H. Nullens

A computer analysis of X-ray fluorescence spectra

Abstract A method is presented for the non-linear least-squares analysis of low-energy X-ray spectra obtained by tube-excited X-ray fluorescence analysis. The method is based on a description of the full energy peaks as Gaussian distributions and the background as a polynomial. System constraints are used to keep peak position and resolution consistent with predetermined calibration expressions. The least-squares routine is based on the Marquardt algorithm but parameters are confined within predetermined physically significant intervals. The method is implemented in the computer program AXIL written in Fortra IV for a PDP 11/45 system. Tests are described which prove that the program is able to provide reliable values for the parameters.

A method for the accurate description of the full-energy peaks in non-linear least-squares analysis of x-ray spectra☆

Abstract Accurate fitting of X-ray spectra obtained with Si(Li) detectors is accomplished by a model consisting of a Gauss function and numerical corrections. The procedure is incorporated into a non-linear least-squares fitting program used for the analysis of X-ray induced X-ray fluorescence spectra.

New possibilities for least-squares fitting of mössbauer spectra

Abstract A non-linear least-squares program for the analysis of Mossbauer spectra is presented. The program is capable of resolving very complex spectra and can be used on a minicomputer system, with regard to both calculation time and memory requirements. The commonly used x 2 -minimization algorithm was slightly adapted, so as to broaden its working range. All possibilities for fixing or changing parameters are provided. Two new parameter limitation techniques, which greatly reduce the need for manual intervention during the fitting process, are discussed extensively.

Automated particle analysis of populations of silver halide microcrystals by electron probe microanalysis under cryogenic conditions

An automated particle analysis routine is implemented on an electron microprobe for analyzing the chemical composition and projective area of populations of individual silver halide microcrystals. An LN2 cryostage is used to prevent material degradation due to reaction with the impinging electron beam. The background in the EDX spectra is lowered by depositing the microcrystals on a carbon-coated copper grid, mounted in a transmission holder. The ILα/AgLα net X-ray intensity ratio, obtained from a spectrum-fitting algorithm, is used to determine the crystal composition by means of a standard-based calibration curve. The uncertainty on the concentration measurement of individual microcrystals is calculated using the uncertainties on the net X-ray counts and the uncertainties on the calibration curve. The area measurement is optimized by introducing a gray value histogram correction on each individual measurement. Overlapping microcrystals are scrapped from the analysis by defining a maximum shape factor, against which the shape factor of the microcrystal is tested. To minimize problems with drift of the cryostage, spectrum acquisition is carried out immediately after a single microcrystal has been located, based on the backscattered electron image. Several applications are discussed.

Automated energy-dispersive X-ray fluorescence analysis of environmental samples

ZusammenfassungEin Verfahren zur automatischen Routinebestimmung von 20 Elementen in Umweltmaterial wird beschrieben. Bis zu 50 Proben je Tag können verarbeitet werden. Ein energie-dispersives Röntgenspektrometer wird zur simultanen Erfassung aller Elemente bei einer Messung von 5–20 min benutzt. Die nachfolgende Auswertung der Spektren wird mittels Computer durchgeführt. Das Verfahren findet Anwendung auf Schwebestaub oder in Wasser suspendierte Substanzen, die auf Filterpapier gesammelt wurden sowie auf gelöste Elementspuren, die auf Filterpapier getrocknet oder durch Ionenaustauschpapier angereichert wurden.SummaryA procedure is described for the routine automatic analysis of 20 elements in small environmental samples. Up to 50 samples a day can be processed. The instrument uses an energy dispersive X-ray spectrometer for the simultaneous detection of all elements during a 5–20 min measurement. Computer techniques are used for the subsequent data reduction of the X-ray spectra. The technique is applicable to air particulate matter filtered from the air, to suspended material in water which is filtered on a filter paper and to dissolved trace elements which are evaporated on filter paper or are collected on a thin ion-exchange loaded paper.

Analysis of layered AlxGa1 − xAs on gallium arsenide by electron microprobe and secondary-ion mass spectrometry

Abstract Two samples containing AlxGa1 − xAs layers (several micrometers thick) of different composition deposited on a gallium arsenide substrate were analyzed by two techniques. Electron microprobe analysis was used on a cross-section of the samples to measure layer thickness, to obtain qualitative information by means ov x-ray line scans, and to determine the composition of the layers accurately by energy-dispersive x-ray spectrometry. Depty profiles obtained by secondary-ion mass spectrometry were used to study depth resolution at large depth ranges. Results obtained by the two techniques are in excellent agreement and compare favourably with other published results concerning the same type of sample.