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Mike Jercinovic - Trace Element Analysis

In-situ Trace Element Analysis in Complex, Multiphase Materials by EPMA



Mike Jercinovic
University of Massachusettes
Amherst, MA



M. L. Williams, University of Massachusettes, Amherst
E. D. Lane, University of Texas, Austin

Trace element analysis of high-Z accessory phases by electron probe microanalysis offers unique access to data unattainable by other analytical techniques, but also presents great challenges. The intimate relationships between beam conditions (voltage, current), spatial resolution, precision, and spectral complexity require the careful examination of all analytical parameters and their consequences, at a level commensurate with the sensitivity of the desired analysis. The high REE and actinide content, and resulting high Z of monazite, allows high direct analytical resolution (below 500nm at 10kV, depending on the realized beam diameter) due to limited electron range, but the high concentration of these elements will also produce significant fluorescence at a distance. The use of high accelerating potential in an effort to improve counting statistics is injudicious in most cases. Boundary fluorescence is a very significant problem in trace element analysis and in geochronologic analysis of monazite, as grains are commonly complex, with micro-domains that differ considerably in composition (especially Th/REE). In such instances, fluorescence at a distance can lead to errors of tens of ppm within 5 micrometers of a compositional boundary. For trace element analysis, effects such as background curvature and minor interferences can result in very large errors, 50% or more for curvature alone for concentrations at or below 100ppm. Strong background curvature is observed, and for REE- and actinide-bearing phases such as monazite, the wavelength regions available for background determination are very limited, requiring routine, high-precision scanning and regression modeling to determine reasonably accurate background intensities. In all cases, caution in interpretation and integration of all available information is necessary if the potential of the method is to be realized.

Alternative presentations:
Improved Analytical Resolution and Sensitivity in EPMA –
           Some Initial Results from the Ultrachron Development Project

Hans Bethe and Nanogeochronology

Mike Jercinovic is an Associate Professor in the Department of Geosciences at the University of Massachusetts, and supervises the Electron Microprobe/SEM Facility in the department. He received his PhD from the University of New Mexico (1988), where he was introduced to microprobe analysis by Klaus Keil. Research at UNM concentrated on alteration processes in natural basaltic glasses and the application of natural analogues to modeling the corrosion of nuclear waste form glass. Mike then supervised the MIT electron microprobe facility for several years, and worked in the private sector in electron microscopy (microelectronic evaluation) before moving on to UMass in 1997. Research at UMass has primarily involved microanalysis applied to tectonic studies, and also includes other diverse geochemical, mineralogical and materials applications. Most recently, Mike’s research focus has largely related to development of new techniques in electron microprobe trace element analysis. This research primarily applies to the analysis of high-Z accessory phases (monazite, xenotime, thorite, etc.) for geochronology, but is also finding relevance in paleoclimate research, and various petrologic applications. This research has led to collaborative development of the new Cameca SX-Ultrachron electron microprobe. This project has included significant new hardware and software dedicated to improving spatial resolution and count precision in electron probe microanalysis.

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