17 forensic science powerpoint chapter 17 microanalysis of exam

1. Forensic Science An Introduction to Scientific and Investigative Techniques Stuart H. James and Jon J. Nordby Chapter 17 CRC Press: Forensic Science, James and Nordby, 3rd Edition

Microanalysis and Examination of Trace Evidence

Chapter Authors: Thomas A. Kubic and Nicholas Petraco

Presentation created by Greg Galardi,Peru, Nebraska

Edited by Stuart H. James, Fort Lauderdale, Florida and

Dan Mabel, Richmond, Virginia

Microanalysis is the application of a microscope and microscopical techniques to the observation, collection, and analysis of microevidence that can not be clearly observed or analyzed without such devices

Deals with samples in milligram or microgram size ranges

Trace evidence - qualitative or quantitative analysis of the minor or ultraminor components of a sample

Sample entire submitted exhibit or a subsample of the exhibit

Large forensic laboratories are generally more specific: fiber, hair, mineralogy, paint, serology, firearms analyses, controlled substances

Small laboratories may be grouped differently, such as in sections of chemistry, biology, microscopy, drugs and ballistics

Microscopes arethe first tool used to examinetrace evidence

Stereo binocular microscopes, compound in nature, are often used

Lens optical component that may be composed of one or several elements

Stereo microscopes have two separate eyepieces, and views are separated by a small angle (15 degrees)

Use of stereo microscopes allows for item being examined to been seen separately by each eye. This creates the appearance of three-dimensions.

Stereo microscopes are normally used with reflected light

Compound binocular microscope second most common type of microscope encountered in laboratory

Two eyepieces are present, however, both eyes see the same image

This microscope often employs transmitted, bright field illumination

Objective (OBJ)

Eyepiece (EP)

Magnification (x) amount subject is enlarged by lens system, the objective, eyepiece or other

Working Distance (WD) distance between the subject and the closest portion of the objective when focused

Depth of Field (DF) total distance, height, above and below the point of focus that appears clearly focused

Angle of Acceptance (AA) maximum angle between light waves that an OBJ can collect

Numerical Aperture (NA) - NA = N sin AA/2

Resolving Power (RP) - Ability to distinguish fine differences in structure

N -lowest refractive index (RI) material between the subject and the objective

Refractive Index (RI) Velocity of a light in a vacuum divided by the velocity of light in the medium of interest

A scale calibrated with a stage micrometer can be placed in the eyepiece of microscope to measure an items:

Length

Thickness

Chemical tests can be performed on micro or ultramicro samples under a microscope

Color and micro-crystal tests for identification of substances, or reactions to a solvent can be observed

Light is a wave phenomenon. Its characteristics include:

Velocity

Wavelength

Frequency

Amplitude

Vibration direction

Wavelength and frequency are inversely related

Can become partially or totally polarized by:

Reflection

Adsorption

Propagation through an anisotropic material

Normal light is randomly polarized, which means vibration direction of light is in all directions (360 directions)

Plane polarized light - vibration is only in one direction

Polarized Light Microscopes (PLMs) also may have an accessory slot in the intermediate accessory tube, which allows for placement of additional devices into optical path

Compound microscope fitted with certain accessories can be converted to a polarized light microscope (PLM)

Two polarizing elements:

Polarizer- placed in condenser mount prior to lens

Analyzer usually positioned in body of microscope in intermediate accessory tube

Most analytical capability is the characteristic RIs of anisotropic materials

Materials are divided into uniaxial and biaxial classes

RIs of these materials are characteristic rather than universal unless certain parameters of measurement are controlled and stated

Instrument of choice to characterize many forms of microscopic materials

Can lead to clear, unambiguous identifications and can aid significantly in individualization and association

There are other microscopes that are used, comparison microscopes and macroscopes that are used

Most common accessories for accessory slot of a PLM are compensators

Compensator- anisotropic materials of known birefringence constructed so that thickness is controlled and orientations of vibration are known

Compensators can be fixed or variable, and measure retardation in nanometers

Lowest total magnifications are found on macroscopes: seldom rise above 60 diameters

Use reflected light to examine evidence

Very useful in identification of large tool marks, fabrics, and ballistic marks (stria) on cartridges

Instruments that generate transmission, reflection, or adsorption spectra from various translucent or opaque samples

Principal types of instruments are visible and infrared

Commonly used to analyze colored fibers or paint surfaces

A microscope that permits viewing of samples at much greater magnification and resolution than is possible by light microscopes

Magnification is possible in the range of 10 to 100,000x

When combined with a energy dispersive x-ray spectrometer, (EDS) this tool becomes invaluable

SEM/EDS combination can readily resolve a particle smaller than 1 micrometer in size, while generating spectra revealing elemental size of object

SEMs are more valuable due to development of low pressure or low vacuum systems which allow sample being studied not to be kept at such great reductions in pressure

X-Ray diffraction

Pyrolysis Gas Chromatography/Mass spectrometry

X-ray fluorescence

Atomic absorption

Atomic emission

Atomic Mass Spectrometry

Glass is a common type of evidence

Commonly encountered as transfer evidence

Examination of broken glass can reveal whether the impact that caused the fracture was caused by low or high velocity blunt trauma (Coring Effect)

Radial crack those cracks originating from impact point and propagating away

Concentric crack- those cracks seeming to make a circle around the point of impact

Conchoidal lines those edge characteristics of glass fractures. They are stress marks shaped like arches that are perpendicular to one glass surface and curved nearly parallel to the opposite surface. The perpendicular surface faces the side where the crack originated

When microscopic glass chips are examined, the following properties are evaluated:

Physical thickness, uniformity, color, curvature, surface conditions-tinting, soiling, etc

Optical most significant property is Refractive Index

Elementalcomposition of glass

In order to determine whether liquid medium or solid sample has a higher refractive index, three methods are commonly used:

Oblique Illumination

Dispersion staining color

Movement of Becke line

However, better accuracy is required for advanced criminalistics work

Hairs and furs are natural fibers of animal origin

Hair examiners can often conclusively eliminate a person as a source of hair

However, rarely can the examiner absolutely associate a hair to a person

Hairs are generally grouped by racial origin and body location

Furs can generally be classified by species with a microscope

Subclassification of fur is difficult without an extensive reference collection

Basic characteristics of color, length and curliness may be valuable

Hair and Fur are composed of keratin, melanin and trace metals

Structure of hair :

Cuticle- outermost portion of hair

Cortex contains cortical fusi and ovoid bodies and is between medulla and cuticle

Medulla- center portion

Parts of hair or fur:

Proximal end - Root portion or bulb

Distal end - Tip of hair

Anagen Stage- Period of growth of hair

Catagen Stage Transition phase

Telogen Stage dormant or sloughing stage

Racial origin of hair can be determined and classified as Caucasian, Negroid or Mongoloid

Scales cover the shaft of the hair and point away from proximal end to distal end.

The scale structures are normally divided into three different types.

Types of scales are:

Petal triangular or protrude from shaft and usually found on cats, seals, minks

Imbricate flattened scales, like shingles on a roof and generally found on humans

Mosaic -resemble stacks of paper cups and found on small rodents and bats, rarely humans

Hair can be determined from any location: head, pubic area, limb, beard chest, pubic, axillary or other areas.

Trace metal comparison in hairs has met with limited success

Fibers are a common class of microscopic evidence.

They have numerous major classifications and generic subtypes, are physically different, are processed many ways, transfer easily, have significant persistence and thus are valuable forensic evidence.

Fibers may be grouped as animal, vegetable, or mineral

Also categorized as naturally occurring, manufactured, and synthetic

Use of microscopy for initial examination and collection of first analytical data is accepted forensic procedure

Fiber is analyzed under microscope and the following are documented:

Size, Crimp, Color ,Luster, Possible cross section, Damage, Soil andAdhering debris

Initial examination is followed by examination with a polarizing light

microscope

Examination of fibers is carried out under crossed polars and with plane polarized light

Fiber is determined to be isotropic or anisotropic

Almost all isotropic fibers are from glass

SEM/EDS allow determination of elemental composition of fiber

Paint samples are a major portion of microsamples submitted to laboratories

Paint samples usually involve paint transfer and vehicular accidents

Paint transfer from architectural sources- crimes against property are submitted occasionally

Paint is composed of:

Binders which hold all components together and is of a polymeric nature, consisting of natural or synthetic resins

Pigmentswhich supply paint color

Extenders are added to paint to increase its solid content and its opacity and hiding ability

Modifiers are added to paint formulations and affect paint films durability, gloss, flexibility, hardness, resistance to ultraviolet radiation, and other characteristics

Paint films can be investigated according to a number of physical and chemical characteristics

When paint is to be analyzed, it is best to submit entire object to laboratory

When this is impractical, paint must be removed from object and submitted

Collect sample from area close to thealleged contact and any other additional samples

First part of paint examination is the goal of obtaining a physical match

Fit of jigsaw edges or match of surface striae questioned is strong evidence

If physical match is not obtained, layer structure order, color, thickness, and other details should be documented

Angle cuts and thin sectioning with a scalpel also can reveal layer structure

Chemical reactions can also serve as sources of data

Fluorescence microscopy, Infrared microspectrophotometry and recently available Raman microspectrometers are all other options for analyzing paint

SEM/EDS, x-ray diffraction, x-ray fluorescence, pyrolysis with gas chromatography also may be used

PLMs are excellent tools for soil analysis

Soils are separated, then the minerals are identified by color, shape, and optical properties

Mineral content of soil assists in indicators of location of soil sample

Gunshot Residue (GSR) is a mixture of organic and inorganic materials originating from theprojectile, cartridge case, propellant, and primer that emerge from the barrel and openings of the firearms

Determination of GSR is to confirm residue is indeed GSR

Methods to analyze gunshot residue include Instrumental neutron activation analysis, graphite furnace atomic absorption, and inductively coupled atomic emission spectroscopy

Sample is considered when certain elements, normally barium and antimony, are found together above a baseline level

SEM/EDS can be used to analyze possible gunshot residue

Consideration in collection of gunshot residue and analysis should include possible environmental contamination, location of sample, and where sample was collected web of hand, palm, other parts of the body, etc

17 forensic science powerpoint chapter 17 microanalysis of exam

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