X-Ray Fluorescence Analysis
- Forensic Applications of X-Ray Fluorescence Microscopy (Spectroscopy Europe, June 2009)
- Forensics Applications of X-Ray Fluorescence Spectroscopy in Combination with Advanced Light Source Sample Discovery (Spectroscpy: Applications Notebook, March, 2007)
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Forensic scientists generally require fast and non-destructive analysis of a very wide range of materials. Often these materials are presented in very small quantity, as evidence collected from a crime scene. Micro-XRF offers detailed elemental analysis with a spatial resolution which can vary from the millimetre scale down to 10 µm. The elemental ‘fingerprint’ which XRF reveals is used to identify unknown materials, match crime scene materials to those found on suspects and provide vital information on explosive/gunpowder constituents. Furthermore, XRF mapping allows gun shot residue patterns to be observed, paint cross sections to be characterised, and it also provides a unique and specialised fingerprint/latent imaging technique. With these capabilities it is perhaps no surprise that the XGT-7200 is found in forensic laboratories across the world.
Since a large part of forensic analysis involves matching one material with another, the SLICE database and archiving software module is a key addition to forensic scientists’ capabilities. Developed in conjunction with the FBI, it allows the XRF spectra of materials to be archived with photographs and information on origin and composition. It is then a simple matter to search through the database according to material type and composition, or to find a spectral match to a spectrum acquired from an unknown sample. SLICE takes the analyst beyond finding out what a sample contains, and answers the ultimate question: what is it?
Key areas which benefit from micro-XRF include:
- Material identification
- Glass fragments
- Gun shot residues
- Fingerprint imaging
- Paint cross sections
- Internal structure imaging
- Inks and pigments
Gun shot residue imaging clearly illustrates the concentrated cluster of residue and bullet/barrel debris deposited when a bullet is fired through a textile. Patterning observed in such analyses can be used to understand the distance of the gun from the object
Analysis of microscopic glass fragments allows compositional differences to be identified. The optical image shows a single 120 µm particle observed using the high magnification optical microscope of the XGT-7200. Spectra from two different glasses are shown, illustrating differences in elements present at percent and sub-percent concentrations.