A method is described to perform automated mapping of RDX particles in C-4 fingerprints. The method employs polarized light microscopy and image analysis to map the entire fingerprint and the distribution of RDX particles. The approach is relatively quick and produces a characterized fingerprint that can be used to test sampling efficiencies of explosive trace detectors (ETDs). This method can be used to evaluate a large number of fingerprints to aid in the development of threat libraries that can be used to determine performance requirements of ETDs. A series of 50 C-4 fingerprints were characterized in this manner, and the results show that the transfer of material by fingerprints is quite variable. The number of particles varies significantly from print to print, and within a print. The particle size distributions and the particle thicknesses can be used to estimate the mass of RDX in the fingerprint. These estimates of mass were found to be within ±26 % relative of the results obtained from [GC/µ-ECD] for 4 of 6 prints, which is quite encouraging for a particle counting approach. By evaluating the average mass and frequency of particles with respect to size for this series of fingerprints, we conclude that particles 10µm to 20µm in diameter could be targeted to improve detection of traces of C-4 explosives. There are a sufficient number of particles in these size bins throughout the series to enable collection, and the mass represented by these size bins is sufficient for detection.
Journal of Forensic Sciences
C-4 explosive, contamination, explosive trace detectors, fingerprints, forensic sciences, microscopy, trace particles