All ETDs from UAB

Advisory Committee Chair

Elizabeth Gardner

Advisory Committee Members

Jason Linville

Mitch Rector

Document Type

Thesis

Date of Award

2011

Degree Name by School

Master of Science in Forensic Science (MSFS) College of Arts and Sciences

Abstract

Laser Induced Breakdown Spectroscopy (LIBS) can be used to quickly determine the elemental composition of gas, liquid, and solid samples with minimal sample preparation. A LIBS instrument commonly incorporates a ND:Yag Laser and a CCD or Eschelle detector. The laser pulse ablates material from a sample, producing a high temperature plasma. The plasma emits light at wavelengths that are characteristic of the elements ablated from the sample. The emission of the plasma is collected and analyzed by a detector within the LIBS system. The advantages of LIBS are that the method is relatively non-destructive, very little sample preparation is required, and the spectra can be obtained within just a few minutes. The disadvantages are that the limit of detection is presently only 4-10 ppm and that the percent composition of trace elements cannot be determined to the level of accuracy required for forensic analyses. However, as shown by this project, LIBS can be used as a quick test when the presence of specific elements are used to identify a sample, such as lead for a bullet fragment or lead (Pb) and barium (Ba) for a suspected bullet hole. In cases that involve the use of firearms, traces of lead, barium, and antimony can be detected on the victim, criminal, and other objects that have come in contact with the firearm and/-or fired projectiles. However, when the point of impact is more than six feet from the source of the gunshot, the only residue at the site of impact may be bullet wipe, iii a dark ring of lead or barrel residue wiped from a bullet as it passes through the material. This study focused on the effects that distance on the detection of gunshot residue and bullet wipe on clothing, cement block, wood, and drywall shot at distance from 1" to 12'. Peaks at 280.16, 368.49, and 405nm are characteristic of lead and at 455.4, 493.4, and 553.5 nm for barium. The techniques developed in this project have the potential to establish an area of bullet impact detection in the presence and absence of gunshot residue.

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