Geological Society of America

33 D5. Recent Advances in Geochemistry and Petrology

Sunday, 10 October 2021
1:30 PM - 5:30 PM
B111

QUANTITATIVE WDS COMPOSITIONAL MAPPING USING THE ELECTRON MICROPROBE

Paper number: 33-8
Program: Technical Sessions
Time: 3:05 PM – 3:20 PM

Authors

John Donovan Presenting Author
University of Oregon, Eugene, OR
Julien Allaz
ETH Zurich, Zurich
Julien Allaz
University of Minnesota, Minneapolis, MN
Anette von der Handt
University of British Columbia, Vancouver, BC
Gareth G.E. Seward
University of California Santa Barbara, Santa Barbara, CA
Owen Neill
University of Michigan, Ann Arbor, MI
Karsten Goemann
University of Tasmania, Hobart
Julie Chouinard
University of Oregon, Eugene, OR
Paul Carpenter
Washington University in St. Louis, St. Louis, MO

Abstract

Quantification of pixels in X-ray intensity maps requires the same level of rigor applied in traditional point analysis. Accordingly, X-ray map quantification should include pixel-level corrections for WDS detector deadtime, corrections for changes in beam current (beam drift), changes in standard intensities (standard drift), high accuracy removal of background intensities (off-peak or mean atomic number), quantitative matrix corrections, quantitative correction of spectral interferences, and, if required, time dependent intensity corrections (for beam and/or contamination sensitive materials). The purpose of quantification at the pixel level is to eliminate misinterpretation of intensity artifacts, inherent in raw X-ray intensity signals, which distort the apparent abundance of an element. Major and minor element X-ray signals can contain significant artifacts due to absorption and fluorescence effects. Trace element X-ray signals can contain significant artifacts where phases with different average atomic number produce different X-ray continuum (bremsstrahlung) intensities, or where a spectral interference, even an apparently minor one, can produce a false-positive intensity signal. The methods we propose for rigorous pixel quantification requires calibration of X-ray intensities on the instrument using standard reference materials, as we already do for point analysis, which are then used to quantify multiple X-ray maps, and thus the relative time overhead associated with such pixel by pixel quantification is small.

Carpenter, P.K., Zeigler, R.A., Jolliff, B.L., Vicenzi, E.P., Davis, J.M., and Donovan, J.J. (2009) Advances in electron-probe microanalysis and compositional mapping: Applications to lunar samples. 40th Lunar and Planetary Science Conference, The Woodlands, TX, 2531.

Donovan, J.J., Snyder, D.A., and Rivers, M.L. (1993) An improved interference correction for trace element analysis. Microbeam Analysis, 2, 23-28.

Donovan, J.J., Singer, J.W., and Armstrong, J.T. (2016) A new EPMA method for fast trace element analysis in simple matrices. American Mineralogist, 101(8), 1839-1853.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-363702

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