Physical Methods Exam 2

The magnified image produced by lens is called the virtual image

True-micro

The objective lens of a microscope produces a “real image,” or inverted image

yes-true

Which of the following is considered trace evidence

describe small, often microscopic, objects that are readily transferred between people and places

Polarizing microscope

forensic scientist wants to view light altering minerals in soil

comparison microscope

forensic scientist wants to compare bullet fragments from the scene and suspect simultaneously

Compound light microscope

forensic scientist wants to view blood cells

Stereoscopic microscope

forensic scientist uses this to search for trace evidence on the surface of a shirt

Which of the following is microscopes has the largest working distance?

Stereoscopic microscope

Although crime scene searches may initially focus on large objects, trace evidence must not be…

overlooked

Trace evidence is a generic term used to describe

small, often microscopic, objects that are readily transferred between people and places

Microscopic comparison of fiber and hairs was among the first examinations performed a the

FBI laboratory

Optical instruments using a lens or combination of lenses to magnify and resolve fine details of an object

Basics of the Microscope

Earliest and simplest microscopes was the single lens commonly referred to as the

magnifying glass

Why are things bigger under magnifying glass

This is due to the way light rays are refracted, or bent, in passing from the air into the glass and back into the air

Refraction

when light passes at an angle through the interface between two transparent media of different densities, an abrupt change in direction (refraction) of the beam is observed as a consequence of the difference in the velocity of light in the two media

Virtual image

can be seen only by looking through a lens and cannot be viewed directly

Real image

can be seen directly, like the image projected onto a motion picture screen

Constructed of ____ lenses mounted at each end of a hollow tub

two

objective lens forms

real, inverted, magnified image of the object

Transmitted illumination:

light that passes up from the condenser and through the specimen

Vertical or reflected illumination:

illumination of a specimen in microscopy it is used to examine opaque-up to 1500x magnification

Objective lens

Lower lens in the tube

Ocular Lens

Eyepiece

The objective lens produces a

“real” image

The magnifying power of a microscope is determined by

multiplying the power of the objective lens by the power of the ocular lens

Mechanical system includes:

base, arm, body tube, stage, and coarse and fine adjustment

illuminators

can be tungsten, fluorescent, halogen, or LED

In the condenser,

light rays from the illuminator are focused through a lens in the center of the stage and onto the specimen

Field of View

is what the examiner sees when looking through the eyepiece

Depth of focus

can be adjusted

Comparison microscopes are essentially

two compound microscopes connected by an optical bridge

Uses a bridge incorporating a series of ____ and ____ to join two independent objective lenses into a single binocular unit

mirrors and lenses

Stereomicroscopes

Details characterizing structures of many types of evidence do not always require examination under very high magnifications

Stereo microscopes provide

10x to 125x magnifying powers

Most frequently used and versatile microscope in a crime lab is the

stereomicroscope because its gas

stereo microscope is the ideal instrument for locating

trace evidence in debris, garments, weapons, or tools due to its wide field of view working distance and great depth of focus

Polarizing Microscope

Light travels through minerals in different directions but behaves predictably. The differences can be detected with a

Polarizing microscope- Analysis can provide information on

shape, color, and size of different minerals. Can also distinguish between isotropic and anisotropic materials

Pleochroism

is the property that causes a substance viewed under a polarizing microscope to show different absorption colors when it is exposed to polarized light coming from different directions

Minerals whose atoms are arranged in random order are classified as

amorphous materials

Minerals whose atoms are arranged in a distinct order are classified as

crystalline materials

Isotropic materials

have the same optical properties when observed from any direction (gasses, liquids, cubic crystals)

Anisotropic (or birefringent) materials (quartz, calcite, asbestos) are crystalline. The arrange of atoms is not the same in…

all directions and thus the arrangement of atoms in the substance appears to change as the direction of observation changes

A microspectrophotometer

combines the capabilities of a spectrophotometer with those of a microscope

The spectrophotometer then measures the intensity of

light at each wavelength

Scanning Electron Microscope (SEM)

Used when evidence is extremely small and more magnification is needed. Can magnify an image 100,000x; depth of focus more than 300x that of an optical microscope

Stage:

This is the platform that is used to support the specimen that is being examined. With the use of the x- and y- axis knobs, the scientists are able to move the specimen around on the stage to view different parts of it.

Fine Focus Adjustment

A knob that adjusts the height of the body tube in small

increments in order to bring the specimen into fine focus.

Arm:

A metal piece that supports the tube body of the microscope. This is also the spot that is utilized to pick up and move the microscope

Light Source:

The light source or the illuminator provides a controlled light source that helps to illuminate the specimen, creates contrast, enhance visibility, and allow for details to be accurately observed

Eye Piece Lens/Ocular Len

the function of the ocular lens is to view the real image through it; this is the smaller lens at the other end of the hollow tube in the eye piece. This lens produces a virtual image in the brain of the viewer. *Virtual image is a magnified image produced in the viewer’s mind of the real image, it has the same orientation as the real image, but its magnification is that that exceeds the magnification of the real image by the ocular lens.

Coarse Focus Adjustment

A knob that focuses the microscope on the specimen by raising and lowering the body tube of the microscope

Diaphragm or Iris or Condenser

focuses and directs the light onto the specimen. This allows for the control of angle and amount of light that is on the specimen, affecting contrast, resolution, and depth of field

Nosepiece/turret:

a rotating component on the microscope, that has multiple objective lens, allowing for quick switching between magnifications while keeping the lenses focused and aligned.

Base

The stand that the microscope sits on. Its primary function is basically to act as the spot that the microscope can be set on things at.

Body Tube

the hollow tube that holds the objective lens at the lower end and the eyepieces lens at the upper end. Its function is to hold the lenses while also allowing for light to pass from the objective lens through the body tube to the eyepiece, allowing it to be observed by the eyes

Objective Lens:

The lower lens in the hollow tube, that produces a “real image, “which is an inverted and magnified version of the specimen that is being examined. Its primary function is to produce this “real image.”

Stage Clip

The stage clips function to hold slides or an object that is on the microscope so that it does not move around when it is trying to be examined.

Stereoscopic microscope- appropriate

A drop of suspected blood on a shirt

Appropriate Microscope-Comparison Microscope

Cartridge cases from the scene and from the suspect’s gun

Appropriate Microscope-Compound Microscope

blood cells

Appropriate Microscope-Polarizing Microscope

A sample of soil found at the crime scene

Appropriate Microscope-Scanning Electron Microscope

A close up of a strange of hair, showing all fine details

The innermost layer of hair is called the cuticle

False the innermost layer of the hair is called the medulla

Name this cuticle scale pattern

imbricate

Is this hair from an animal

Which of the following is NOT a synthetic fiber? Rayon, acrylic, cotton, and nylon

Cotton

Paint evidence should be collected using forceps

True-hair

The primary protein in hair is

keratin

Structures of the hair

medulla=the lead, cortex=the wood, and cuticle=the paint on the outside

Cuticle

Scale structure covering the outside of the hair. Characteristic pattern.

Coronal

(or crown like) scale pattern

Spinous

(or petal-like) scale pattern

Imbricate

flattened-scale pattern

How to study the scale patterns?

1. 1. View under the Scanning Electron Microscope (SEM)

2. 2. Make a cast of the scale surface (clear nail polish or softened vinyl), when medium has hardened remove hair, clear distinct impressions of the hair’s cuticle are left. Can then be examined with a compound microscope

Cortex

Made-up of spindle-shaped cells aligned in a regular array, parallel to the length of the hair. Embedded with pigment granules giving hair its color. Color, shape, and distribution of granules provide points for forensic comparison. hair mounted in a liquid medium with RI, structural features examined microscopically, amount of light reflected off hair’s surface is minimized, and amount of light getting through the hair is optimized.

Medulla

Concentration of cells resembling a central canal running through center of cortex. Forensic analysis of: Structure: continuous, interrupted, and fragmented. Most animals have a continuous of interrupted medulla, presence of medulla varies even from hair to hair

Human head hairs

Generally, no medulla or it may be fragmented

Exception to human:

Mongoloid race whose medulla is usually continuous

Medulla 2. Shape

Humans and most animals have cylidicical.

Cats:

Resemble a string of pearls

Deer:

Spherical cells occupying entire hair shaft

Medulla-3. Medullary Index

Measures diameter of the medulla relative to diameter of the ahir shaft. Normally expressed as a fraction: Diameter of medulla/diameter of hair shaft.

medullary index <1/3

Humans

Medullary index >1/2

Most other animals

Anagen

Actively growing phase

Catagen

Transition stage between anagen and telogen phases

Telogen

Final growth phase in which the hair naturally falls out of the skin

Anagen phase info

May last up to 6 years, Root is attached to follicle for continued growth. Root bulb has a flame-shaped appearance. When pulled from root, some hairs have a follicular tag

Follicular Tag

Translucent piece of tissue surrounding the hair’s shaft near the root. Contains richest source of DNA associated with the hair

Telogen Phase-Info

Lasts 2-6 months, hair is pushed out of the follicle, causes the hair to be naturally shed

Catagen phase-information

Transition phase between anagen phase and telogen phase. Lastly 2-3 weeks. Hair continues to grow, but at a decreasing rate. Root bulb shrinks and is pushed out of the follicle. Root typically takes an elongated shape

Microscopic Comparison of Hair- Prime purpose for examining hair evidence in a crime laboratory is to

1. Establish whether the hair is human or animal.

2. Determine whether human hair from a crime scene

compares with hair from a particular individual by

looking at: Color, Length, Diameter, Damage, Distribution, shape, and color intensity of pigment granules, Dyed or bleached hair, Presence/Absence of medulla

Collecting Hair Evidence

Should be collected by hand, using a bright light to illuminate the search area. Collect using tweezers/forceps, transparent tape, lint roller, or evidence vacuum. Package individual hairs in paper packets. Package the entire piece of tape or lint roller in polyethylene storage bag. Collect control/reference samples (plucked preferred) from all pertinent areas of the body. Begin collecting hair evidence ASAP

Questioned hair samples submitted in laboratory_______be accompanied by adequate number of refence samples: Victim of the crime, individual suspected of having deposited hair at the crime scene

MUST ALWAYS

Reference samples ____come from the _____area of the body as questioned samples

must, same

Important that collection is carried out in a way to ensure a——————— of hair from any area of the body

Representative sampling

Information Obtained by Microscopic Comparison of Hair

Can possibly determine the area of the body from

which the hair originated. Cannot reveal age or sex of individual (aside from infant hair, which alludes to the age range). Analysis may be able to suggest the race of the

hair’s owner.

Most fibers of forensic interest are very common and encountered daily in

homes and workplaces

Evidential value depends on

ability to narrow their origin to a limited number of sources or even to a single source