A variable selection procedure for X-ray diffraction phase analysis

The X-ray diffraction method has been widely used for qualitative and quantitative phase abundance analysis of crystalline materials. We propose the use of partial least squares when building the calibration model for a quantitative phase analysis based on X-ray diffraction spectra. We also propose a variable selection procedure to reduce the measurement points in terms of angles as an alternative to using the whole pattern. The proposed method is based on the variable importance in projection derived from the partial least squares and it considers some practical issues regarding the angle measurement. The method was particularly applied to the simultaneous determination of weight fractions of some iron oxides. It was found that the number of measurement points can be reduced to 30 percent of the total number of points with a small sacrifice in prediction error.     

Total reflection X-ray fluorescence analysis with monoenergetic excitation and full spectrum excitation using rotating anode X-ray tubes

A newly constructed measuring chamber for total reflection X-ray fluorescence analysis (TXRF) has been tested for several applications. Full spectrum excitation and monoenergetic excitation of the sample are compared using rotating and standing anode tubes as primary radiation source. Advantages and disadvantages of using a W-C multilayer structure as monochromator in TXRF are discussed. Extrapolated detection limits of 170 fg (1 fg = 10⁻¹⁵ g) for Mn were obtained using a Cu-anode and full spectrum excitation.     

α-Fe/Nd2Fe14B复合纳米晶合金的X射线定量相分析

采用联立方程组确立了α-Fe/Nd2Fe14B复合纳米晶合金中相含量的计算方法.该方法运用最小二乘回归法和抛弃平均法消除病态方程组.将其应用于α-Fe/Nd2Fe14B复合纳米晶合金的相含量计算,所得结果与直接对比法一致.     

A Monte Carlo program for quantitative electron-induced X-ray analysis of individual particles

A versatile Monte Carlo program for quantitative particle analysis in electron probe X-ray microanalysis is presented. The program includes routines for simulating electron-solid interactions in microparticles lying on a flat surface and calculating the generated X-ray signal. Simulation of the whole X-ray spectrum as well as phi(z) curves is possible. The most important facility of the program is the reverse Monte Carlo quantification of the chemical composition of microparticles, including low-Z elements, such as C, N, O, and F. This quantification method is based on the combination of a single scattering Monte Carlo simulation and a robust successive approximation. An iteration procedure is employed; in each iteration step, the Monte Carlo simulation program calculates characteristic X-ray intensities, and a new set of concentration values for chemical elements in the particle is determined. When the simulated X-ray intensities converge to the measured ones, the input values of elemental concentrations used for the simulation are determined as chemical compositions of the particle. This quantification procedure was evaluated by investigating various types of standard particles, and good accuracy of the methodology was demonstrated. A methodology for heterogeneity assessment of single particles is also described.     

Ratio of slopes method for quantitative X-ray diffraction analysis

This method, which employs an internal standard, is both easy to use and accurate. The required weight fraction of a phase in the mixture to be analysed is determined from the ratio of slopes of two linear plots passing through their respective origins, designated as the analysis and reference lines. The analysis line is obtained by plotting the intensity ratio of the required phase to the standard against the weight ratio of the mixture to the standard, for different proportions of mixture and standard. The reference line for the required phase is obtained by plotting the intensity ratio against the weight ratio of the reference material to the standard, using a pure phase or a reference material of known composition. The ease of use comes when weighing out the samples to be X-rayed. The weight of the mixture to be analysed, the reference material and the internal standard need not be any specific values or in any fixed proportions but, of course, require to be determined precisely. The weight ratios can be chosen so that peak intensities can be measured accurately. Precise weighing and the ability to use various weight ratios can give this method greater accuracy than that of the conventional internal standard method.     

Characteristic X-ray excitation in thin films by 4–50 keV electron bombardment

X-ray excitation by electron bombardment has been used to analyse thin films, the main objective being non-destructive thickness determination. In a specially designed, but otherwise conventional, electron probe the thin film targets were irradiated with 4–50 keV electrons. Al, Mg, Cu and Zn films evaporated and/or sputtered onto aluminium and copper substrates were measured and the influence of the excitation energy on the sensitivity was studied in the thickness range from 20 to 5000 Å. Typical sigmoid-shaped calibration curves are found, provided X-ray excitation by the primary electrons is the dominating process. Good agreement can then be expected with calculations based on the depth distribution of characteristic X-ray generation. This is not true, however, of film-substrate systems in which X-ray excitation by electrons backscattered from the substrate becomes comparable with direct excitation (e.g. Al on Cu). Artificial enhancement of the ionization density by thin surface layers is demonstrated and applications of this effect are discussed with particular reference to energy-dispersive measurements.     

Elastic peak electron spectroscopy for quantitative elemental analysis of solids

A method based on an analysis of the spatial distribution of elastically reflected electrons is proposed for the depth-resolved, quantitative nondestructive determination of the elemental composition of solid surfaces at thicknesses in a nanometer range.     

Variation of the X-ray quantitative phase analysis method

A method to determine the composition of the phase coequilibrium with one of the components in the system under study is proposed. It is based on the use of diffraction pattern data for test samples whose representative points are located at different sides of the point of the phase in question.     

A new filter design technique for coded excitation systems

To increase range resolution and produce acceptable range sidelobe levels, filtering techniques rather than direct complex correlation are applied in coded excitation systems. A filter design technique based on both peak sidelobe levels and minimum sidelobe energy criteria is developed. In comparison to a classic inverse filter, this approach reduces sidelobe levels under a prespecified threshold. Further reduction can be achieved by extending the filter length. This technique can be more generally applied to similar signal processing problems. Both the mathematical formulation and simulation results demonstrating the utility of the technique are presented. A discussion of quantization effects is included.     

A new procedure for preparing mixed uranium-plutonium dioxide

Addition of aqueous ammonia and hydroxylamine hydrochloride to a nitric acid solution containing U(VI) and Pu(VI) causes at pH ∼7 precipitation of a mixture of U(VI) hydroxylaminate and Pu(III) hydroxide. The precipitate separated from the mother liquor and dried at 60°C upon further calcination in air at 300°C transforms into a solid solution of PuO₂ in UO₂ as a result of thermal decomposition of the precipitate with the reduction of U(VI) to U(IV) by the ligand coordinated to the uranyl ion. The developed procedure for preparing mixed U-Pu dioxide can become an alternative to the presently used method for preparing uranium dioxide and mixed uranium-plutonium oxide fuel (MOX fuel) by heating at 800–900°C in a reducing atmosphere.     

A new beamstop for microfocus X-ray capillary beams

In order to accurately measure the photon flux and to assist in aligning the beam, we have designed a modified beam stop device based on a photo diode integrated with the beam stop. The beam stop contains a small CdWO(4) crystal that completely stops the X-rays and at the same time produces photoluminescence proportional to the X-ray flux. The light is then guided to a photosensitive diode, using a flexible light pipe, to monitor the flux. With this device we achieve the goal of stopping the primary X-ray beam and simultaneously monitoring the X-ray intensity, thus eliminating the need for integrating ion-chambers into the capillary or collimator mount.     

A new high-brightness stepped-crystal diffractor for X-ray microanalysis

An electron-probe X-ray microanalyzers, the characteristic X-ray radiation is generated within a small volume of sample and the emitting surface area is on the order of 1 μm². For a distance to analyzer of approximately 0.5 m, this small emitting area can be considered as a point source. Practical implementations of the electron-probe X-ray microanalysis (EPMA) require a high spectral resolution and sufficient intensity.     

A new magnetic time-of-flight spectrometer for electron spectroscopy

A new electron spectrometer for kinetic energies below 100 eV is presented. It uses the time-of-flight technique and combines high resolution with high luminosity. A permanent magnet with soft iron pole pieces generates a rotationally symmetric magnetic field with $\text{1}\text{r}{}^2$ dependence. This field makes it possible to confine very long real flight paths within small physical dimensions. The analyzer has an overall diameter of about 0.3 m and the use of an iron magnet makes it practically insensitive to external magnetic fields. Electronic equipment for pulsing and detection is described. A transmission measurement of the 1s2s² resonance in He^? is used to test the performance of the spectrometer.