X-ray Capillary Optics Research Articles

Micro X-ray Fluorescence of Particles Using a Laboratory X-ray Source and Capillary Optics

Micro X-ray fluorescence (micro-XRF) is a useful nondestructive technique for multielement analysis of samples from a few hundred to a few micrometers in size. Micro-XRF is usually performed at synchrotron sources where element sensitivities are not compromised by micrometer spatial collimation of high flux beams. Ideally, micro-XRF would not have the burden of transporting samples to a synchrotron facility, but could be performed on a laboratory or portable scale. At the National Institute of Standards and Technology we are developing a micro-XRF system that combines a polycapillary optic with a standalone X-ray tube. This optic not only transmits the X-ray beam over 80 mm, but also focuses the beam to an area smaller than the unfocused beam size. The fine resolution combined with a high intensity produces a tool for laboratory scale micro-XRF analyses.The X-ray focusing optic is a tapered, glass polycapillary optic. This optic, contained in an approximately 5 × 70 mm steel cylinder, transmits and focuses incoming X-rays to a spot 9.5 mm from the optic exit.

Microscopic X-ray fluorescence analysis and related methods with laboratory and synchrotron radiation sources

The present status of microprobe versions of XRF analysis with tube excitation and with synchrotron radiation sources is reviewed with respect to analytical parameters such as lateral resolution and imaging capability, and achievable detection limits, precision and accuracy. The main characteristics of the method are contrasted with those of other microanalytical techniques. For laboratory source µ-XRF, results with a rotating anode tube equipped with capillary X-ray optics are discussed in terms of sensitivity and achievable lateral resolution. The possibilities of the new third generation synchrotron radiation storage rings, especially those of the European Synchrotron Radiation Facility (ESRF) and its X-ray micro-fluorescence, imaging and diffraction beamline (ID 22) are discussed and related to second generation storage rings. Some characteristic applications are given to illustrate the recent possibilities of the methodologies, in particular for the characterization of atmospheric particles, and in an analytical problem related to archaeology.

Highlights of x-ray spectrometry for microanalysis

A review of selected highlights of x-ray fluorescence spectrometry applied to the analysis of micro-samples and/or for localized area analysis is presented from a historical perspective. A look towards the future indicates broader commercialization of laboratory instrumentation for microanalysis and compositional mapping due to important advances in capillary x-ray optics.

Highlights of x‐ray spectrometry for microanalysis

A review of selected highlights of x-ray fluorescence spectrometry applied to the analysis of micro-samples and/or for localized area analysis is presented from a historical perspective. A look towards the future indicates broader commercialization of laboratory instrumentation for microanalysis and compositional mapping due to important advances in capillary x-ray optics. © 1997 John Wiley & Sons, Ltd.

A micro-XRF spectrometer based on a rotating anode generator and capillary optics

The analytical characteristics of a laboratory-scale micro-X-ray fluorescence spectrometer, based on a rotating anode X-ray generator and capillary optics, are described. Usually, a microbeam 15 μm in diameter, derived from a copper or molybdenum anode operated at 45 kV, is used for sample irradiation. Elemental yields around the 1 count s −1(μg cm −2) −1 level are obtained, corresponding to absolute detection limits for thin samples in the 0.05–1 pg range and to relative MDL levels of 3–10 ppm for thick organic samples. The use of the instrument for studying (trace) element migration in Roman glass and for the nondestructive analysis of decorations on Japanese 18th century porcelain vases is described.

Performance study of polycapillary optics for hard x rays

In order to investigate the feasibility of using Kumakhov capillary x-ray optics for high energy x-ray applications, measurements have been performed on the behavior of capillary optics from 10 to 80 keV. Transmission efficiencies of straight polycapillary fibers of different types have been measured as a function of source location and x-ray energy. The measurements are analyzed using a geometrical optics simulation program, which includes roughness and waviness effects. Despite the low critical angle for total external reflection at high energies, capillary x-ray optics appear promising for many hard x-ray applications. Transmission measurements at high energies have also proven to be a very sensitive tool in capillary quality analysis.

X-ray capillary optics test and applications on an undulator beamline at ESRF

X-ray capillary optics test and applications on an undulator beamline at ESRF

The use of x-ray capillary optics for lithography and microscopy

The possibilities of using x-ray capilary optics in lithography and microscopy are discussed. It has been shown experimentally that these systems, originally proposed by M. A. Kumakhov, may considerably simplify experimental designs. A micropinch x-ray source specially designed for these purposes has been successfully tested. The complete system constructed for laboratory use may serve as a prototype for an industrial lithography machine or microscope.

Imaging characteristics of x‐ray capillary optics in digital mammography

Computed radiography (CR) has shown promise in digital mammographic screening due to its good low spatial frequency MTF and its relatively wide exposure latitude. The CR image format has not gained acceptance clinically because of reduced high spatial frequency resolution as compared to film-screen images. X-ray capillary optics, aligned between the breast and CR phosphor imaging plate, will capture primary x-ray photons almost exclusively. Due to the very small angle of acceptance, scattered photons angled more than about 1.6 x 10(-3) radians from primary trajectory will not be accepted at the capillary optic entrance. The virtual elimination of detected scatter means almost 100% of the possible primary contrast should be visible in the image. In addition, the image can be magnified without focal spot blurring. Effective resolution of CR images can be increased by a factor equal to that magnification. Clinical implementation of future capillary optics are expected to be either in the form of a large, stationary, post-patient optic that accepts primary from the entire breast or a fan-shaped optic that is scanned across the breast. Measurements of a test capillary optic showed a reduction of scatter fraction to 0.018. Images of a lucite contrast detail phantom revealed a corresponding increase in image contrast when compared to anti-scatter grid and no grid methods. Spectral transmission measurements using a high-purity germanium detector showed good primary transmission (45%-50%) in the mammographic energy range. The MTF measurements of both stationary and scanned capillary optics showed improvement at the 5% MTF level to 8.4 mm-1 for scanned optics and 9.2 mm-1 for stationary optics representing a 68% and 84% respective increase over the CR MTF without magnification or capillary optics.

On the interference of X-rays in multiple reflection optics

An explanation is given for interference observed at the focal point of regular X-ray capillary lenses. X-ray capillary optics is compared with the optics of Fresnel zone plates.

Improved capillary optics applied to microbeam x-ray fluorescence: Resolution and sensitivity

A new and improved type of x-ray capillary optics unit (ellipsoidal), is developed, tested, and characterized using a table-top x-ray microbeam setup. The beam profiles of the x-ray beams generated by the 7.5 μm ellipsoidal capillary were constructed from ‘‘knife-edge’’ scans across the beam. The detection limits for various elements were determined, and the spatial resolution, when the beam was used in scanning mode, was demonstrated.

Defect analysis using a third-generation x-ray microdiffractometer with total reflection capillary x-ray optics

We have built a third generation X-Ray Micro-Diffractometer (XRMD) which is capable of examining the structure of single grains as small as 3 microns by utilizing, in part, cylindrical or conical glass capillaries as x-ray focusing optics. The idea of using capillaries as total reflection focusing optics for x-ray diffraction is not new. However, these capillaries were usually of poor quality with inner diameters nominally larger than 10 microns, and due to the general unavailability of scanning XRMDs, and high brilliancy sources, they were used primarily with back reflection cameras. Cylindrical precision bore capillaries with thick internal walls, smooth enough to be suitable for use as total reflection x-ray focusing elements, are now commercially available in long sections with inner diameters as small as 10 microns. A methodology was established to fabricate, in-house, conical capillaries with inner diameters less than 3 microns and various taper geometries. Using such focusing elements the gain in the diffracted intensity, over that achievable using a simple aperture approach, could be varied up to 4X and 30X for cylindrical and conical capillaries respectively, by varying the capillary geometry, and are discussed below.

Pulsed-plasma-based x-ray source and new x-ray optics

In this review, the problems under investigation in the I. V. Kurchatov Institute of Atomic Energy are discussed concerning x-ray generation in the range of 1–50 keV by pulsed power and new x-ray capillary optics for x-ray lithography, medical diagnostics, and science. A new x-ray tube driven by pulsed power generator (I>100 kA, V>1 MV, T<10−7 sec) has been demonstrated. Because of the strong magnetic field self-focusing in diode, enhanced Kα emission per atom of anode foil takes place. In experiments with an imploding plasma cylindrical shell (liner), a new approach to x-ray generation was investigated. Liner kinetic energy was used for plasma heating by compression to temperature at which heat transport to a small plate at the end of the liner begins to be important in the energy balance. As a result, a significant part of the liner energy can be converted to line radiation of high-Z plasma. In this way, three-dimensional compression of the energy can be realized and a 1–2 mm size x-ray source in a 1–10 keV range can be created. Together with a lens made from thousands of glass capillaries up to 6 μm inner diameter, in the near future it will be possible to have an x-ray projector with a brightness of 1025 photons/cm2 sec strd in the 20–30 keV range and with divergency of 10−3 rad for high-space resolution diagnostics in science and medicine. The new x-ray capillary optics are based on the principle of total external reflection from the inner glass tube wall. High efficiency of photo transmission along capillaries in the energy range 10–50 keV and capability to bend the capillary and photon flax by an angle of 0.1 rad has been demonstrated.

X-Ray Microbeam Spectroscopy with the Use of Capillary Optics

X-ray micro analysis had suffered from the limited intensity of conventional X-ray sources like X-ray tubes etc. However, with the optical technique described in this paper, the so called “X-ray Capillary Optics” (XCO), it is possible to make X-Ray Fluorescence (XRF) analysis in micro-scale, down to a few μm2 still with conventional sources.