Modelling the phenomenon of elements separation in GSR particles containing aluminum using information theory analysis and molecular dynamics simulation

Abstract

In the field of forensic science, detecting gunshot residue (GSR) particles on an individual or his belongings can connect him to a firearm discharge. One of the most important aspects in research into primer discharge residue analysis is the mechanism of residue particle formation. Understanding the particle formation mechanism should help the forensic scientist to differentiate GSR from particles originating from other sources. The elemental composition of GSR particles depends upon the type of ammunition used. Modern Western ammunition all contain a very similar priming composition, the basic elements found being Lead (Pb), Barium (Ba) and Antimony (Sb). However, some manufacturers add Aluminum (Al) to the primer mixture, this addition may result in GSR particles composition of PbBaSbAl. Our experience in analyzing GSR particles derived from ammunition containing Al suggests that the addition of Al to the primer often causes elements separation forming particles with regions of distinct composition instead of one homogenous particle type. One particle-region-type predominantly includes the elements Pb and Sb, with a small amount of Ba, and the other particle-region-type predominantly contains Al and Ba. We replicated and explained this phenomenon using information theory analysis as well as running a molecular dynamic simulation, both on large-scale systems.