[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

A number of publications have been devoted to the

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A number of publications have been devoted to the evaluation of differ- ent instrumental methods for the classification and discrimination of forensic glass fragments using chemical composition data. Reeve first reported the use of SEM/EDX as a means to further discrimination of glass samples that were not distinguishable by refractive index and density only. Studying glass samples, he compared the ratio of the concentration of each element to the concentration of calcium. He achieved very good discrimination. Ryland [705] described a classification scheme for sheet vs. container glass samples using SEM microprobe determination of Ca/Mg intensity ratios and XRF Ca/Fe concentration ratios. Total reflection X-ray fluorescence (TXRF) is a relatively new technique designed for surface analysis, which has found some application in foren- sic science. This technique uses a primary beam with a very low glancing
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724 J. Zi¸eba-Palus angle, so that X-rays mainly reflect from the surface, penetrating only the top layer (several tens of ˚ Angstroms). This reduces scattering and improves the signal-to-noise ratios. A detailed description of the TXRF technique can be found in a paper by Klockenk¨ amper et al. [700]. Kubic et al. [702] reported the application of TXRF and a related technique to the analysis of small glass fragments. The detection level was less than or equal to 10 pg for 50 el- ements, from phosphorus to uranium. Little sample preparation is needed for semiquantitative screening, while dissolved samples give results comparable to other quantitative analysis techniques. A promising X-ray technique for the analysis of small irregularly shaped glass fragments is the µ -beam XRF technique developed in Sweden and re- ported by Rindby et al. [699, 704]. This technique incorporates a very narrow beam of X-rays focused by conical capillaries. Application of capillary optics enabled the development of microbeam instruments of sensitivity comparable to instruments using conventional optics. Using this technique they detected, e.g. calcium in samples in quantities of 40 fg. They ascertained that the precision of determinations is consider- ably higher compared to SEM. Analysing the results of the classification of glass samples on the basis of determination of the elemental composition by both methods, they concluded that measurements with the XRF method have greater discrimination power and divide the examined group of glass samples into a greater number of subgroups. Kuisma-Kursula [703] has reported a study on accuracy, precision and detection limits of SEM/WDX, SEM/EDX, and proton induced X-ray emis- sion (PIXE) spectroscopy in the multielemental analysis of medieval glass. The SEM/WDX and SEM/EDX methods were suitable for analysing major and minor components of glass samples. Trace element ( < 1 wt%) analysis was possible using the WDX or PIXE method. The PIXE method proved to be the most sensitive. Hicks et al. [722] assess the potential of µ -XRF in classifi-
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