FRSC1030 Foundations of Forensic Science Chapter 19

Analyzer

One of the two polarizing elements that are positioned in the microscope’s optical path, placed specifically in the microscope’s body.

Anisotropic substance

A substance that has a physical property that has a different value when measured in different directions, such as calcite, which has a different crystal structure depending on the perspective, and for which light entering from different directions and angles will encounter different atomic environments.

Backscattered electrons (BSEs)

High-energy electrons from the primary beam in a scanning electron microscope (SEM) that are reflected back out of a sample through elastic scattering, used to create images with compositional contrast where areas with higher atomic numbers (heavier elements) appear brighter than areas with lower atomic numbers.

Becke line method

A technique used in microscopy to determine the relative refractive index of a transparent particle compared to its surrounding medium, which involves observing a bright line (Becke line) at the particle’s edge and noting its movement as the microscope’s focus is changed.

Birefringence

Also called double refraction, the optical property of a material to split a single ray of light into two rays that travel at different speeds and follow different paths, because the material’s refractive index depends on the polarization and direction of light, occuring in anisotropic materials.

Concentric cracks

Fractures that form a circular or semi-circular pattern around a point of impact that appear after the initial radial cracks.

Conchoidal lines

Smooth, curved, shell-like fractures that appear on brittle materials like glass and some rocks when they break, created by a sharp impact and can indicate the direction of force.

Delusterants

Substances that reduce the shine of some fibers, and may exhibit other surface treatments such as for repelling water, antimicrobial properties, and providing sun protection.

Energy dispersive X-ray spectroscopy (EDS)

A commonly used method of implementing X-ray analysis in forensics, used for elemental analysis of a sample’s chemical composition by detecting and measuring the energy of X-rays emitted when the sample is hit by a high-energy particle beam, such as electrons, identifying the elements present by their unique characteristic X-ray signatures.

Focal point

One specific point that is used as a target for light when it goes through a lens.

Green primer

A type of primer that was introduced to reduce the environmental impact of heavy metals.

Gunshot residue (GSR)

A cloud of microscopic particles, including unburned gunpowder and primer residue, that are expelled from a firearm when it is discharged, depositing on the shooter’s skin and clothing and nearby objects, that can be analysed using SEM/EDS.

Immersion method

A technique used to compare glass fragments by immersing them in a liquid of a known refractive index (RI), used to find the liquid in which the glass fragment becomes nearly invisible, which indicates that the fragment’s RI is the same as the liquid’s RI.

Interference colours

Colours produced when light waves combine after reflecting from different surfaces of a thin film or passing through a birefringent material under polarized light.

Lacquer

A type of hard and usually shiny coating or finish used to protect and enhance surfaces like wood and metal, that dissolves in many organic solvents.

Michel-Lévy chart

An analytical working tool that relates the birefringence, thickness, and retardation properties, with which the analyst can use the observed colours and measured sample thickness to determine the birefringence, which is characteristic of the material.

Microanalysis

The application of a microscope and microscopial techniques to the observation, collection, and analysis of microevidence that cannot be observed or analyzed without such devices, such as samples in the milligram or microgram size ranges.

Micrometry

A method of determining dimensions and physical measurements using a specialized scale called a micrometer, used for things like measuring the thickness of the layers of a paint chip or the modification ratio of a synthetic fiber, or certain microchemical tests such as determining the identity of a grain.

Microspectrophotometry (MSP) / microspectrometry

An area of microscopy that has slowly become widely used in trace evidence analysis, using tools such as visible and infrared microspectrophotometers, which generate transmission, reflection, or absorption spectra from various translucent and opaque samples, and the spectrum is an objective quantitative characterization of colour that avoids human subjectivity. Examples of common uses are spectra obtained from coloured fibers and paint surfaces. 

Optical axis

The axis that passes through the center of an optical system, such as a lens or a mirror, representing its main axis of symmetry.

Plane polarized light

Light whose electric field vectors oscillate in a single plane, obtained using polymer films in which the molecules are highly oriented and have been treated with a dye to absorb light vibrating in almost all but one direction.

Polarizer

An optical filter that lets light waves of a specific polarization pass through while blocking light waves of other polarizations. It can filter a beam of light of undefined or mixed polarization into a beam of well-defined polarization.

Privileged direction

The specific vibration direction of light that is allowed to pass through a polarizing filter, which is crucial in polarized light microscopy.

Radial cracks

Cracks in a piece of glass that originate from the impact point and propagate away

Refraction

The bending of a wave as it passes from one medium to another, caused by a change in the wave’s speed, such as when it enters a new medium.

Refractive index

A measure of how much light bends, or refracts, when it passes from a vacuum into a substance, calculated as the ratio of the speed of light in a vacuum to the speed of light in that substance.

Retardation

The difference in velocities of light, specifically when one plane of light is converted into two vibrational planes perpendicular to each other, which travel through a substance at different velocities.

Secondary electrons (SEs)

Low-energy electrons ejected from a surface when a material is struck by a higher-energy beam, such as from an electron microscope. They’re crucial for imaging the surface topography of a sample, revealing details like cracks, pores, and edges.

Stereo binocular microscope

A type of microscope used to examine trace evidence, often used in the preliminary evaluation of submissions and for locating and recovering microscopic particles and materials from their substrates, such as fibers from a carpet in a car trunk.

Total magnification (TM)

The final magnification of an object when viewed through a compound microscope, calculated by multiplying the magnification of the eyepiece (ocular lens) by the magnification of the objective lens.

Vehicle

One of the materials in paint, that holds all the components together and is usually polymeric, consisting of natural or synthetic resins, which can form a surface film in many ways.