The physical limits of detection calculated with these data agree very well with the experimental results. The limits of detection for special elements can be optimised by using different absorbers in the primary beam. They range from 0.05 to 0.2 μg for organic matrix. This implies an absolute physical detection limit of 0.1 to 0.4 pg for a diameter of the primary beam of 0.5 mm and a sample of 1 mg/cm2.