Trace element profiling of gunshot residues by PIXE and SEM‐EDS: a feasibility study

Abstract

We critically compare particle induced X-ray emission (PIXE) on the ion microprobe with scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) for the characterisation of gunshot residues (GSR). Samples of gunshot residue from several different firearms were collected. Individual particles of GSR were analysed by SEM-EDS using a 30keV electron beam focussed to ~10nm and PIXE using a 2.5MeV proton beam focussed to ~4 microns. PIXE revealed trace or minor elements undetectable by SEM-EDS, and could discriminate GSR indistinguishable by SEM-EDS. Introduction In order to demonstrate that a suspect in a criminal investigation has fired a weapon, police authorities routinely take swabs from the clothing, skin and hair of the suspect and use electron microscopy to search for gunshot residue (GSR) particles on the swabs. These particles are condensation products of the high temperature, high pressure reactions that occur when a firearm is fired and are known to be deposited at the crime scene and on the shooter [1]. The particles are made up of material from the primer, bullet, bullet jacket, cartridge casing and the gun barrel, are spherical, and are of the order of a few microns in diameter. There are several types of particle that are characteristic of gunshot residue, including those containing Pb, Ba and Sb [2].

Composition variations in Cu2ZnSnSe4 thin films analyzed by X-ray diffraction, energy dispersive X-ray spectroscopy, particle induced X-ray emission, photoluminescence, and Raman spectroscopy

“…The measured concentrations are quite different between EDS and PIXE. EDS consistently underestimates the Sn concentration, which is similar to previous comparison of EDS and PIXE for other kinds of materials [15]. The discrepancy for other elements does not show any clear tendency.…”

“…Furthermore, the proton beam can be focused so that local composition in micro-meter scale can be probed. Therefore, the PIXE technique gives more accurate results with high sensitivity and spatial resolution and has been used in various elemental analysis applications [14,15]. In this work, we compared PIXE measurements with EDS results from CZTSe samples and found that the PIXE results are more consistent with photoluminescence (PL) and Raman spectroscopy measurements.…”

“…However, these techniques are not sensitive enough to determine the composition at the μg·g −1 level [14]. Protoninduced X-ray emission (PIXE), on the other hand, uses a proton beam of mega-electron-volt energy which generates many orders of magnitude less bremsstrahlung radiation than kilo-electron-volt electron beam used in EDS, giving PIXE an analytical sensitivity several orders better than that of EDS [15]. Furthermore, the proton beam can be focused so that local composition in micro-meter scale can be probed.…”

Ambient mass spectrometry: advances and applications in forensics

“…PIXIE has been shown to be effective for trace element profiling of gunshot residues. [6] Fourier Transform Infra-red (FTIR) and Raman spectroscopy are often combined with microscopy to provide techniques for establishing the composition of small fragments or particles. A summary of these techniques is shown in Fig.…”

“Total IBA” – Where are we?

“…SEM-EDS therefore cannot discriminate many modern primers, limiting its usefulness for forensic evidence. We have already shown that IBA can give very sensitive quantitative information on many types of primer ( [61] [62]) thereby giving IBA increased discrimination power over SEM-EDS.…”