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

A feasibility study was carried out into the use of particle-induced x-ray emission (PIXE) on the ion microprobe for the characterisation of gunshot residues (GSR). We compare these results with the conventional technique, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS). Samples of gunshot residue from four different sources were collected. Individual particles of GSR were analysed by SEM-EDS using a 30-keV electron beam focussed to ~10 nm, and PIXE using a 2.5-MeV proton beam focussed to ~4 μm. PIXE revealed trace or minor elements undetectable by SEM-EDS, thereby strengthening the discrimination between different types of GSR.