Rapid quantitative mineral and phase analysis using automated scanning electron microscopy (QemSCAN); potential applications in forensic geoscience
Duncan Pirrie, Alan R. Butcher, Matthew R. Power, Paul Gottlieb, Gavin L. Miller, 2004. "Rapid quantitative mineral and phase analysis using automated scanning electron microscopy (QemSCAN); potential applications in forensic geoscience", Forensic Geoscience: Principles, Techniques and Applications, K. Pye, D. J. Croft
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QemSCAN is a scanning electron microscope (SEM) system, initially designed to support the mining industry by providing rapid automated quantitative mineral analyses. The system is based upon Carl Zeiss SEMs fitted with up to four light-element energy dispersive X-ray spectrometers. Representative subsamples are mounted into either resin or wax blocks and polished prior to analysis, or can be mounted onto carbon tape. During analysis, X-ray spectra are collected at a user-defined pixel spacing and are acquired very rapidly (c. 10 ms per pixel). The measured spectra are automatically compared against a database of known spectra and a mineral or phase name is assigned to each measurement point by the QemSCAN computer software programs. In this way the near-surface qualitative elemental composition of each particle is systematically mapped, assigned to a mineral name or chemical compound/species, and digital pixel maps of each particle are created. Depending upon a range of parameters, including the particle size and the user-defined pixel spacing (which can vary between 0.20 μm and 25 μm), approximately 1000 particles, each 1–10 μm in size, can be measured per hour using a 1 μm pixel spacing. In addition to providing a qualitative elemental analysis and mineralogical or phase assignment for each particle, data relating to particle size, shape and calculated specific density are also generated. In this study, the potential application of this automated SEM system in forensic geoscience was evaluated by the analysis of: (1) a series of soil samples, and (2) a series of dust samples from an industrial complex. In both case studies, the mine-ralogy/phase composition of each sample analysed was found to be distinctive. In addition, textural data for the soil samples and particle shape data for the dust samples show that they can be clearly distinguished. Automated SEM using QemSCAN has clear potential application in the analysis of soil or other trace evidence in forensic case work.
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Forensic Geoscience: Principles, Techniques and Applications
Forensic geoscience is an increasingly important sub-discipline within geoscience and forensic science. Although minerals, soils, dusts and rock fragments have been used as only begun to be recognized in the last ten years or so. The police and other investigative bodies are keen to encourage such developments in the fight against crime, particularly since many criminals show a high level of forensic awareness with regard to evidence such as fingerprints, blood and other body fluids. The papers in this volume illustrate some of the main principles, techniques and applications in current forensic geoscience, covering research and casework in the UK and internationally. The techniques described range from macro-scale field geophysical investigations to micro-scale laboratory studies of the chemical and textural properties of individual particles. In addition to forensic applications, many of these techniques have broad utility in geological, geomorphological, soil science and archaeological research.