Melvyn Lintern

The New Maia Detector System: Methods For High Definition Trace Element Imaging Of Natural Material

Motivated by the need for megapixel high definition trace element imaging to capture intricate detail in natural material, together with faster acquisition and improved counting statistics in elemental imaging, a large energy‐dispersive detector array called Maia has been developed by CSIRO and BNL for SXRF imaging on the XFM beamline at the Australian Synchrotron. A 96 detector prototype demonstrated the capacity of the system for real‐time deconvolution of complex spectral data using an embedded implementation of the Dynamic Analysis method and acquiring highly detailed images up to 77 M pixels spanning large areas of complex mineral sample sections.

Maia X-ray fluorescence imaging: Capturing detail in complex natural samples

Motivated by the challenge of capturing complex hierarchical chemical detail in natural material from a wide range of applications, the Maia detector array and integrated realtime processor have been developed to acquire X-ray fluorescence images using X-ray Fluorescence Microscopy (XFM). Maia has been deployed initially at the XFM beamline at the Australian Synchrotron and more recently, demonstrating improvements in energy resolution, at the P06 beamline at Petra III in Germany. Maia captures fine detail in element images beyond 100 M pixels. It combines a large solid-angle annular energy-dispersive 384 detector array, stage encoder and flux counter inputs and dedicated FPGA-based real-time event processor with embedded spectral deconvolution. This enables high definition imaging and enhanced trace element sensitivity to capture complex trace element textures and place them in a detailed spatial context. Maia hardware and software methods provide per pixel correction for dwell, beam flux variation, dead-time and pileup, as well as off-line parallel processing for enhanced throughput. Methods have been developed for real-time display of deconvoluted SXRF element images, depth mapping of rare particles and the acquisition of 3D datasets for fluorescence tomography and XANES imaging using a spectral deconvolution method that tracks beam energy variation.

The determination of gold by anodic stripping voltammetry

Abstract A method is described for the routine determination of gold as its chloride or cyanide complex by anodic stripping voltammetry at a glassy carbon electrode coupled to a microprocessor-controlled voltammeter. The preferred supporting electrolyte is 0.1 M HCl/0.32 M HNO3, with plating at −200 mV or −1200 mV (vs. Ag/AgCl). The stripping peak potentials range from 830 to 1150 mV (vs. Ag/AgCl) depending on concentration and plating time. Precision (percent relative standard deviation) is better than 5 % for a range of concentrations between 5 μg l−1 and 1000 μg l−1. The detection limit is about 5 μg l−1 for a 5-min plating period. Interferences from Cu, Hg, Ag and other electroactive species are overcome by preliminary extraction with diethyl ether.

Field analysis of heavy metals by portable digital voltammeter

Abstract Water samples and acid extractions of stream sediments, gossans, soils and crushed pisolite samples have been analyzed in the field, using a portable digital voltammeter. This instrument, which uses the polarographic technique of anodic stripping voltammetry, can analyze to a sensitivity of 1 ppb in waters and acid extractions — equivalent to approximately 1 ppm in solid samples. The technique is at present suitable for analysis of Cd, Ph, Cu, Bi (and Zn if Cu is at low concentrations); future developments could extend the instrument capabilities to include Hg, Ag, Au, As, Sb and other elements of interest to the exploration geochemist. Water samples can be analyzed directly in the analytical cell of the instrument; for rocks, soils and biological materials an acid extraction procedure must be employed, and an aliquot of the acid extract added to the 40ml of cell electrolyte. Where a partial extraction technique is employed, e.g. by using HCl and ascorbic acid, the technique clearly does not provide total elemental analyses for the solid material. However, comparison of field results with conventional analytical methods (e.g. AAS) suggests that the technique is sufficiently accurate for the use of in-field, inter-active sampling (i.e. where the results of analysis are used to influence future sampling locations and densities) to be considered in certain types of geochemical exploration programs.

Field analysis of gold by cyanide digestion and anodic stripping voltammetry

Abstract A field analytical technique which permits effective interactive sampling has been developed for the routine determination of Au in geological materials. Gold is determined by a combination of cyanide digestion and anodic stripping voltammetry, using a robust, commercially-available instrument. Interferences due to other metals or dissolved organic matter, if encountered, are removed by first extracting the Au into either di-ethyl ether or ethyl acetate, prior to analysis. The normal working range for routine determinations of the geological material in the field is from 50 ppb to the ppm range, although a lower detection limit of 5 ppb is attainable with a longer analytical time. Results from inter-laboratory comparisons show acceptable agreement and four case studies are described. Forty samples can be prepared and analysed in a working day.