Weighting measures in fitting PIXE spectra

doi:10.1016/0168-583X(90)90235-M

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 49, Issues 1–4, 2 April 1990, Pages 161-165

https://doi.org/10.1016/0168-583X(90)90235-M Get rights and content

Abstract

An area that still requires attention in fitting PIXE spectra is the accurate determination of small peaks. This becomes important when the method is extended in an attempt to estimate small concentrations. In this paper various weighting schemes are considered, and the influence on the final peak area when fitting small peaks on a small background are discussed.

References (6)

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T. Awaya
Nucl. Instr. and Meth.
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C.G. Ryan et al.

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Cross-linking of DOPA-proteins in the eggshell of Bdelloura candida, a marine worm: A PIXE study
1996, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Mature and hatched eggshells of Bdelloura candida, a member of a family of marine worms, have been examined to determine their structure, composition and mechanism of formation. This report concentrates on the metal content with the purpose of establishing whether or not metals that can form DOPA chelates are present, and, thereby, provide a means of cross-linking. Elevated levels of Fe, Cu and Zn were observed, all of which can form such chelates.
Overlap corrected on-line PIXE imaging using the proton microprobe
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Conventional methods for PIXE imaging have used the counts recorded in a simple energy window set on an X-ray peak to approximate the image of an element. This method produces image artefacts due to the overlap of the X-ray lines of interfering elements, detector artefacts, such as peak-tails, pile-up and escape peaks, and continuum background. This paper reports on continuing development to solve this problem, based on the construction of a matrix transformation that transforms directly from PIXE spectrum vector to elemental concentration vector. This transformation provides a fast method for extracting on-line quantitative estimates of the concentration of a sample while still under the proton beam; the method has been called Dynamic Analysis to reflect this capability. If the spectrum is replaced by a single count in a channel, an event recorded at a point in a raster scan of the proton beam over a target, then the resultant concentration vector is the set of increments to make to all elemental images at that pixel. PIXE images accumulated in this way are inherently (i) quantitative (accumulated in ppm μC), (ii) overlap-resolved and background-subtracted, and (iii) can be formed directly on-line. The method is under development at the CSIRO and in routine use at the NAC using a simple procedure involving the fitting of a preliminary scan spectrum to build the transform matrix; spectrum fitting and matrix construction are part of the GeoPIXE software package. This paper outlines the method, reports various tests of it, and presents recent examples of its application to major and trace element imaging in geology.
A new method for on-line true-elemental imaging using PIXE and the proton microprobe
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A rapid matrix transform method called Dynamic Analysis (DA) has been developed for the production of true elemental images using PIXE and the Proton Microprobe that are free of image artefacts due to continuum background and overlap with X-ray lines and detector response features (e.g. tails and escape peaks) from other elements. The method has been installed at the CSIRO and the NAC for the on-line projection of true elemental images. These on-line images are also quantitative, and only require minor off-line correction (∼ 10% typically) to obtain accurate true elemental images at major and trace element levels. Correction issues discussed include the variation of PIXE yields with sample composition across a scan area, and dead-line corrections. The method is now in routine use and enables on-line quantitative true elemental imaging at the CSIRO and the NAC using a simple procedure involving the fitting of a preliminary scan spectrum to build the DA transform matrix; spectrum fitting and matrix construction are part of the GeoPIXE software package. The method has been extensively tested using samples which display complex multi-element overlaps, the DA method successfully projecting accurate images for elements obscured by the lines of interfering elements.
The nuclear microprobe as a probe of earth structure and geological processes
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The nuclear microprobe is ideally suited to the microanalysis of geological samples where trace element quantitative microanalysis and imaging are essential. The use of these methods, particularly proton-induced X-ray emission (PIXE), is becoming more common in many areas of geology as the impact of trace element data become more widely appreciated. This review provides an update on the progress of geological applications of the nuclear microprobe since these were reviewed at the previous conference on Nuclear Microprobe Technology and Applications in 1992. But more importantly, the applications described in more detail in this paper are chosen to illustrate the impact nuclear microprobe methods are having on our understanding of earth structure and geological processes, and to focus attention on the power and potential of quantitative nuclear microprobe methods for further geological research.
Enhancements in the Livermore spectrum analysis package PIXEF
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A number of enhancements have been incorporated into the Livermore particle-induced X-ray emission (PIXE) spectral fitting program PIXEF (for PIXE-Fit) in order to improve our quantitative analysis capability for data collected with Si(Li) detectors. Some of the new features include an improved description for the background which takes into account X-ray absorption effects, a better representation of the line shapes using Voigtian distributions, and a better treatment of peak fitting in regions of poor counting statistics. The implementation of these improvements into PIXEF is described.

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Weighting measures in fitting PIXE spectra

Abstract

Nucl. Instr. and Meth.

Nucl. Instr. and Meth.