Low-power X-ray Tube Research Articles

Recent and future developments in low power total reflection X-ray fluorescence spectroscopy

Today, energy-dispersive X-ray fluorescence (EDXRF) spectroscopy with low power X-ray tubes and thermoelectrically cooled detectors provide analytical performance which in the past was restricted to systems with kW power X-ray tubes and liquid nitrogen cooled Si(Li) detectors. Especially for low power TXRF spectrometers, the sensitivity could be improved by an order of one magnitude in the last 5 years. This progress was mainly based on improvements in quantum efficiency of all components and less on high power excitation sources. Recent developments caused further improvements in the analytical sensitivity as well as in the analytical performance. The introduction of a micro-focus X-ray tube increased the excitation power by a factor of 1.3. An additional improvement could be achieved by optimizing the detector window design. By optimizing the detector entrance geometry, the solid detection angle of a silicon drift detector (SDD) was increased by a factor of 1.8. In addition, the recent development of a new generation of silicon drift detectors increased the active detector area by a factor of three enhancing the peak to background ratio by a factor of two. Furthermore, the high-energy efficiency of this new detector type was significantly improved. As a result of all these improvements the detection limit for nickel could be decreased to a value of 1 pg.

A portable semi-micro-X-ray fluorescence spectrometer for archaeometrical studies

A portable semi-micro-X-ray fluorescence (μ-XRF) spectrometer was developed in the Laboratory for Material Analysis of the N.C.S.R “Demokritos”. It utilizes a novel end-window, battery-operated, low-power X-ray tube (40 kV, 40 μA) with Au as anode material, a peltier cooled Si-PIN X-ray detector and associated electronics. The unique design of the probe-like X-ray tube anode allows very close coupling of any optical component to the tube anode, as well as to the sample position. A 240 μm pin-hole collimator was used to form the semi-microbeam. Monte Carlo calculations, as well as several sets of measurements, were performed, in order to determine the optimum geometrical and operational parameters. Preliminary results about the performance of our spectrometer are presented and compared to those reported in the literature for other micro-XRF instruments utilizing various optical elements (pin-holes, poly-capillary lenses) for focusing X-rays. The potential of this semi-micro-XRF spectrometer in the archaeometrical research is also discussed.

Analysis of Limoges painted enamels from the 16th to 19th centuries by using a portable micro x‐ray fluorescence spectrometer

AbstractMaterial analysis of Limoges painted enamels was undertaken by using an x‐ray fluorescence spectrometer equipped with a low‐power x‐ray tube, polycapillary x‐ray optics and a silicon drift chamber detector. The spectrometer, which includes helium purging for detecting elements down to sodium, can easily be assembled and dismantled within 1 h. A quantification method for enamel and glass objects was developed and verified using standard materials. The layer arrangement and possible influence on the XRF measurements were especially considered in theoretical calculations. Over 160 painted enamels from the late Renaissance and Revival periods in the 19th century in various collections were investigated. Comparison of the quantitative results from objects which are securely dated and attributed by art historians allowed a more reliable attribution of pieces with doubted authenticity. Copyright © 2004 John Wiley & Sons, Ltd.

Total reflection X-ray fluorescence spectrometers for multielement analysis: status of equipment

Multielement analysis by total reflection X-ray fluorescence spectrometry has evolved during two decades. At present commercial equipment is available for chemical analysis of all types of biological and mineral samples. The electronic industry has also benefited from scientific and technological developments in this field due to new instrumentation to determine contamination on the surface of silicon wafers (the equipment will not be covered in this paper). The basic components of the spectrometers can be summarized as follows: (a) excitation source; (b) geometric arrangement (optics) for collimation and monochromatization of the primary radiation; (c) X-ray detector; and (d) software for operation of the instrument, data acquisition and spectral deconvolution to determine the concentrations of the elements (quantitative analysis). As an optional feature one manufacturer offers a conventional 45° geometry for direct excitation. Personal communications of the author and commercial brochures available have allowed us to list the components used in TXRF for multielement analysis. Excitation source: high-power sealed X-ray tubes, output from 1300 to 3000 W, different mixed alloy anodes Mo/W are used but molybdenum, tungsten and copper are common; single anode metal ceramic low power X-ray tubes, output up to 40 W. Excitation systems can be customized according to the requirements of the laboratory. Detector: silicon–lithium drifted semiconductor detector liquid nitrogen cooled; or silicon solid state thermoelectrically cooled detector (silicon drift detector SDD and silicon-PIN diode detector). Optics: multilayer monochromator of silicon–tungsten, nickel–carbon or double multilayer monochromator. Electronics: spectroscopy amplifier, analog to digital converter adapted to a PC compatible computer with software in a Windows environment for the whole operation of the spectrometer and for qualitative/quantitative analysis of samples are standard features in the production of this instrument. The detection limits reported in the literature are presented; pricing, analytical capability, ease of operation, calibration and optical alignment as well as technical support are also discussed.

Analysis of cement using low-resolution energy-dispersive x-ray fluorescence and partial least-squares regression

A bench-top energy-dispersive x-ray fluorescence instrument equipped with a low-power x-ray tube and a gas-filled proportional counter was used to determine CaO, SiO2, SO3, Al2O3 and Fe2O3 in cement. Spectrum evaluation and quantitative analysis were performed using partial least-squares (PLS) regression. A mean relative error of 5% or better was achieved for all constituents determined. It is demonstrated how the PLS method uses both explicit (characteristic peaks of the analyte of interest) and non-explicit information (correlation between concentrations of different species) to build the regression model. It is also shown how PLS is able to combine data originating from spectra that are recorded under different measurement conditions. Copyright © 2000 John Wiley & Sons, Ltd.

Thermoelectrically cooled semiconductor detectors for non-destructive analysis of works of art by means of energy dispersive X-ray fluorescence

Thermoelectrically cooled semiconductor detectors, such as Si-PIN, Si-drift, Cd 1−x Zn x Te and HgI 2, coupled to miniaturized low-power X-ray tubes, are well suited in portable systems for energy-dispersive X-ray fluorescence (EDXRF), analysis of archaeological samples. The Si-PIN detector is characterized by a thickness of about 300 μm, an area of about 2×3 mm 2, an energy resolution of about 200–250 eV at 5.9 keV and an entrance window of 25–75 μm. The Si-drift detector has approximately the same area and thickness, but an energy resolution of 155 eV at 5.9 keV. The efficiency of these detectors is around 100% from 4 to 10 keV, and then decreases versus energy, reaching ∼9% at 30 keV. Coupled to a miniaturized 10 kV, 0.1 mA, Ca-anode or to a miniaturized 30 kV, 0.1 mA, W-anode X-ray tubes, portable systems can be constructed, which are able to analyse K-lines of elements up to about silver, and L-lines of heavy elements. The Cd 1− x Zn x Te detector has an area of 4 mm 2 and a thickness of 3 mm. It has an energy resolution of about 300 eV at 5.9 keV, and an efficiency of 100% over the whole range of X-rays. Finally the HgI 2 detector has an efficiency of about 100% in the whole range of X-rays, and an energy resolution of about 200 eV at 5.9 keV. Coupled to a small 50–60 kV, 1 mA, W-anode X-ray tube, portable systems can be constructed, for the analysis of practically all elements. These systems were applied to analysis in the field of archaeometry and in all applications for which portable systems are needed or at least useful (for example X-ray transmission measurements, X-ray microtomography and so on). Results of in-field use of these detectors and a comparison among these room temperature detectors in relation to concrete applications are presented. More specifically, concerning EDXRF analysis, ancient gold samples were analysed in Rome, in Mexico City and in Milan, ancient bronzes in Sassari, in Bologna, in Chieti and in Naples, and sulfur (due to pollution) in an old roman fresco in the church of S. Stefano Rotondo (Rome).

A Microfocus X-ray Tube Used with Focusing Collimators

The design and performance are described of a low-power copper-target X-ray tube with an elongated focus foreshortened to a diameter between 10 and 20 µm. The tube is designed for use with a specularly reflecting ellipsoidal mirror placed between 10 and 20 mm from the source and focusing the X-rays onto the sample, which may be 600 mm distant. The design maximizes the solid angle of collection of the emitted X-rays and thus achieves a high intensity at the sample. The electron beam, of circular cross section, from the gun is focused by an axial magnetic lens and then drawn out by a quadrupole lens to form an elongated spot on the target which is viewed at a small take-off angle. The limits imposed on the maximum intensity at the specimen by aberrations in the lens and by the permissible power dissipation in the target are discussed. The observed intensity is in reasonable agreement with the calculated intensity; it is comparable with that achieved with nonfocusing X-ray optics used with conventional X-ray tubes operated at a power more than 100 times as great.

Measurement of absolute blood iodine concentration during digital subtraction ventriculography.

A system to measure the absolute iodine concentration (mg iodine/milliliter blood) in the left ventricle (LV) during digital subtraction ventriculography has been developed. The technique uses a catheter to draw blood from the LV through a detection cell. This occurs as the iodine bolus passes through the heart. The cell determines iodine concentration by measuring x-ray attenuation as the iodinated blood passes between a low-power x-ray tube and a diode detector. In vitro and in vivo testing of the system was conducted. The system response was linear (r = 0.99) with respect to iodine concentration. This response was independent of hematocrit. Dispersion of contrast medium in the catheter caused distortion of the shape of the time-concentration curve. The impulse response of the system was measured and found to be independent of hematocrit. A correction algorithm based on Wiener filter deconvolution was developed. In vitro testing using simulated time-concentration curves demonstrated that the rms error in the iodine measurement after dispersion correction did not exceed 4% over the region of the time-concentration curve extending from the peak to the point on the tail where the signal fell to 50% of its peak value. Cardiac output was measured from the time-concentration curve via the indicator-dilution method in an animal model. This cardiac output measurement (COI) agreed closely with cardiac output measured simultaneously with an aortic flow probe (CO(P)), namely, COI = 1.02 CO(P)-0.03 L/min, r = 0.95, SEE = 10%, p < 0.001.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative x-ray microfluorescence analysis of small areas and individual particles

During the past few years, rapid progress has been made in the development of collimated x-ray sources which permit energy-dispersive x-ray analysis of small areas with dimensions below 100 μm. An x-ray microfluorescence spectrometer developed at NIST employs a commercial low-power (50 WATTS) x-ray tube providing a small focused x-ray beam (0.25 × 0.25 mm). The x-ray beam size was further reduced with a Mo collimator tipped with a Pt foil having a 70μm hole in the center. The x-ray beam profile was measured by step scanning across Cu wires 50 μm in diameter in both X and Y directions. The cross section of the beam was approximated by a Gaussian function with a FWHM of 43 μm. A schematic diagram of the spectrometer which is capable of operation in vacuum is shown in Figure 1.Other features include a close coupled source-sample-detector for optimum count rate, a motorized x-y stage, and a color video camera for continuous viewing of the sample at normal incidence.

Measurement of salt surface density on polluted insulators using a simple x-ray fluorescence technique

A simple x-ray fluorescence technique using a low power x-ray tube and a neon gas-filled proportional counter following a multichannel analyzer has been developed for the nondestructive and rapid measurement of the density of salt deposited on the surface of power insulators. To detect faint Cl K x-rays accurately interfering x-rays such as K x-rays from argon in the air and from composite elements of the insulator glazing material are eliminated by using an x-ray filter of 30 μm thick polyvinylidene chloride placed in front of the counter window. The technique was applied for crevis type suspension insulators of 250 mm dia, having surfaces which were artificially deposited with NaCl of 0.01 to 0.1 mg/cm 2 surface density. The relative statistical error for a surface salt density of 0.1 mg/cm 2 was 1.1% using a 100 s measurement time. The positional distribution of deposited salt and the time variation of salt accumulation on the insulator surfaces were also observed with the technique.

X-ray fluorescence analysis of polymetallic ores

An analytical procedure for determination of Fe, Ti, V, Ni, Co and Cu, the most important constituents of the polymetallic ore has been developed. Twenty four powdered samples were prepared from the material taken in various places of the ore deposit. The samples were analyzed by wavelength dispersive (WD) and energy dispersive (ED) XRF method. The EDXRF method was applied using radioisotope source as well as a low power X-ray tube (Rh-anode) for excitation of the characteristic K-line radiation of the elements. A Si(Li) detector was used for the detection of radiation. The detection limits and precision of the analytical procedures, using reference materials, were estimated. The accuracy of the different XRF techniques is discussed. The developed analytical procedures based on the XRF method are rapid and quite simple. They can be useful for exploration data accumulation.

Autoradiography by X-ray-excited optical luminescence (XEOL): Application to scheelite and fluorite mineralisation

This paper investigates the practical application of XEOL as an autoradiography technique of use in characterising the mineralogy of geological samples. A simple apparatus is described in which thin sections are excited with a low-power X-ray tube operated at 19 kV, 0.9 mA. Luminescence is detected on photographic film (400 ASA) using a camera focused through a leaded glass window onto the rear of the thin section. XEOL autoradiographs, recorded for exposure times varying from 3 to 120 min., are presented for zinc sulphide powder (a test sample), scheelite (in a wolframite-bearing quartz vein) and fluorite plus calcite (in a fluorite-calcite-quartz vein) the latter two samples being collected from mineralised localities in the Eastern Highlands of Scotland, U.K. These XEOL autoradiographs show not only the distribution of the specified phases, but also delineate textural information of value in interpreting mineralisation processes.

Development and Application of Low Power X-Ray Tube Excitation System for Energy Dispersive XRF Analysis

The results achieved with an excitation system developed by using a low power, changeable anode X-ray tube are presented. The X-ray tube was fitted to a vertical Si(Li) spectrometer and supplied by an X-ray power supply developed for low power X-ray tubes. The X-ray yields and detection limits were investigated as a function of tube voltage and current in the range of atomic numbers Z = 13 … 58. The detection limits obtained with the X-ray tube are compared to ones achieved by using Fe-55, I-125 and Am-241 radionuclides. A new detection – excitation system was also constructed consisting of a 45° Si(Li) cryostat and a flexible measuring chamber. The details of this system are also given.

Extension of measurable range of film dosimetry by a low energy X-ray absorption method

The availability of an X-ray absorption technique employing a very low power X-ray tube was examined to extend measurable range for photographic film dosimetry. The X-ray tube having titanium target was operated at 8 kV and 0.2 microA to emit Ti KX-rays of moderate intensity. The degree of the Ti KX-ray absorption, defined as similar to photographic density, was measured for the two kinds of badge film, Fuji gamma-ray badge film and Kodak personal monitoring film, type 2 exposed for 60Co or 137Cs gamma-rays and developed by the respective standard procedures. The experimental results show that the dosimetric range of 0.01-100 R for the Fuji film and 0.03-1,000 R for the Kodak film may be easily measured by 1 minute counting with the relative statistical error (sigma) of 10%.

Characteristics of Low Power X-Ray Tubes

The results of investigations of the low power X-ray tubes with transmission anode, constructed in the Institute of Physics and Nuclear Techniques (IPNT) are presented. The X-ray spectra for copper, molybdenum and silver anodes were measured and the yield of the tube with the silver anode was compared with the yield of an 109Cdsource. The one-day and the several-days yield stabilities were checked. The conclusions and the perspectives of further studies are also given.

Development of a low power monoenergetic X-ray tube for trace element analysis

A system for trace elemental analysis by X-ray spectrometry has been developed. The system consists of a secondary fluorescence low power X-ray tube, a Si(Li) detector with associated pulse processing system and minicomputer. The spectrometer has been used for routine analysis of blood specimens.

Small X-Ray Tubes for Energy Dispersive Analysis Using Semiconductor Spectrometers

Fast X-ray fluorescence analysis with radioisotope excitation requires intense sources to produce reasonable counting rates. The inconvenience of handling such sources and the small number of suitable radioisotopes places severe limitations on their use.We have explored the possibility of using low-power X-ray tubes as exciting sources for energy-dispersive fluorescence analysis. The principal advantage to X-ray tubes is the ability to produce X-ray fluxes to three orders of magnitude higher than those obtained with convenient radioisotope sources while dissipating only a few watts in the tube. Furthermore, the variety of possible anode materials and range of currents in the tube make possible optimum choice of exciting energy and intensity for particular applications.We have designed and tested such tubes in a variety of anode configurations suitable for fluorescence excitation. Using either X-ray filtering techniques or multiple fluorescence geometries It is possible to significantly reduce the Bremsstrahlung background relative to characteristic radiation.As compared with normal radioisotope-target assemblies, excitation of a sample by the X-ray tube results in comparable sensitivity in only a tenth to one hundredth of the time.