Development of confocal micro X-ray fluorescence instrument using two X-ray beams

A new confocal micro X-ray fluorescence instrument was developed. This instrument has two independent micro X-ray tubes with Mo targets. A full polycapillary X-ray lens was attached to each X-ray tube. Another half polycapillary lens was attached to a silicon drift X-ray detector (SDD). The focal spots of the three lenses were adjusted to a common position. The effects of the excitation of two X-ray beams were investigated. The instrument enabled highly sensitive three-dimensional X-ray fluorescence analysis. We confirmed that the X-ray fluorescence intensity from the sample increased by applying the two independent X-ray tubes in confocal configuration. Elemental depth profiling of black wheat was demonstrated with the result that each element in the surface coat of a wheat grain showed unique distribution.     

Development and applications of grazing exit micro X-ray fluorescence instrument using a polycapillary X-ray lens

A polycapillary X-ray lens is an effective optics to obtain a μm-size X-ray beam for micro-X-ray fluorescence spectrometry (μ-XRF). We developed a μ-XRF instrument using a polycapillary X-ray lens, which also enabled us to perform Grazing Exit μ-XRF (GE-μ-XRF). The evaluated diameter of the primary X-ray beam was 48 μm at the focal distance of the X-ray lens. Use of this instrument enabled two-dimensional mapping of the elemental distributions during growth of the plant “Quinoa”. The results of the mapping revealed elemental transition during growth. In addition, a small region of thin film was analyzed by GE-μ-XRF. We expect that GE-μ-XRF will become an effective method of estimating the film thickness of a small region.     

X-ray fluorescence imaging with polycapillary X-ray optics

X-ray fluorescence spectrometry imaging is a powerful tool to provide information about the chemical composition and elemental distribution of a specimen. X-ray fluorescence spectrometry images were conventionally obtained by using a μ-X-ray fluorescence spectrometry spectrometer, which requires scanning a sample. Faster X-ray fluorescence spectrometry imaging would be achieved by eliminating the process of sample scanning. Thus, we developed an X-ray fluorescence spectrometry imaging instrument without sample scanning by using polycapillary X-ray optics, which had energy filter characteristics caused by the energy dependence of the total reflection phenomenon. In the present paper, we show that two independent straight polycapillary X-ray optics could be used as an energy filter of X-rays for X-ray fluorescence. Only low energy X-rays were detected when the angle between the two optical axes was increased slightly. Energy-selective X-ray fluorescence spectrometry images with projection mode were taken by using an X-ray CCD camera equipped with two polycapillary optics. It was shown that Fe Kα (6.40 keV) and Cu Kα (8.04 keV) could be discriminated for Fe and Cu foils.     

X-ray spectrometry using polycapillary X-ray optics and position sensitive detector

Polycapillary X-ray optics (capillary X-ray lens) are now popular in X-ray fluorescence (XRF) analysis. Such an X-ray lens can collect X-rays emitted from an X-ray source in a large solid angle and form a very intense X-ray microbeam which is very convenient for microbeam X-ray fluorescence (MXRF) analysis giving low minimum detection limits (MDLs) in energy dispersive X-ray fluorescence (EDXRF). A new method called position sensitive X-ray spectrometry (PSXS) which combines an X-ray lens used to form an intense XRF source and a position sensitive detector (PSD) used for wavelength dispersive spectrometry (WDS) measurement was developed recently in the X-ray Optics Laboratory of Institute of Low Energy Nuclear Physics (ILENP) at Beijing Normal University. Such a method can give high energy and spacial resolution and high detection efficiency simultaneously. A short view of development of both the EDXRF using a capillary X-ray lens and the new PSXS is given in this paper.     

ArtTAX - a new mobile spectrometer for energy-dispersive micro X-ray fluorescence spectrometry on art and archaeological objects

A newly developed spectrometer for energy-dispersive micro X-ray fluorescence spectrometry has been designed for the demands of archaeometry. ArtTAX combines the advantages of non-destructive and sensitive multi-elemental analysis at sub-mm resolution with the possibility of working outside the laboratory. The spectrometer consists of an air-cooled, low-power molybdenum tube, new generation polycapillary X-ray optics, a silicon drift detector without the need for liquid-nitrogen cooling, a CCD camera, and three light diodes for sample positioning. The motor-driven measurement head is fixed on a x,y,z-flexible tripod support which can be assembled and dismantled within minutes. The spot size of the primary X-ray beam was determined to be 94 microm for the Cu(Kalpha) energy, the detection limits are in a range of a few tens of microg g(-1) for the medium energy-range in glass. Additional open helium purging in the excitation and detection paths enables the determination of elements down to sodium, thus avoiding vacuum conditions or a size-limiting sample chamber. A selection of qualitative and quantitative results on pigment, metal, glass, and enamel analyses are presented to show the potential of ArtTAX in the field of art and archaeology.     

Quantitative analysis of single aerosol particles using polycapillary X-ray optics

A laboratory micro X-ray fluorescence spectrometer based on polycapillary X-ray optics (PXRO) was used to carry out the quantitative X-ray fluorescence analysis of single aerosol particles with smaller size than that of focal spot of PXRO. The minimum detection limits measured with the thin-film reference standards were in the range from 13.3 to 0.7 ng cm^? 2 when the operating current and voltage were 70 mA and 35 kV, respectively. In order to reduce the effects of the inhomogeneous distributions of the X-ray intensity in the focal spot of the PXRO on the analysis results, the sensitivities were corrected by using a Gaussian function for the quantitative analysis of single aerosol particles. The accuracy of the analysis of single standard solution drops was on average 25% depending on the element and concentration. The precision of the analysis was better than 5%.     

Influence of the laser fluence in infrared matrix-assisted laser desorption/ionization with a 2.94 microm Er : YAG laser and a flat-top beam profile

The dependence of the signal intensity of analyte and matrix ions on laser fluence was investigated for infrared matrix-assisted laser desorption/ionization (IR-MALDI) mass spectrometry using a flat-top laser beam profile. The beam of an Er : YAG laser (wavelength, 2.94 microm; pulse width, 90 ns) was coupled into a sapphire fiber and the homogeneously illuminated end surface of the fiber imaged on to the sample by a telescope. Three different laser spot sizes of 175, 350 and 700 microm diameter were realized. Threshold fluences of common IR matrices were determined to range from about 1000 to a few thousand J m(-2), depending on the matrix and the size of the irradiated area. In the MALDI-typical fluence range, above the detection threshold ion signals increase strongly with fluence for all matrices, with a dependence similar to that for UV-MALDI. Despite the strongly different absorption coefficients of the tested matrices, varying by more than an order of magnitude at the excitation laser wavelength, threshold fluences for equal spot sizes were found to be comparable within a factor of two. With the additional dependence of fluence on spot size, the deposited energy per volume of matrix at threshold fluence ranged from about 1 kJ mol(-1) for succinic acid to about 100 kJ mol(-1) for glycerol.     

Energy-dispersive X-ray fluorescence spectrometer for analysis of conventional and micro-samples: Preliminary assessment

The energy-dispersive X-ray fluorescence spectrometer for analysis of conventional and micro-samples using pinhole collimators of various sizes is developed. The measurements can be performed in the air or, in order to decrease the absorption of long-wavelength radiation of low-Z elements, in helium atmosphere. The sample is excited by the air-cooled Rh target X-ray tube of ca. 100 μm nominal focal spot size and maximum power 75 W. The X-ray spectra of the samples are collected by thermoelectrically cooled Si-PIN detector. The tungsten pinhole collimators of the size holes from 50 to 2000 μm are placed between primary filter and analyzed sample to reduce size of analyzed area. The sample can be moved using the X–Y stage. The position of the sample is monitored by CCD camera and two laser pointers. The beam spot sizes for various collimators are evaluated by the thin-wire and knife-edge methods. Beside the beam spot sizes, the loss of radiation intensity and the changes of spectral distribution of the incident radiation caused by applying various collimators are also investigated. The sample-surface-down geometry in the designed spectrometer allows for a simple analysis of various samples: solutions, loose powders, solid samples of conventional size and micro-samples.     

High intensity monocapillary X-ray guide tube with 10 micrometer spatial resolution for analytical X-ray microscope

High-intensity monocapillary X-ray guide tube is studied and compared with a commercially available polycapillary tube. The newly designed monocapillary tube is capable of achieving spatial resolution of 10 μm in beam diameter. In comparison with the polycapillary tube, beam diameter of the present monocapillary tube is not enlarged and allows the sample to be measured at a working distance that is 10 times less. Thus, the monocapillary tube is the more versatile X-ray focusing optics as it provides improvements in spatial analysis of samples.     

Wavelength dispersive X-ray fluorescence imaging using a high-sensitivity imaging sensor

A new wavelength-dispersive X-ray fluorescence (WD-XRF) imaging spectrometer equipped with a high-sensitivity imaging sensor was developed in our laboratory. In this instrument, a straight polycapillary optic was applied instead of a Soller slit as well as a 2D imaging X-ray detector instead of X-ray counters, which are used in conventional WD-XRF spectrometers. Therefore, images of elemental distribution were available after a short exposure time. Ni Kα images and Cu Kα images were clearly obtained at corresponding diffraction angles for a short exposure time of 10 s. By optimizing the spectrometer, the time required for imaging is reduced, leading to XRF image movies. It is difficult to distinguish two peaks (Ti Kα (4.508 keV) and Ba Lα (4.465 keV)) due to the poor energy resolution of EDXRS. However, Ti and Ba images could be successfully observed by the WD-XRF imaging spectrometer. The energy resolution of the developed spectrometer was 25 eV at the Ti Kα peak.     

Ray-tracing simulation of parabolic compound refractive lenses

X-ray compound refractive lenses (CRL) are becoming a widespread tool for the generation of microfocus spot sizes at synchrotron beamlines. The calculation of their performance by means of ray-tracing is useful for a rapid estimation of flux, resolution and focusing properties achievable in a beamline, when other optics are present, or simply to study the lens acceptance and focusing in the presence of a particular bending magnet, wiggler or undulator X-ray source. The ray-tracing method presented in this paper has been used to calculate the efficiency of beryllium CRL's using, for the instrument layout, realistic source size and divergence, and usual optics like perfect crystal monochromators. It is shown that the intensity transmitted by the lens, the effective aperture and the gain are in good agreement with analytical formulas. Additional information provided when running the program are the precise shape of beam at the focus, and at any position along the optical axis. For instance the intensity distribution at the CRL entrance and exit planes allows a comparison between the effective and the geometrical apertures. Finally, the method provides a precise value for the lens focal distance, which depends on the CRL length.     

Analysis of painted steel by a hand-held X-ray fluorescence spectrometer

Steel with a paint layer was analyzed with a hand-held X-ray fluorescence spectrometer. When the 0.5 mm thick paint layer was composed mainly of light elements, alloying elements in steel such as Fe, Cr, Ni, W, and Mo were easily detected. 0.2% Mo in steel was detectable even if the paint contained Ti or Fe as a main element. The signal intensity of each element in steel decreased exponentially when the paint thickness increased, and the degree of decrease depended on the X-ray energy. Therefore the peak intensity for non-painted steel could be calculated from the paint thickness. The paint thickness was estimated from the intensity ratio Fe Kβ/Kα or W Lβ/Lα. When a paint of Ti (0.07–0.49 mm thick) was used, the peak intensities of the Fe Kα, Cr Kα, Ni Kα, and Mo Kα lines for non-painted steel were estimated by using the intensity ratio Fe Kβ/Kα, with errors of less than 30%. The content of each element in steel is estimated when the fluorescent X-rays are detectable by analysis of painted steel without removing the paint layer. On-site screening of painted steel can be performed on the basis of the alloy composition estimated by analysis with a hand-held XRF spectrometer.     

Possibilities of micro X-ray fluorescence spectrometry of solutions with preconcentration

Results of investigations in energy-dispersive X-ray fluorescence analysis aimed at the development of a high-sensitivity method of microanalysis of solutions are presented. A combined scheme of analysis of one drop of solution of the volume several microliters is proposed and tested. The scheme includes a new preconcentration method based on the drop evaporation in the presence of a micrograin of a hydrophilic adsorbent followed by the microanalysis of the solid phase on the portable device with a polycapillary lens with a focal spot of 10 μm designed at the Institute of Physical Optics. Analytically meaningful X-ray fluorescence spectra are obtained using DETATA (grain diameter about 100 μm) and SAC8 (50 μm) adsorbents and individual drops of model solutions containing Mn, Fe, Co, Ni, Cu, and Zn (0.2 mg/L and higher) and analytical characteristics of the proposed approach are demonstrated.     

Influence of the distance between a spectrometer and sample on the intensity of X-ray fluorescence

Expressions for calculating the extreme point coordinates of focal spots of X-ray tubes and a detector’s sensitive area are found. These coordinates are used in calculations of the sample area. The dependence of the X-ray fluorescence intensity on the distance between a spectrometer and an analyzed sample is studied experimentally. The intensities of the FeK _α spectral lines in iron-containing materials are calculated at different geometric parameters of a spectrometer. It is found that the distance between a sample and detector at which the maximum of the measured intensity is observed depends on the size and position of the detector and X-ray tube collimators, as well as on the relative position of the X-ray tube and detector. Recommendations on how to achieve the maximum intensity of X-ray fluorescence are proposed. The results of the present work can be used for the development of X-ray fluorescence analysis techniques applicable for free-flowing materials directly in technological processes.     

Hard X-ray micro-spectroscopy at Berliner Elektronenspeicherring für Synchrotronstrahlung II

The capabilities of the X-ray beamlines at Berliner Elektronenspeicherring für Synchrotronstrahlung II (BESSY II) for hard X-ray measurements with micro- and nanometer spatial resolution are reviewed. The micro-X-ray fluorescence analysis (micro-XRF), micro-extended X-ray absorption fine structure (micro-EXAFS), micro-X-ray absorption near-edge structure (micro-XANES) as well as X-ray standing wave technique (XSW), X-ray beam induced current (XBIC) in combination with micro-XRF and micro-diffraction as powerful methods for organic and inorganic sample characterization with synchrotron radiation are discussed. Mono and polycapillary optical systems were used for fine X-ray focusing down to 1 µm spot size with monochromatic and white synchrotron radiation. Polycapillary based confocal detection was applied for depth-resolved micro-XRF analysis with a volume resolution down to 3.4 · 10^− 6 mm³. Standing wave excitation in waveguides was also applied to nano-EXAFS measurements with depth resolution on the order of 1 nm. Several examples of the methods and its applications in material research, biological investigations and metal-semiconductor interfaces analysis are given.     

X-ray propagation through polycapillary optics studied through a ray tracing approach

Single and polycapillary optics has obtained in recent times increasing attention for its potential high efficiency as device for focusing high-energy photons and thermal neutrons. The actually developed and future applications depend strongly on a detailed knowledge of the optical characteristics of such devices. Nevertheless, an exhaustive theoretical treatment of the polycapillary properties is extremely complicated due both to the intrinsic complexity of the structure and of the interaction between the X-ray photon beam and the mono- and polycapillary surfaces.Using PolyCAD, a ray-tracing original package developed by our group, here we report a wide study concerning single and polycapillary optics properties. The software allows easily to simulate the optical path inside cylindrical, conical and curved mono- and polycapillary structures; their focusing properties are also presented and discussed.     

A new fundamental parameter based calibration procedure for micro X-ray fluorescence spectrometers

Fundamental parameter based quantification of X-ray fluorescence (XRF) measurement data requires an accurate knowledge of the spectrometer parameters, including the spectral distribution of the excitation radiation. In case of micro-XRF where a polycapillary optic is utilized in the excitation channel this distribution is changed due to the transmission properties of the lens. A new calibration procedure, based on fluorescence data of thin standard samples, was developed to determine the excitation spectrum, i.e., the product of the X-ray tube spectrum and the transmission of the used X-ray optic of a micro-XRF setup. The calibration result was validated by the quantitative analyses of certified multi-element reference standards and shows uncertainties in the order of 2% for main components, 10% for minor elements and 25% for trace elements. The influence of secondary order effects like Coster-Kronig transitions and cascade effects is analyzed and the accuracy of fundamental parameters in common databases is discussed.     

Development of a micro-X-ray fluorescence system based on polycapillary X-ray optics for non-destructive analysis of archaeological objects

A new micro-X-ray fluorescence (micro-XRF) system based on rotating anode X-ray generator and polycapillary X-ray optics has been set up in XOL Lab, BNU, China, in order to be used for analysis of archaeological objects. The polycapillary X-ray optics used here can focus the primary X-ray beam down to tens of micrometers in diameter that allows for non-destructive and local analysis of sub-mm samples with minor/trace level sensitivity. The analytical characteristics and potential of this micro-XRF system in archaeological research are discussed. Some described uses of this instrument include studying Chinese ancient porcelain.     

Development of a new total reflection X‐ray fluorescence instrument using polycapillary X‐ray lens

A new TXRF instrument combined with micro‐XRF analytical technique was proposed. An X‐ray micro‐beam was obtained by using a polycapillary X‐ray lens. The evaluated diameter of the X‐ray beam at the focal distance was 35 μm. In order to satisfy the total reflection condition of the present instrument, we attempted to cut the X‐ray micro‐beam above the critical angle of the total reflection with a slit. After the slit was applied, a clear critical angle could be observed. Using this proposed instrumental setup, we applied this to the analysis of a single particle on a flat Si substrate.     

On the use of polycapillary structures to improve laboratory Energy-Dispersive X-ray Diffractometry and Reflectometry

One of the major limits of the laboratory X-ray sources is represented by their low photon flux which induces many researchers to move to synchrotron beamlines. From this point of view, polycapillaries lenses represent an extraordinary tool to improve the performances of laboratory machine and, indeed, several models of polycapillary optics-based instruments, such as diffractometers, spectrometers etc., are currently available on the market. In this work, the application of polycapillary optics to a particular kind of non-commercial X-ray instruments, namely the Energy-Dispersive X-ray Diffractometers and Reflectometers, is proposed. The advantages and limits of the use of polycapillaries are discussed and the results of preliminary experiments are shown.