Tube-excited energy-dispersive X-ray fluorescence analysis. II. Energy-dispersive X-ray fluorescence analysis of air particulate material.

The use of monoenergetic exciting radiation of molybdenum obtained with a secondary target set-up, a conventional water-cooled tungsten anode x-ray tube and a Si(Li) semiconductor detector permits many trace and minor constituents from chlorine to strontium to be determined in particulate material collected on cellulose filters. The method is rapid and economical compared to other multielement techniques. The use of one or more single-element thin-film standards to calibrate for the analysis of many elements appears to be possible, but some systematic errors must be prevented. Absorption of the fluorescent radiation is remedied by a simple correction method. The precision and the accuracy of the method were critically examined by independent analysis of a number of samples with instrumental neutron activation analysis and by interlaboratory comparisons on the same samples.     

Ultrafast selected energy x-ray absorption spectroscopy investigations of Ni and Zn species

The results of ultrafast selected energy x-ray absorption spectroscopy (USEXAS) investigations of Ni and Zn species are presented. The USEXAS measurements described here employed characteristic x-ray radiation of L(alpha) and L(beta) from an ultrafast laser-driven W x-ray target to probe the K absorption edges of Ni and Zn, respectively. Static x-ray absorption edge spectra of six Ni and Zn species in either solid or solution form were obtained. Simulations of near-edge x-ray absorption spectra of these Ni and Zn species were carried out with FEFF. The results of USEXAS measurements were in general agreement with the theoretically simulated spectra and those measured with synchrotron x-ray radiation.     

Rapid determination of chromium in natural waters by chemiluminescence with a centrifugal fast analyzer.

A secondary target tube excited x-ray fluorescence apparatus was compared with a conventional sequential wavelength dispersive spectrometer. Representative samples from the lead industry, an agglomerate for the lead production and a typical air particulate sample collected on cellulose filter were used in the comparison.The following factors were considered: resolving power, spectral interferences, intensity and peak-to-background ratio, sensitivity, reproducibility and precision. The energy dispersive method is advantageous for the multi-element analysis with limited precision of thin samples of environmental composition.     

Characteristics of radiation induced light in optical fibres for portal imaging application

The purpose of this paper is to characterize the radiation induced light in optical fibres to optimise the design of a new Cherenkov detector for portal imaging application in radiation therapy. Experiments were performed using a single optical fibre to evaluate the angle dependence, spectrum and temporal properties of the radiation induced light in the optical fibre in comparison with that of Cherenkov radiation. A theoretical model was also developed to compare with experiments. It has been found that radiation-induced light output from the optical fibre under megavoltage (MV) x-ray irradiation is significantly (about 45 times) higher than that under 100 kVp x-ray irradiation for the same dose rate at the fibre. The angular-dependence, spectrum and temporal properties of the radiation induced light in the optical fibre under MV x-ray irradiation match that of Cherenkov radiation. Different angular dependence and spectrum results from that of previous studies on radiation induced light in optical fibres have also been found. The result of the theoretical model agrees with the angle-dependence measurements.     

Flow-through immunomagnetic separation system for waterborne pathogen isolation and detection: Application to Giardia and Cryptosporidium cell isolation

Simultaneous sample washing and concentration of two waterborne pathogen samples were demonstrated using a rotational magnetic system under continuous flow conditions. The rotation of periodically arranged small permanent magnets close to a fluidic channel carrying magnetic particle suspension allows the trapping and release of particles along the fluidic channel in a periodic manner. Each trapping and release event resembles one washing cycle.The performance of the magnetic separation system (MSS) was evaluated in order to test its functionality to isolate magnetic-labelled protozoan cells from filtered, concentrated tap water, secondary effluent water, and purified water. Experimental protocols described in US Environmental Protection Agency method 1623 which rely on the use of a magnetic particle concentrator, were applied to test and compare our continuous flow cell separation system to the standard magnetic bead-based isolation instruments. The recovery efficiencies for Giardia cysts using the magnetic tube holder and our magnetic separation system were 90.5% and 90.1%, respectively, from a tap water matrix and about 31% and 18.5%, respectively, from a spiked secondary effluent matrix. The recovery efficiencies for Cryptosporidium cells using the magnetic tube holder and our magnetic separation system were 90% and 83.3%, respectively, from a tap water matrix and about 38% and 36%, respectively, from a spiked secondary effluent matrix. Recoveries from all matrices with the continuous flow system were typically higher in glass tubing conduits than in molded plastic conduits.     

A tube-excited X-ray fluorescence spectrometer for use in small-diameter boreholes

A portable in-situ x-ray fluorescence analytical system that uses an x-ray tube excitation source and a cooled Si(Li) spectrometer for detecting characteristic emission x rays has been developed for use in small-diameter wells and boreholes. The 15-watt, iron-anode x-ray tube operates up to 30 kV. Three wells at the Sandia National Laboratory Chemical Waste Landfill, lined with 76 thick polyethylene, were logged specifically for Cr contamination. Detection limits below 50 ppm were achieved with counting intervals of 600 seconds and with the Si(Li) detector operating at 450-eV resolution (full width at half maximum [FWHM] for the Mn K-alpha x ray).     

Biomedical applications of energy dispersive X-ray fluorescence

An X-ray fluorescence method for in vitro analysis of trace elements in biological samples is presented. The method is characterised by the use of an X-ray tube with secondary targets as a monoenergetic radiation source, and by thin specimens. The method has been applied to the analysis of blood serum samples, gunshot residue and urinary calculi.     

Standardless energy-dispersive X-ray fluorescence analysis using primary radiation monochromatized with LiF(200) crystal

Energy-dispersive X-ray fluorescence spectrometer (EDXRF) with primary radiation monochromatized by LiF(200) crystal was developed. In the constructed spectrometer, the radiation from the Ag target X-ray tube operated at 50 kV and 40 mA excites the secondary target (Cu, Se, Zr or Mo). The characteristic radiation (Cu K_α, Se K_α, Zr K_α or Mo K_α) of the target is monochromatized with LiF(200) crystal and excites elements in the analyzed sample. The X-ray spectra are collected by thermoelectrically cooled Si-PIN detector with resolution of 145 eV at 5.9 keV. The pinhole collimator placed in front of the X-ray detector allows reducing size of the analyzed area. Quantitative analysis is performed using standardless fundamental parameters (FP) method. Because sample is excited using highly monochromatized radiation, the calculations are much simpler and analysis error resulting from uncertainty of X-ray tube spectral distribution is completely eliminated. Moreover, EDXRF system allows obtaining very low background and appropriate secondary target can be selected for the best excitation of the determined elements and to avoid overlapping of the analyte peaks with characteristic radiation originating from the secondary target. The FP calculations were verified using several certified reference materials of stainless steel. The spectrometer was used for nondestructive analysis of mono- and polycrystals of selenide spinels of general formula M_xN_yCr_zSe₄ (where M, N are Cu²⁺, Zn²⁺, Cd²⁺, Mn²⁺, Ge²⁺, Ni²⁺, V³⁺, Sb³⁺, Ga³⁺). The results from EDXRF were compared with those obtained by means of the wavelength-dispersive X-ray fluorescence spectrometry (WDXRF).     

Dynamic x-ray diffraction studies of liquid-crystalline polyesters

Mesophase transitions in liquid-crystalline (LC) polyesters were studied by dynamic x-ray diffraction using a synchrotron radiation source. Powder and fiber samples were examined by continuous heating from 50°C to 270°C in a hot stage. The polymer systems consisted of two types of thermotropic polyesters with mesogenic cores composed of combinations of substituted terephthalate, oxybenzoate and hydroquinone units combined with aliphatic spacers placed in the main chain. One of these samples was a chemically homogeneous LC polyester (HTH12) while the other LC polyester possessed chemical heterogeneity (BP6). BP6 could also be processed to form fibers which showed thermal transition behavior by x-ray diffraction and no detectable melting or clearing transition by thermal measurements. LC textures were observed using polarized light microscopy. Results of the dynamic x-ray diffraction studies of these two LC polymers are described.     

The use of chemical contrast in the SEM analysis of polymer blends

A novel method for investigating the morphology of multiphase polymers is discussed. In this procedure, inherent differences in secondary and backscattered electron emission from the various components rather than topographical variations are used to produce image contrast. The combined use of various selective stains and energy-dispersive x-ray analysis to accentuate and positively identify individual phases is discussed. The effects of coating thickness and type and changes in accelerating voltage on image quality are also described.     

Energy-dispersive x-ray fluorescence spectrometry of industrial paint samples

An energy-dispersive x-ray fluorescence method for the direct, simultaneous determination of major and minor elements in coatings is described. The method relies on the back-scatter/fundamental parameter concept and provides a general solution to matrix problems. The method has been implemented and verified on spectrometers based both on tube excitation and radioisotope excitation. Results demonstrating some performance characteristics are presented. Sample inhomogeneity problems that impede quantification of low-Z elements in some types of paint are discussed.     

Extinction correction and synchrotron radiation

The primary extinction factor y_p is defined as the ratio of the integrated reflection from a coherently diffracting domain to the integrated kinematical reflection from the same domain. When y_p is larger than 0.5 it may be approximated by y_p = exp{−(αδ)2}, where α is about 0.5 andδ the average size of the coherent domain when measured in units of the extinction length A,δ = D/λ. Transfer equations are applied to symmetrical Laue diffraction, and the reflectivity per unit length, Σ(ε) is solved from the measured reflecting ratio as a function of the rocking angleε =θ− θ_B. Measurements with conventional x-ray sources are made on single crystal slabs of Be and Si using AgKΒ, MoKα₁ and CuKα radiation. The primary extinction factor y_p(ε) is solved from a point-by-point comparison of two measurements where the extinction length λ is changed by varying the polarization and/or wavelength of the x-ray beam. The results show that primary and secondary extinction are strongly correlated, and that the customary assumption of independent size and orientation distributions of crystal mosaics is unjustified. The structure factors for Be and Si show close agreement with other recent measurements and calculations. The limitations of the method are discussed in length, particularly the effects of beam divergences and incoherence of the rays in the crystal. It is concluded that under typical experimental conditions the requirements of the theory are met. Practical limitations arising from the use of characteristic wavelengths and unpolarized radiation prohibit the use of the full potential of the method. The properties of a synchrotron radiation source are compared with a conventional x-ray source, and it is demonstrated that the experimental limitations can be removed by the use of synchrotron radiation. A diffraction experiment with synchrotron radiation is outlined, as well as generalization of the method to small spherical crystals.     

土壤中砷形态分析研究进展

本文评述了近年来国内外土壤中砷形态分析的主要研究方法,包括联用分析法、分级提取法和同步辐射X-射线线吸收光谱法。联用分析法包括气相色谱联用法、毛细管电泳联用法和高效液相色谱联用法。重点介绍了目前应用范围较广的高效液相色谱-等离子体质谱(HPLC-ICP-MS)联用法和高效液相色谱-氢化物发生-原子荧光光谱(HPLC-HG-AFS)联用法。同步辐射X-射线线吸收光谱法近几年发展迅速,是最具发展潜力的形态分析方法。     

An ultra-violet radiation monitor for artificial weathering devices

A simple method of measuring the radiation output of artificial weathering devices below 320 nm, based on the use of polysulphone film, is described. Measurements of the output of carbon-arc, Xenon-arc and fluorescent tube sources are presented and compared with the level of radiation below 320 nm found outdoors.The use of polysulphone film to detect positional variations, lamp variability and filter ageing is demonstrated.     

Automated sampling with capillaries

A system is described for the analysis of serum contained in capillaries. The capillaries, filled with samples, are placed directly into a moving stream of diluent which flushes the capillaries, carrying the samples into a continuous flow or discrete system of analysis. The capillaries are inserted into holes in a plastic block which is pushed forward sequentially by a drive mechanism. As each capillary comes into line with an entrance tube and exit tube, reagent is pumped through these tubes and through the capillary. As an alternative, a dispenser is attached to the inlet tube, and as each capillary comes into position, a measured amount of liquid is dispensed through the capillary and into a container. The system is applied to continuous flow analysis of phosphate, alkaline phosphatase, uric acid, and creatinine. The construction of an efficient and reliable peristaltic pump is described for the continuous flow system.     

Monte Carlo Simulation in Electron Probe Microanalysis. Comparison of Different Simulation Algorithms

Practical aspects of Monte Carlo simulation of EPMA experiments are considered. Simulations are performed using the general-purpose Monte Carlo code system Penelope, which is briefly described. This code includes geometry tools and variance reduction methods that allow the practical simulation of x-ray spectra from samples with complex geometries in moderate computing times. The reliability of simple interaction models and approximations, which have been frequently used in EPMA studies, is analyzed by studying their effects on the simulated x-ray spectra.     

ESCA applied to polymers. XXII. An investigation of sample charging phenomena for polymeric films on gold

Sample charging phenomena arising in the ESCA experiment have been investigated for gold and polymer films of known thickness ranging from 5 Å to 20 μ deposited on gold either insulated from or in electrical contact with the spectrometer. Charging induced by a monochromatic x-ray source is typically an order of magnitude greater than that induced by a nonmonochromatized source and exhibits a marked time dependence. A novel source of secondary electrons which employs a low-power, low-pressure mercury lamp external to the spectrometer source chamber as an alternative to an electron flood gun is described, and the charging and biasing characteristics of polymer films as a function of film thickness are discussed and demonstrated to provide an extra informational dimension for the study of polymeric materials.     

Spectroscopic evidence for radiation-induced crosslinking of poly(tetrafluoroethylene)

Direct spectroscopic evidence for radiation-induced crosslinking of poly(tetrafluoroethylene) (PTFE) is presented for all x-ray and electron dose levels above which it is possible to distinguish between deliberately introduced radiation damage and the x-ray damage inherent in obtaining an x-ray photoelectron spectrum (XPS). The C (1s) spectrum obtained after irradiation with 2 keV electrons for all doses greater than 1 μA-min/cm² consists of a four-peak spectrum identical to that previously obtained for plasma-polymerized tetrafluoroethylene and assigned to carbon atoms with variable numbers of bound F atoms (CF₃, CF₂, CF₁, and CF₀). X-ray irradiated PTFE can be fitted with the same four-peak spectrum. At or below an electron dose level of 1 μA-min/cm², the radiation damage is comparable to that produced by the x-ray dose necessary to obtain an XPS spectrum. The CF₁ and CF₀ components increase with increasing electron dose, and at high electron doses dominate the spectrum. With increasing dose the CF₃ component approaches a constant value while both the CF₂ component and the total F : C ratio decreases. These four components are those expected to result from radiation-induced crosslinking reactions of the polymer and are consistent with previous suggestions that crosslinking is the basis of radiation patterned adhesion to PTFE. © 1993 John Wiley & Sons, Inc.     

Studies of orientation and structure of crazed matter in polystyrene. II. Electron diffraction measurements

The technique of selected area electron diffraction in the transmission electron microscope is used to examine the degree of orientation of crazed matter. The theories of electron and x-ray diffraction are compared and it is shown experimentally, by comparison with published x-ray results, that it is possible to obtain electron diffraction patterns from uncrazed polystyrene that are reasonably free of both radiation damage and multiple scattering problems. Electron diffraction patterns from crazes show a considerable degree of orientation but otherwise are very similar to those from uncrazed material, showing that crazes have no structure different from that of bulk material. Diffraction patterns are also obtained from thin films drawn to draw ratios of 4.5 and 6 at 90°C. These agree well with published x-ray results from oriented polystyrene but show less anisotropy than the craze diffraction patterns.     

Development of micro X-ray fluorescence spectrometer with multi excitation sources

X-ray fluorescence analysis (XRF) is a suitable technique for elemental analysis in nondestructive measurement. Recently, small area analysis by using the XRF technique has gained popularity. The synchrotron radiation source is responsible for the increase in the popularity of micro-XRF analysis. However, most people find it difficult to gain access to the synchrotron radiation facility. In this study, a micro-XRF system is developed for use in laboratories. To enable the use of this system, it is necessary to satisfy the following two conditions: (1) the excitation source must be optional for efficient excitation of the sample and (2) the X-rays must be focused. An X-ray tube with multi excitation sources has also been developed. In this tube, there are three targets, namely Cr, W, and Pd, on the anode, and each target can be excited sequentially. A doubly curved crystal (DCC) developed using a Si(111) crystal is used as the optics for focusing the X-rays into a beam with a diameter of less than 100 μm. A system composed of the X-ray tube and DCC optics is used to perform the small particle analysis of a Si wafer. The lower limit of detection (LLD) of the sample particle is estimated as 1.6 μm in diameter.