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gunshot residue

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by

ashley shropshire

on 17 October 2013

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Transcript of gunshot residue

gunshot residue
where is it found
GSR can be found on the hands, clothing, or any other surface that is close to a gun when the weapon is fired. The appearance of the pattern will vary with distance and can be used in distance determination studies. Samples can be taken from the hands of someone who is suspected to have recently fired a gun, and these samples can be tested for the presence of . A negative result does not mean that a gun was not fired since the time that the residue will remain depends on many factors, including the frequency and thoroughness of any hand washing. Typically, residue will persist for a few hours unless the hands are washed.
how is it tested and about it
Many of the older chemical tests for GSR targeted nitrite and nitrate ions. These include the Griess test the and the Walker test. Limitations of these tests include the lack of specificity and the widespread use of nitrates and related compounds in many products. Nitrates are found in fertilizers cigarette smoke and cosmetics to name just a few sources, so finding nitrates on a person or an object s not conclusive evidence of GSR. A variation of these tests, the dermal nitrate test used a paraffin cast of the hands that was then tested for the presence of nitrates. Due to the number of false positives encountered, this test has been largely abandoned. Another presumptive test exists for lead using sodium rhodizonate.


extra
Since GSR contains particulates, one of the most valuable tools for identifying it is the microscope. Particles that appear to be GSR can be separated and subjected to specific chemical and instrumental tests to confirm the identification. A scanning electron microscope coupled to an X-ray device (SEM/XRD) is particularly valuable since chemical analysis can be conducted on the particle as it is being observed. Samples that are to be analyzed using SEM are collected on an aluminum disk with an adhesive attached, and particles can be lifted this way from clothing or other surfaces.
what is it & where does it come from
The residue that escapes from a gun when it is fired. The most common elements found in GSR are lead , and barium, and this combination of elements. When a particle is found to contain these elements, it is almost certainly gunshot residues considered a type of transfer evidence. The residue comes mostly from the primer, which is part of the cartridge containing the bullet and propellant in modern ammunition. Particles of unburned powder are also part of the residue.
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