V. N. Korolyuk

Some features of X-ray registration using a JXA-8100 electron-probe microanalyzer

Specific sources of measurement errors have been studied. In the presence of perturbing radiation, the automatic setting of the spectrometer discrimination mode is not reasonable. When choosing the transmittance window, the dependence of the shift of the amplitude distribution on the counting rate should be taken into account. Losses of intensity can be significant. The value of effective dead time is 1.3 μs for spectrometers with flow methane-argon counters and 1.2–1.5 μs for spectrometric channels with sealed xenon counters. The mode of constant dead time is retained till the intensities of 100–150 kcps. The instrumental error of routine analysis is insignificant as compared with the statistical error of count collection. In the spectra from LiF crystals, a dip in intensities is adjacent to the shortwave wing of the AuLα radiation line. Measuring intensities on it results in overestimates of the analyte concentration, and line weakening, which occurs because of the spectral hole, in contrast, leads to its underestimation. For this reason, in determining small concentrations of gold, using the Lα line as an analytical one seems unreasonable.

Accuracy in the determination of the compositions of main rockforming silicates and oxides on a JXA-8100 microanalyzer

The individual sources of errors in procedures used for considering matrix effects were studied. The ZAF and PRZ analytical programs provided good correction in the predominance of one of the matrix effects, namely, absorption or the atomic number. Their simultaneous occurrence increased the total error to 2–4 rel %. In the ZAF method, normalization to oxygen in terms of stoichiometry introduced errors if the sample simultaneously contained the test element in various oxide forms. The greatest error of up to 1–2 wt % appeared in simple and double oxides. In the analysis of the main rockforming silicates with the determination of total iron as FeO, the presence of Fe2O3 can change the concentration of components to ∼0.2%.

Synthetic TRPO4 crystals as reference samples in the quantitative X-ray electron probe microanalysis of rare-earth elements

Crystals of 15 rare-earth element phosphates, which provide a set of standard reference samples in X-ray electron probe microanalysis, were synthesized and tested for homogeneity and stoichiometry. The phosphates were synthesized in two stages, the preparation of aqueous phosphates and crystal growth in a solution of potassium polymolybdate K2Mo3O10. The tests of the synthesized crystals confirmed their reliability as reference samples.

Metrological characteristics of lead determination in rare earth phosphates by electron probe microanalysis

An equation for the calculation of the detection limit clim is presented. Relations for the limit of detection clim, limit of determination cmin, and relative error V of analyte determination are derived. The performance characteristics of lead determination in rare earth phosphates on a JXA-8100 microanalyzer are found. Under the typical conditions of the determination of monazite age (15 kV, probe current of 250 nA, count time in the positions of the line and background 400 s each) cmin using the 2σ-criterion is 0.006 wt % for an ordinary spectrometer and 0.004 wt % for a high-aperture one. In the simultaneous registration of lead by the scheme ”two ordinary plus one high-aperture channel,” cmin is reduced to 0.003%. For cmin = 0.006%, the acceptable error of age estimates V of 1–3 relative percent is attained at clim = 0.3-0.08%, respectively. As was found, the lowest capacity of microanalyzers for geochronology needs is 0.02–0.03% of PbO. Equations of constraints for the performance characteristics of methods ensure the revelation of the necessary conditions of analysis and compliance with them.

Recording lead Mα line in rare-earth phosphates using a JEOL JXA-8100 microanalyser

Conditions of recording the Pb Mα line and the background in monazite age dating are studied on an example of simple synthetic rare-earth phosphates. By selecting cutoff thresholds, pulses were discriminated from the radiation superimposing on the analytical signal in the highest orders of reflection. The interfering lines are Y Lγ2,3, Th Mζ1, and Th Mζ2. High-aperture and standard spectrometers of the microanalyser do not ensure the complete resolution of Th radiation with the Pb Mα line, and its software allows the analyst to take into account the superposition of only one element. The contribution of interfering radiation is insignificant: the presence of 1% Y2O3 or ThO2 results in the overestimation of PbO by ∼0.009 and 0.002%, respectively. The nearest free regions for measuring background are at ±4.5 mm from the Pb Mα line. Using the background measured in the short-wave region systematically underestimates the amount of PbO by 0.098 wt %. Measurements on the other side lead to overestimation by 0.061%. Calculations of the average background value are more preferable and underestimate the results by approximately 0.019%. To decrease the error more, one should record a spectrum for the determination of its bremsstrahlung component under the lead line.

Quantitative electron probe microanalysis of oxygen in compounds with pentavalent vanadium: an ultrastrong absorption phenomenon

Electron probe microanalysis of oxygen in vanadium compounds gives values which are substantially smaller then the actual oxygen content. By measuring the intensity of the O Kα line in V2O5 the absorption coefficient of V was found to be 51 000 cm2 g−1, which is much higher than the corresponding values from commonly accepted sources. To explain this phenomenon, we suggest selective absorption of the O Kα line by the strong white line of the absorption spectrum of pentavalent vanadium. Copyright