Selective x-ray Bragg spectrometry: optimizing fluorescence microprobe sensitivity for precious metals

Autor: J. Maser, Cathy Harland, Barbara Etschmann, Joël Brugger, Daniel Legnini, Stefan Vogt, Chris Ryan
Rok vydání: 2007
Předmět:
Zdroj: X-Ray Spectrometry. 36:111-121
ISSN: 1097-4539
0049-8246
DOI: 10.1002/xrs.937
Popis: The next challenge is in rendering the instrument more user-friendly and in reducing detection limits. We present here the results from an instrument development project aimed at developing an X-ray spectrometer configuration for the X-ray fluorescence microprobe optimized for the detection of precious metals in geological and biological samples. The objective is to improve detection limits and reduce interference from major elements and beam scatter. The approach used Bragg diffraction from a surface shaped to form a segment of logarithmic spiral (log-spiral) to focus X-rays from precious metals onto a solid-state detector. The result is an enhancement of precious metal lines within the narrow band-pass of the Bragg crystal surface with suppression of detector artefacts such as tailing and escape peaks arising from interfering elements and scattered photons. BACKGROUND Gold in ore can be economic at concentrations of a few ppm, depending on ore mineralogy and the nature of gold residence in the ore. Consequently, interest in the distribution of gold between coexisting sulphide minerals in ore demands the imaging and analysis of gold at ppm to sub-ppm levels. Similarly, thermodynamic data suggest that the concentrations of gold in the fluids involved in ore formation in magmatic hydrothermal systems are seldom higher than a few ppm. Hence, the study of ore fluids trapped and preserved as fluid inclusions in minerals necessitates the detection of gold at ppm to sub-ppm levels during in situ analysis of fluid inclusions. Gold anomalies in soils and calcrete are often in the range of 10s to 100s of ppb; knowledge of gold speciation in these fine-grained samples is fundamental for understanding the origin of these anomalies and in ranking anomalies to select the most prospective exploration targets. In the biomedical sciences, platinum in the form of cis-platin plays a major role in many chemotherapeutic drugs. Mapping and quantifying platinum distributions within tissues and single cells is therefore of great interest, e.g., to study the mode of action of chemotherapy drugs on tissues and cells on a sub-cellular level, as well as how these are altered in cells that develop resistivity against a specific drug. This knowledge could then be applied to the development and testing of new chemotherapeutic agents.
Databáze: OpenAIRE
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