J.A. Maxwell

The Guelph PIXE software package III: Alternative proton database

Abstract A second X-ray production database is introduced into GUPIX to complement the existing theoretical (ECPSSR–DHS) database and to provide some estimate of analytical uncertainty due to this aspect of GUPIX; it is based on published compilations and analyses of large numbers of measured K and L subshell X-ray production cross-sections. The two databases are compared through analysis of single-element standards and standard reference materials. Good agreement is observed for the case of K X-rays. In contrast, neither the theoretical nor the “reference” database appears to be entirely satisfactory in the case of L X-rays. New work is required on L subshell X-ray production cross-sections using protons. The tools in GUPIX for film thickness determination are expanded, and tested using the two alternative databases.

An intercomparison of spectral data processing techniques in PIXE

Abstract Least-squares fitting codes developed independently at five different laboratories are used to analyse PIXE spectra of a set of biological, environmental and geological specimens. A detailed comparison of the resulting five sets of X-ray intensity data reveals a remarkably good agreement among the five techniques, despite major differences in their methodologies. This conclusion strengthens PIXEs claim to have reached maturity as a trace element analysis technique.

Quantitative PIXE microanalysis of thick specimens

Abstract Methods of standardization in quantitative micro-PIXE analysis are reviewed and various issues that bear on analytical accuracy are explored; pertinent recent work on Si(Li) X-ray detector response is included and some geochemical examples are drawn upon. Extension of the GUPIX software to deal with multilayer targets, including secondary fluorescence within and between layers, is reported; analytical examples include alloy foils and multilayer solar cell structures.

Analytic fitting of monoenergetic peaks from Si(Li) X-ray spectrometers

Abstract Monoenergetic X-ray lines produced by diffraction from a curved crystal monochromator have been used to test the applicability of the Hypermet function for Si(Li) detectors. Excellent fits are achieved; the functions parameters vary smoothly with energy, and the intensity of the non-Gaussian peak components correlates with the thickness of the frontal dead layer where charge collection is incomplete. Accurate silicon escape peak intensities are presented and the contribution to the lineshape from Compton-scattered events is discussed qualitatively.

Si(Li) Detector Lineshapes: Contributions from Atomic Physics and Detector Properties

The detailed response of an Si(Li) detector to the manganese K x-rays from a 55 Fe source was studied by least-squares fitting various spectrum models using a generalized variant of the GUPIX code. The peak-to-background ratio (>10 6 ) observed for the manganese Kα x-rays is superior in the detector used here to that observed in a crystal spectrometer, and very large spectrum intensities are recorded. In addition to well recognized effects such as the intrinsic Lorentzian distribution of an x-ray line and the approximately Gaussian detector response function, the Kα and Kβ peak shapes are influenced by multiplet structure. The Kβ shape is affected by 3p3d exchange coupling, and both Kα and Kβ are influenced by 3d spectator vacancy satellites. The flat shelf-like features below the peaks appear to be associated with escape of Auger and photoelectrons, and show a step-like structure that has not hitherto been discussed. Using an accurate energy calibration provided by simultaneously recorded rubidium K x-rays, the escape peak energy shift was shown to have the theoretical value of 1.74 keV. The escape peak width was significantly augmented, relative to the value expected for a diagram line at 4.2 keV energy, by shake-off satellites and by an additional component on its low-energy side; this observation explains the widely reported escape energy values in excess of 1.75 keV. Approximate determinations were made of the shape and intensity of the KLL radiative Auger feature and of the intensity of the KMM feature.

Micro-PIXE as a complement to electron probe microanalysis in mineralogy☆

Abstract Standardization methods and limits of detection for the analogous techniques of micro-PIXE and electron-probe microanalysis (EPMA) are compared in the context of mineralogical applications, specifically in the analysis of sulfide and oxide minerals. Micro-PIXE benefits by adopting and adapting techniques from EPMA and the two techniques are often deployed in tandem to provide a full characterization spanning major, minor and trace elements. Various examples are given of work in progress.

Deviation of the Kβ /Kα intensity ratio from theory observed in proton-induced X-ray spectra in the 22⩽Z⩽32 region

Measurements of I(K beta )/I(K alpha ) for proton-induced X-rays from thin targets in the 22<or=Z<or=32 region confirm a previously suspected systematic discrepancy between experimental data and the theoretical predictions for de-excitation of a single K vacancy in a neutral atom. The present paper is the first proton work to pay specific attention to the KMM radiative Auger satellite and to use a measured resolution function in unfolding K alpha -K beta peak overlaps. A discrepancy is common to electron-, photon- and proton-induced ionisation but sufficient precision is not yet available to reveal any small differences among the three processes, which might arise from differing multiple ionisation.

MICRO-PIXE STUDIES OF SR ZONING IN ARCTIC CHARR OTOLITHS : MIGRATORY BEHAVIOUR AND STOCK DISCRIMINATION

Abstract Micro-PIXE has been used to determine the content of strontium in the growth zones of Arctic charr otoliths. A well-defined correspondence is observed between the optically observed growth zones and the strontium zoning pattern. Line-scan data indicate whether or not the fish concerned is anadromous, and they define the years in which migration to the sea has taken place; they also are sensitive to the geographic origin of the fish. These results suggest that micro-PIXE can be a useful tool in the management and conservation of the Arctic charr.

Extension of gupix to 2H, 3He and 4He excitation

Abstract The ionization and stopping power databases in gupix are extended to deal with deuterons and helium ions. The new databases are tested through analysis of standard reference materials using pure elemental targets as standards. Good accuracy is demonstrated for elements in a NIST steel reference material. Deficiencies in the L cross-section database are demonstrated through measurements on BCR standard gold films on nickel substrates.

Micro-PIXE studies of char populations in northern Canada

Abstract Micro-PIXE analysis of trace elements in otoliths has been used as the basis for several projects on char, a fish that is important for aboriginal subsistence fisheries in Arctic Canada. Life-history patterns were originally inferred from micro-PIXE line scans of Sr distribution. These were confirmed by superposition of Sr distribution patterns on optical images of otoliths of tag-recaptured fish. Char from various populations showed differentiation in otolith primordial Sr concentration; this enables us to differentiate biological stocks and, it is hoped, eventually to assign individuals from mixed-stock fisheries to their stock of origin. Zn oscillations also correlate with annular structure and provide additional temporally constrained information on fish habitat and behaviour.