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Abstract Pye, K. and Croft, D.J. (2007). Forensic analysis of soil and sediment traces by scanning electron microscopy and energy-dispersive X-ray analysis: An experimental investigation. Forensic Science International 165, 52-63. This paper reports the results of a series of experiments carried out to determine the precision of precision of soil trace comparisons based on elemental peak height ratios determined by energy-dispersive X-ray analysis (EDXRA) in a variable pressure scanning electron microscope (VP-SEM). Experiments were conducted on 'bulk' soil aggregates, ground powders prepared from the <150 µm soil fractions and on smears of both the bulk soil and <150 µm material placed onto cotton cloth. X-ray count data were obtained using area scans and spot analyses at different magnifications. The effects on elemental peak height ratios of varying the SEM chamber pressure, beam spot size, emission current and accelerating voltage was also examined. The peak height ratios for oxygen silicon, aluminium, potassium, calcium and iron were found to show little variation as a function of chamber pressure, spot size and emission current over the range examined, but a strong dependency on accelerating voltage was observed. Within-sample variation in results, expressed by the percentage coefficient of variation, was found to be lowest for area scan analyses of the ground < 150 µm fractions and greatest for the spot analyses of the bulk soil aggregates and the <150 µm fractions. We conclude that comparison of elemental peak height rations determined by EDXRA can be a useful tool for rapid screening of soil samples, especially when combined with investigation of attributes of the soil traces such as colour, fabric and the composition, shapes and surface textures of individual particles or aggregates within the soil traces. If sufficient material is available and can be readily separated without contamination or loss, higher resolution and more precise elemental data should be obtained by methods such as inductively coupled plasma atomic-emission spectrometry (ICP-AES) or mass-spectrometry (ICP-MS). Contact us to obtain a PDF version of this paper (0.5 MB). |
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