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Textbook Notes for Ch 17/21/23/25.doc

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University of Toronto Mississauga
Forensic Science

FSC239 January 6 th Ch. 17 pgs 327 to 342 Microanalysis and Examination of Trace Evidence - microanalysis: the application of a microscope and microscopical techniques to the observation, collection and analysis of microscopic evidence that cannot be clearly observed or analyzed without such devices - trace analysis: qualitative or quantitative analysis of the minor or ultraminor components of a sample - sample: an entire submitted exhibit or subsample of the exhibit Instruments of Microanalysis and Sample Types - the microscope most likely to be employed first in the examination of evidence is the stereo binocular microscope o location and recovery of microscopic particles and materials from their substrates o magnification: objective lens * eyepiece o lens: an optical component that may be composed of one or multiple elements - the second most common type of microscope is the compound binocular microscope o physical dimensions by actual measurement are more useful stage micrometer micrometry: allowing evaluation of characteristics such as length, width, and thickness - light is a wave phenomenon o its characteristics are velocity, wavelength, and frequency, related to colour, amplitude, brightness, and vibration direction, which is always perpendicular to direction of travel o privileged direction: plane polarized light is obtained by the use of polymer films in which the molecules are very highly oriented and have been treated with a dye so that they almost totally absorb light vibrating in all but one direction o crossed polars: when two polarizers are placed in such a way that light passes through one and then the second and privileged directions of each are perpendicular, no light will emerge from the second o Raman spectra are generated when light from a source is scattered by the electron cloud of a molecule are complimentary to infrared spectra and supply more information concerning the backbone of the structure of the molecule whereas infrared excels at functional group identification the principle advantages that make Raman spectroscopy attractive are: 1. it is essentially a non-destructive technique 2. it requires very little, if any, sample preparation 3. laser point only illuminates the sample of interest 4. it is able to measure vibrational frequencies without difficulties in the 700-200 wavelength region there are 2 fundamental instrumental designs for Raman microspectrometers 1. disperse instrument 2. the Fourier Transform Raman Spectrometer - X-RAY diffraction: involves the targeting of a beam of monochromatic x-rays on a sample so that the radiation is scattered o displays how the atoms and molecules are arranged in a given crystal - pyrolysis gas chromatography: an organic material is broken into fragments by heating in an inert atmosphere that prevents combustion - X-RAY fluorescence, atomic absorption, atomic emission, atomic mass spectrometry Microscopic Evidence and its Analysis Glass - glass: reasonably hard, transparent or translucent material composed of fused inorganic materials o upon cooling, it is amorphous in nature on all but ultramicro or atomic scales o lacks real symmetry, is not crystalline, fractures conchoidally, and is isotropic in its optical properties o transfer evidence o radial cracks: those originating from the impact point and propagating away o concentric cracks: those that seem to make a circle around the point o when glass fractures, the edges often show characteristics referred to as conchoidal lines o physical characteristics that should be noted are: thickness, colour, uniformity, curvature, and surface conditions tinting, soiling, imperfections o float glass: manufactured by the floating molten glass onto the surface of a bath of melted tin o many techniques exist to determine whether the liquid medium or the solid sample has the higher RI oblique illumination, dispersion staining colour, and the movement of the Becke line Becke Line: a microscope is critically focussed on the sampling, and then the focus is raised the distance between the sample and the microscope objective is increased when this happens, a halo or brightness near the edge of the sample (called the Becke line) will move into the material with the greater RI single variation method the RI is determined by recording the match temperature and employing the calibrated dn/dt of the oil to calculate the RI of the sampleFSC239 th January 9 Ch. 17 pgs 350-351 Microanalysis and Examination of Trace Evidence Soils - soil: complex mixtures of materials of mineral, animal, and vegetable origin at various levels of change and decay o indication of location - pollen can be a strong indicator of a location - the soils of greater density are deemed more important than light fraction minerals Gunshot Residue - a mixture of organic and inorganic materials originating from the projectile, cartridge case, propellant, and primer that em
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