Total reflection x‐ray fluorescence spectrometer with parallel primary beam

A new type of x‐ray optical device with two curved mirrors was tested experimentally for total reflection x‐ray fluorescence (TXRF). When focusing optics are used to increase the primary beam intensity at the sample position of TXRF spectrometers, it is always associated with an increase in the angular divergence, which is tolerable to only a limited extent. The possibility of improving the divergence by means of an additional curved mirror was reported in the past. One may hope that this additional mirror will correct some of the adverse characteristics of conventional x‐ray sources, such as the angular divergence and the intensity at the sample position. Copyright © 2005 John Wiley & Sons, Ltd.     

Portable x‐ray fluorescence spectrometer with a pyroelectric x‐ray generator

A portable x‐ray fluorescence spectrometer was assembled with an x‐ray generator that was driven by a 9 V dry electric battery. Several possible optimum geometries of the x‐ray generator and detector were evaluated, and the results showed that the intensity of fluorescent x‐rays was strong enough when the angle between the x‐ray generator and detector was as small as 30°. The geometrically optimized x‐ray spectrometer was applied to the analysis of paints, plastics and aluminum foils. Pigments in paint and toxic elements in plastic could be easily detected with on‐site analysis. Fe in aluminum foil was quantitatively determined down to the sub‐% level. The detection limit of Fe was 180 ppm for 100 s of measurement. Copyright © 2005 John Wiley & Sons, Ltd.     

X‐ray fluorescence analysis with a pyroelectric x‐ray generator

Several types of handy x‐ray fluorescence spectrometers are presented. The results obtained with a Niton spectrometer are presented as a goal to develop a laboratory‐made spectrometer using an Amptek Cool‐X pyroelectric x‐ray generator. A small and cheap charge‐up x‐ray emitting device and its spectrum are also presented. Handy x‐ray spectrometers are now progressing rapidly and the detection limits are in the range of a few ppm for certain elements. Copyright © 2005 John Wiley & Sons, Ltd.     

Calculation of attenuation and x‐ray fluorescence intensities for non‐parallel x‐ray beams

With the nowadays widespreaded use of x‐ray optics in x‐ray fluorescence analysis, large convergence or divergence angles can occur. This experimental situation violates a basic assumption of the usual fundamental parameter quantification procedure. In order to take beam divergences in micro x‐ray fluorescence analysis into account, a way of calculating fluorescence intensities numerically by Monte Carlo integration is described. For three examples of typical micro‐XRF set‐ups the fluorescence intensities and their deviation from the parallel beam geometry are calculated. Furthermore, we propose a new approach with ‘equivalent angles’ which correct for the beam divergences in fundamental parameter methods. Copyright © 2003 John Wiley & Sons, Ltd.     

The capabilities of an electrically cooled energy‐dispersive x‐ray detector for quantitative x‐ray fluorescence analysis

The capabilities of the Si PIN diode x‐ray detector were determined and compared with those of a standard Si(Li) detector. The x‐ray fluorescence (XRF) analysis systems assembled with these two detectors included annular radioisotope excitation sources of Cd‐109 and Fe‐55. The systems were calibrated for sensitivity and quantification was performed with fundamental parameters software. Based on the analysis of the standard reference material NIST 2710 (Montana soil), the elemental sensitivities and the limits of detection of both systems were obtained. The elemental sensitivities of the Si PIN detector for fluorescence x‐rays in the energy range up to 10 keV were comparable to those of the Si(Li) detector. At higher fluorescence x‐ray energies the sensitivity of the Si PIN detector gradually decreased and was smaller by a factor of ～4 at 20 keV. The reason was mainly the small thickness of the sensitive volume of the Si PIN diode (0.2 mm) and therefore the smaller relative efficiency of this detector. The assessed limits of detection (LODs) were comparable for the two detectors, which was mainly due to the lower spectral background of the Si PIN detector in excitation with the Cd‐109 source as a result of its smaller sensitive thickness. The accuracy of elemental determinations for the two detectors was comparable and within the limits of the assessed uncertainties, which were calculated considering all the steps of the analysis, i.e. spectrum measurement and analysis, sensitivity calibration and quantification. Copyright © 2004 John Wiley & Sons, Ltd.     

Model estimated uncertainties in the calibration of a total reflection x‐ray fluorescence spectrometer using single‐element standards

Total reflection x‐ray fluorescence (TXRF) was used for the analysis of single‐element standards, Ca, Cr, Zn, Ga, Se, Rb, Sr and Y, at various concentrations. A triplicate analysis was carried out to determine the homogeneity of the samples and the reproducibility of the results. The average estimated uncertainty (model calculated) values was compared with the predicted uncertainties (systematic or equipment related). The estimated and the predicted uncertainties showed considerable agreement except at very low concentrations resulting from excessive dilution. The discrepancies decreased as the concentrations of the analytes increased. This work indicates a very reliable dependence on the systematic or predicted uncertainties from TXRF spectrometric analysis, especially at high concentrations. Copyright © 2006 John Wiley & Sons, Ltd.     

Semiconductor Peltier‐cooled detectors for x‐ray fluorescence analysis

We discuss recent results obtained in the development of Si(Li), Si p–i–n, CdTe p–i–n and CdZnTe x‐ray detectors with Peltier coolers for fabrication of laboratory and portable XRF analyzers. The characteristics of Si(Li) Peltier‐cooled detectors are close to those of detectors cooled with the liquid nitrogen and remain the most preferred type of detectors for the tasks of x‐ray fluorescence analysis. Considerable success was obtained in the improvement of the characteristics of CdTe p–i–n detectors and CdZnTe detectors with a metal–semiconductor–metal structure, effective in the energy range up to 100 keV. The spectra of all detectors are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Application of selected fundamental parameters in x‐ray fluorescence analysis

The effectiveness of selected fundamental parameters in x‐ray fluorescence analysis previously proposed by the authors was examined with a few examples. Some synthetic fused binary disks were prepared and measured to obtain the measured binary coefficients. The theoretical influence coefficients were also calculated based on the synthetic specimens and measuring conditions using those selected fundamental parameters and compared with the measured values. It was found that the theoretical influence coefficients calculated with selected fundamental parameters agreed better with measured values than those calculated with original parameters. The synthetic fused disks, some Au–Ag–Cu alloys and some Chinese rock reference materials were measured and quantitatively calculated with the program NRLXRF, that uses original parameters, and with NRL301, that uses selected fundamental parameters, using only one calibration standard for fused disks and only pure elements for alloys. The relative errors of the results from NRL301 are much smaller than those from NRLXRF. Data for the example of pressed powders of cement published in an NBS Technical Note were also calculated with NRL301 with one calibration standard. The results are comparable to those from NBSGSC obtained with seven calibration standards. Copyright © 2003 John Wiley & Sons, Ltd.     

Development of a K‐shell x‐ray fluorescence measurement of cadmium in bone

Cadmium is known to accumulate in the human body and chronic exposures have been clearly linked to adverse health effects, showing the kidney as the critical target organ. However, there is evidence of an association between extensive environmental exposure to cadmium and alterations in bone/calcium metabolism. Therefore, it is desirable to be able to measure bone cadmium non‐invasively in humans. Tibia was selected as a measurement site and source‐excited K‐shell x‐ray fluorescence was investigated both experimentally and computationally. Initially the 88 keV γ‐rays from ¹⁰⁹Cd were used to assess minimum detectable level (MDL) of cadmium in phantoms comprising plaster of Paris (bone) and wax (soft tissue). An MDL of 3–4µg g^?1 was achieved for overlying tissue thicknesses of up to 5 mm. Alternative sources were ¹²⁵I and ²⁴¹Am. Monte Carlo simulation showed that the spectral contrast for ¹²⁵I would be poor. The 60 keV γ‐rays from ²⁴¹Am were more promising, provided that the 26 keV γ‐rays were filtered out. Experiments with ²⁴¹Am confirmed that a lower MDL could be achieved. However, the product of MDL and square root of dose (a figure of merit) was not improved. Since effective doses for these source‐excited x‐ray fluorescence procedures are low (typically of the order of 0.1 µSv or less), it may be that lower MDL would be preferred over lower dose. Nevertheless, development continues as a further reduction in MDL is highly desirable. Copyright © 2005 John Wiley & Sons, Ltd.     

X‐ray absorption and x‐ray fluorescence for the characterization of titanium oxide‐modified HPLC silicas

Titanium oxide grafted on to the surfaces of chromatographic silica was investigated by x‐ray fluorescence (XRF) and x‐ray absorption (XAS) spectroscopy and the latter used before and after the extensive use of this material as a support for reversed‐phase high‐performance liquid chromatography (RP‐HPLC). XRF indicated the formation of a complete 2:1 monolayer whereas XAS suggested the presence of more than one titanium oxide structure. These structures show some slight modification after immobilization of PMOS and use in HPLC. Copyright © 2005 John Wiley & Sons, Ltd.     

Chemical effects on x‐ray fluorescence yield of Ag+ compounds

X‐ray fluorescence measurements were carried out for silver metal and a number of silver compounds containing Ag⁺ ions such as Ag₂CO₃, Ag₂SO₄, AgNO₃, AgCl, AgBr and AgI using 59.6 keV γ‐rays, emitted from ²⁴¹Am, as the excitation source, to evaluate the value of Kβ/Kα x‐ray intensity ratio. For silver metal the value of this parameter is found to be 0.206 ± 0.003 and wide variations, 0.190 ≤ Kβ/Kα≤ 0.207, were observed for these compounds. The results are explained in terms of the charge transfer occurring between Ag⁺ and the coordinating anions. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance of polycapillary x‐ray lens for x‐ray sources with various spot sizes

The performance of a polycapillary x‐ray lens (PCXRL) is related to the spot size of the x‐ray source. The transmission efficiency of the PCXRL decreases generally with the increase of the x‐ray source spot size. Both the output focal spot size of a focusing PCXRL and the divergence of a parallel PCXRL increase with increasing source spot size. A large source spot size results in more ‘escape halo’, which affects the measured transmission efficiency and the measured output focal spot size. Copyright © 2007 John Wiley & Sons, Ltd.     

Short soft x‐ray sources

In this work we report on the characterization of pulsed soft x‐rays emitted from laser‐produced plasma. The plasma was generated by a pulsed KrF excimer laser focused on pure Si, Cu and Ta targets by 40, 80 and 120 mJ laser energies. The utilized detector was a very sensitive Faraday cup which opportunely biased was able to record time‐resolved signals of x‐rays and to estimate their energy. The found x‐rays energy values were compared with the ion temperature of the plasma obtained by fitting the time‐resolved ion current signals with a shifted Maxwell‐Boltzmann velocity distribution. The results showed that the laser‐produced Ta plasma induced bunches of x‐rays having in average the highest energy values and it was also characterized by ion temperature higher than the ones of the laser‐produced Si and Cu plasmas. Copyright © 2009 John Wiley & Sons, Ltd.     

Empirical coefficients models for x‐ray fluorescence analysis of intermediate‐thickness samples

Empirical coefficients models for correction of matrix effects in intermediate‐thickness samples are presented. Two proposed mathematical models correct simultaneously matrix effects and various masses per unit area of the samples. In the first model, it is necessary to know the masses per unit area of the samples and in the second model masses are predicted from the scattered radiation. To calculate coefficients of the models, a series of multi‐element intermediate‐thickness standards with various compositions and various masses per unit area are required. The models were tested experimentally using synthetic samples pressed into pellets and geological certificate reference materials collected on a membrane filter. The calculated concentrations were in good agreement with the certificate values. Copyright © 2004 John Wiley & Sons, Ltd.     

Determinations of low atomic number elements in real uranium oxide samples using vacuum chamber total reflection x‐ray fluorescence

Conditions for the total reflection x‐ray fluorescence (TXRF) analysis of real uranium samples for low atomic number elements using vacuum chamber TXRF spectrometer were optimized. It was observed that for analysis of low atomic number elements, almost complete removal of uranium matrix is required. Two certified reference materials of uranium containing trace elements in different concentrations were dissolved in minimum amount of high purity nitric acid. The uranium matrix from these solutions was separated by solvent extraction using tri‐n‐butyl phosphate as extracting reagent. Low atomic number elements in TXRF spectrum of the aqueous phase could be seen only after six tri‐n‐butyl phosphate equilibrations in extraction. The TXRF determinations of the certified low atomic number elements Mg and Al were made in these aqueous solutions after addition of Sc as an internal standard. The TXRF determined values for Mg were in good agreement with the certified values, whereas TXRF determined Al values differed from the certified values appreciably, probably due to the interference of Al Kα peak with escape peak of U Mα and the neighboring Si Kα peak. Copyright © 2013 John Wiley & Sons, Ltd.     

Selective excitation and integral counting of x‐ray fluorescence (SEICXRF)

This paper proposes a spectrometric method for x‐ray fluorescence, based on selective excitation and integral counting of the emitted photons by the sample. It is named SEICXRF (Selective Excitation and Integral Counting of X‐Ray Fluorescence). The general characteristics of the method are shown: the spectrometer, the spectrum acquisition, the effects involved in the determination of the jump intensity and their respective algorithms (the primary and secondary intensities and other unexpected effects), its capacity to identify elements, its sensitivity, its limitations and scope. Copyright © 2003 John Wiley & Sons, Ltd.     

Quantitative thickness determination using x‐ray fluorescence: application to multiple layers

The fundamental parameter method using x‐ray fluorescence was applied to the quantitative determination of single and multiple layer thicknesses using a compact experimental setup. Focused white‐beam radiation was obtained from a high‐voltage Mo x‐ray tube and the fluorescence spectra were acquired using a Peltier‐cooled Si solid‐state detector. The results show that in the case of single layers the accuracy of the thicknesses obtained is very good whereas for multiple layer structures the agreement is poorer, especially for the thinnest layers. This indicates a possible drawback of the standard‐free thickness determination scheme based on fundamental parameters for complex samples. Copyright © 2004 John Wiley & Sons, Ltd.