Development of a Laser-Induced Breakdown Spectrometer for Lead-Free Gunshot Residue Analysis

Gregg, Ryan Alexander (2010) Development of a Laser-Induced Breakdown Spectrometer for Lead-Free Gunshot Residue Analysis. Undergraduate thesis, under the direction of Nathan Hammer from Chemistry and Biochemistry, The University of Mississippi.

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Abstract

Research has demonstrated that Laser‐Induced Breakdown Spectroscopy (LIBS) can be used as an effective method of screening for the common elemental components in gunshot residue. Barium (Ba), lead (Pb), and antimony (Sb) make up the primer cap of most ammunition involved in forensic gunshot residue analysis. Recently, ammunition manufacturers have started producing and popularizing ammunition with zinc (Zn), titanium (Ti), and gadolinium (Gd) primer components that are non‐toxic to the environment. This paper discusses the development of the Ole Miss Department of Chemistry and Biochemistry’s first LIBS instrument for forensic analysis of lead‐free using Gd as a tracer element for identification purposes. A Silva method of sampling was adopted using a non‐emissive 3M tape to lift GSR from the subject’s hands after firing the weapon. Samples using the lead‐based and lead‐free bullets were analyzed by LIBS system consisting of an Ocean Optics USB2000 CCD Camera with a Continuum 1064 nm Nd:YAG laser as the excitation source. Each sample was analyzed by multiple laser pulses fired at various locations on the sample surface. Spectra was taken from Ba, Pb, Zn, and Gd standards and emission lines were identified for all elements but Gd. Lead‐free and lead‐based gunshot residue sample spectra were also obtained, but were found to be too noisy for emission line identification due to the lack of a time‐ controlled camera system. Further discussion in this thesis describes how this problem can be rectified so that this project may continue in the future.

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