Gunshot Residue Aanalysis Essay Example for Free

Gunshot Residue A analysis EssayWhen a while is discharged, residues from the bullets force, the primer, cartridge case, firearm itself and the powder from the propulsive are expelled from gaps in the guns working parts (Pepper, 2005 118). These particles are cognize as gunshot residue ( electrical skin response) or firearm discharge residue (FDR) and are composed of partly burnt and un-burnt propellant powder, particles from the ammunition primer, smoke, lubri enkindlets, grease and metals from the cartridge. galvanic skin responses are mainly deposited on skin, the occur in which the weapon was fired, on clothing, the entrance wound of victim or any other local target materials present at the crime scene. The major primer elements are lead (Pb), barium (Ba) and atomic number 51 (Sb) usually all three elements are present on the hand after firing. Less frequent elements include aluminium, zinc, copper, silicon and potassium. natural and inorganic compounds are to a faul t present in galvanic skin responses. Organic compounds are found in propellant powder and primer mixtures whereas inorganic compounds derive from primer mixtures.GSR particles are formed when the pin strikes, the primer cap and mixture is ignited creating high levels of temperature and pressure deep bug out the cartridge. The increase of temperature melts the primer mixture and the three elements are give rised by vaporisation. As the primer mix ignites the propellant powder, an increase in pressure and temperature occurs and the bullet is released from the firearm barrel. The particles involved in this process form as liquid droplets which instantly solidify due to the quick increase of temperature followed by instant cooling. The discharge of firearm butt joint deposit residues on all persons present and not just the person that fired the gun, the analysis as to who fired the weapon must be made with precaution because any hand or body part that was close to the fired weapon may have residue appearing pursuant(predicate) with having fired the weapon. The cartridge case, bullet and bullet coating contain specific elements that can also be keeped such as zinc (Zn) and copper (Cu).There are three classifications of GSR particles which show on characteristic morphologies of GSR, regular spheroids, irregular particles and particles that form a layer of lead surrounding an inside core. The collection of GSR should be carried out instantly because GSR evidence can easily be destroyed just by washing your hands and once examined it is generally spherical in shape. inviolate evidential value of all three elements must be found by specialised equipment to sanction a gun had been fired by specific suspect(s). Electron microscope (EM) is a quality of microscope that uses a institutionalise of electrons to create an image of the specimen being analysed, it is capable of much(prenominal) high magnifications and is able to see much smaller objects in detail. They are large, expensive pieces of equipment, and require a lot of skill and training to fly the coop EM. All electron microscopes use electromagnetic and electrostatic lensees to control the path of electrons.The design of an electromagnetic lens is a coil of wire around the outside of a tube through which one can pass a current, creating an electromagnetic field. The electron beam passes through the centre of the coil of wire and down the column of the EM towards the sample. Electrons are very sensitive to magnetic fields and are controlled by changing the current through the lenses. There are cardinal types of EM, contagious disease Electron Microscope (TEM) and Scanning Electron Microscopy (SEM). Transmission electron microscopy involves a high voltage electron beam emitted by a cathode and formed by magnetic lenses. The electron beam that has been partially transmitted through the thin specimen carries information well-nigh the structure of the specimen.This information i s then magnified by a chain of magnetic lenses until it is recorded by hitting a fluorescent screen, photographic plate, or light sensitive sensor such as a camera. The image detected is displayed on a computer.SEM is a technique that uses a beam of electrons to produce magnified images of sample by detecting secondary electrons which are emitted from the surface due to excitation by a primary electron beam. The electron beam is scanned across the surface of the sample with detectors building up an image by mapping the detected signals.The beam that impacts with the sample produces 3-dimensional (3D) images of the surfaces at high levels of magnification. SEM can also reveal the actual surface details of the particles with known examples of GSR, the large particles of partially burnt powder and spheres of residues analysed can appear to be from contaminated materials and not just from the specimen. In SEM, backscattered electrons (BSE) form due to collisions between entranceway ele ctron and the nucleus of the target atom where electrons are being knocked off. BSE are used to detect contrast between areas with different chemical compositions where heavy metal elements appear brighter in the images formed and illumination metal elements appear darker. SEM has the ability to be coupled with push dispersive x-ray spectroscopy (EDS or EDX) to provide information about the elemental composition of the sample being analysed.To date the most no-hit technique is SEM/EDX, which concentrates on the inorganic particles of GSR. This technique not only bring home the bacons much of the elemental composition of mortal particles to be produced but to also enable images that show morphology and the characteristics of GSR (Jackson et al, 2011 317) . This is important because these two techniques allow GSR particles to be uniquely identified and the discovery of a suspect may appear to be guilty of a crime. Particles will either be identified as possibly being GSR or shown not to have fired the weapon. The advantage of victimisation this technique has the ability to analyse various(prenominal) particles of GSR typically the three elements lead, barium and antimony can be identified easily using this technique.(Jackson et al, 2011 315) The EDX technique detects x-rays emitted from the sample during bombardment by an electron beam to characterize the elemental composition of the analysis, features as small as 1 m or less can be analysed. When the sample is bombarded by the SEMs electron beam, electrons are knocked off from the atoms to the samples surface.The electrons from the ground state are filled by electrons from a higher state which creates an electron hole so that an x-ray is emitted to balance the energy difference between the two electron states. The number and energy of the x-rays emitted from a specimen can be measured by an energy dispersive spectrometer this gives information direct to the energy difference. The data can be interpreted in various forms from its composition to the x-ray spectrum. SEM/EDX cannot determine whether a person discharged a weapon on any occasion.Thedisadvantages of using this technique are that its cost effective, limited availability and a of import amount of training is required to operate the machine as its considered to be a specialised piece of equipment (Bell, 2006 447). SEM examines specific particulates under high magnification whereas EDX allows elemental analysis of samples. SEM/EDX is the preferred method of GSR analysis as it shows in current study that the use of this technique has increased from 21% to 26% (Ronald et al, 1996 195) this shows how reliable and accurate it is to use.Positive results are always produced and when providing evidence in court it is less frequently challenged by the judge. Over 72% of laboratories that analyse GSR use SEM/EDX and search more than 50% of the counterfoil this is composed of aluminium and is an electrically charged conducting tab w hich is directly placed into the SEM/EDX machine without sample pre-treatment (Ronald et al, 1996 197) to scrape the analysis.EDX extends the usefulness of SEM in that elemental analysis which can be performed within regions as small as a few cubic micrometres. All elements from the periodic table can be detected with this type of method.There are many other methods that have been applied to identify both organic and inorganic GSR analysis but it depends on which method you use. Time of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS), x-ray micro-fluorescence, people of colour/spot testing, inductively coupled plasma (ICP), neutron activation analysis (NAA), gas chromatography (GC) and atomic absorption spectrometer (AAS). TOF-SIMS was unyielding to have many advantages over SEM/EDX but because of its lack of high resolution imaging it could not telescope its level of expectation. TOF-SIMS analyses smokeless black powders because of the high vacuum conditions inside the instru ment but was reported to be unsuitable for volatile components such as nitro-glycerine (NG), which is a liquid substance made from glycerol, nitric and sulphuric acid.(Oliver et al, 2010)ReferencesBooks1. Suzanne Bell (2006). Forensic Chemistry. USA Pearson education Inc. 447. 2. Andrew R.W Jackson and Julie M. Jackson (2011). Forensic Science. 3rd ed. London Pearson Education Inc. 311-317. 3. Ian K. Pepper (2005). Crime Scene Investigation Methods and Procedures. 2nd ed. United Kingdom McGraw-Hill Company. 118. Journals4. Ronald L. Singer, 1 M.S. Dusty Davis, 2 B.S. and Max M. Houck, 3 M.A. (1996). Journal of Forensic Science. A Survey of Gunshot Residue Analysis Methods. 41 (2), 195-198. 5. Oliver Dalby, B.Sc, David Butler, MSc and Jason W. Birkett Ph.D. (2010). Analysis of Gunshot Residue and Associated Materials-A Review. Journal of Forensic Sciences. 55 (4), 924-926 930-931.Websites6. http//www.jic.ac.uk/microscopy/intro_em.html accessed Thursday 13th declination 2012 at 11. 12pm 7. http//mee-inc.com/eds.html accessed Wednesday 19th December 2012 at 3.09pm