An exploratory study of the potential of LIBS for visualizing gunshot residue patterns

- The capabilities to perform GSR elemental analysis by LIBS has been proved.
- The GSR elemental distribution pattern has been highlighted using LIBS.
- The capability to perform a LIBS reanalysis of the sample has been demonstrated.

The study of gunshot residue (GSR) patterns can assist in the reconstruction of shooting incidences. Currently, there is a real need of methods capable of furnishing simultaneous elemental analysis with higher specificity for the GSR pattern visualization. Laser-Induced Breakdown Spectroscopy (LIBS) provides a multi-elemental analysis of the sample, requiring very small amounts of material and no sample preparation. Due to these advantages, this study aims at exploring the potential of LIBS imaging for the visualization of GSR patterns. After the spectral characterization of individual GSR particles, the distribution of Pb, Sb and Ba over clothing targets, shot from different distances, were measured in laser raster mode. In particular, an array of spots evenly spaced at 800 μm, using a stage displacement velocity of 4 mm/s and a laser frequency of 5 Hz was employed (e.g. an area of 130 × 165 mm2 was measured in less than 3 h). A LIBS set-up based on the simultaneous use of two spectrographs with iCCD cameras and a motorized stage was used. This set-up allows obtaining information from two different wavelength regions (258-289 and 446-463 nm) from the same laser induced plasma, enabling the simultaneous detection of the three characteristic elements (Pb, Sb, and Ba) of GSR particles from conventional ammunitions. The ability to visualize the 2D distribution GSR pattern by LIBS may have an important application in the forensic field, especially for the ballistics area.

123