Ion Beam Analysis of Gunshot Residue Particles for Forensic Investigations

Gunshot residue particles are the condensation products of the high pressure, high temperature reactions that take place when a gun is fired. They are typically a few microns in diameter and the particles of interest contain the elements Pb, Ba and Sb. In order to link a suspect to a shooting incident, police swab the hands of shooters and use scanning electron microscopy to look for GSR particles. In the recent case of the murder of the TV presenter Jill Dando, Barry George was convicted of murder on the basis of gunshot residue evidence that was recently discredited. It was thought that the gunshot residue was most likely to have originated from a source of contamination – perhaps from the firearms officer who arrested Barry George or from the analysis procedures that were used. This has highlighted the need for more sophisticated methods for detecting gunshot residue from different sources. Ion beam analysis is an suite of analytical techniques that can be used to probe the chemical and elemental composition of materials. The techniques use a small particle accelerator to generate an ion beam (normally protons or helium) which is used to non-destructively probe the sample of interest. Because ion beams can be focussed to micron dimensions, it is possible to locate and probe individual particles – making the techniques ideally suited to the study of gunshot residue. We have recently found that ion beam analysis is much more sensitive to the trace element composition of gunshot residue particles than the conventional police methods. Assuming that different ammunition produces different gunshot residue, ion beam analysis should help to rule out contamination in future police case work. Working in a forensic context is an exciting but complicated environment with a great deal of validation required before a new technique can be used in court. In this project, the student will analyse gunshot residue from our collaborators from forensic institutions in the UK and in Europe who have all expressed an interest in using this technique and are helping with the validation exercise. The student will obtain training in ion beam analysis and scanning electron microscopy and will be offered the opportunity to travel to other labs within Europe to help to validate the analysis.