physical methods in forensic science exam 2

trace evidence

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

BLANK are normally the first examinations performed at the first FBI lab

microscopic comparison of fibers and hairs

earliest and simplest microscope was the single lens commonly referred to as a BLANK

magnifying glass

refraction

an abrupt change in direction of the beam is observed as a consequence of the difference in the velocity of light in the two media

visual image

can be seen only by looking through the lens

real image

can be seen directly (naked eye)

types of microscopes

compound microscope

comparison microscope

stereoscopic microscope

polarizing microscope

microspectrophotometer

scanning electron microscope (SEM)

compound microscope

constructed of two lenses mounted at each end of a hollow tube

for compound microscope, object to be magnified is placed under the BLANK

lower lens (objective lens)

for compound microscope, the magnified image is viewed through the BLANK

upper lens (eyepiece lens)

objective lens forms BLANK

real, inverted, magnified image of the object

eyepiece further magnifies the image into the BLANK

virtual image, which can be seen the eye

parts of compound microscope

base

arm

stage

body tube

coarse adjustment

fine adjustment

illuminator/light source

condensor

objective lens

eye piece or ocular lens

stage

a horizontal plate where the samples are placed to be examined

fine focus adjustment

focuses the microscope lenses (raises and lowers stage) on the specimen at a smaller magnitude

arm

supports the microscope and acts as a handle for carrying

light source

illuminates the specimen that is being examined

eyepiece/ocular lens

magnifies the image produced by the microscope’s objective

course focus adjuustment

focuses the microscope lenses on the specimen by raising and lowering the body tube or stage by larger magnitudes

diaphragm, iris, condenser

adjust the brightness and contrast on the specimen

nosepiece/turret

hold objective lenses in place

base

the support on which the instrument rests and assists in transporting

body tube

serves as a corridor through which light passes from one lens to another, the objective and eyepiece lenses are mounted on opposite lenses

objective lenses

to capture light emitted or reflected by specimen

stage clip

to securely hold the specimen in place

the compound microscope uses BLANK

transmitted illumination

transmitted illumination

light passes up from the condenser and through the specimen (bottom to top)

vertical or reflected illumination

illumination of a specimen from above; in microscopy it is used to examine opaque specimens (top to bottom)

compound microscopes can view

glass, body fluids, cells (transparent & translucent samples)

compound microscope has up to BLANK

1500x magnification

the magnifying power of a microscope is determined by BLANK

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

ocular lens =

10x

field of view

what the examiner sees when looking through the eyepiece

depth of focus can be BLANK

adjusted

lower magnification = 

higher depth of focus

higher magnification =

lower depth of focus

comparison microscope can be used to BLANK

compare two specimens

comparison microscope is essentially BLANK

two microscopes connected by an optical bridge

comparison microscope uses BLANK

vertical illumination (top to bottom)

comparison microscopes can compare these specimens side by side

bullet, cartridges, hairs, fibers (translucent & opaque evidence)

when looking through the eyepiece lenses of a comparison microscope, a circulare field, BLANK, is observed

equally divided into two parts by a fine line

stereomicroscope is the ideal instrument for location BLANK

trace evidence in debris, garments, weapons, or tools

a stereomicroscope has BLANK

a wide field of view

long working distance

great depth of focus

the most frequently used and versatile microscope in crime lab

stereomicroscope

stereomicroscope provides BLANK

10x to 125x magnifying power

stereomicroscope presents BLANK

distinctive 3D image of object

polarizing microscope uses BLANK

the difference in how light travels through minerals if different directions

polarizing microscope can distinguish between BLANK

isotropic and anisotropic materials

pleochroism

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

amorphous materials

minerals whose atoms are arranged in random order

crystalline materials

minerals whose atoms are arranged in a distinct order

examples of isotropic materials

gasses, liquids, cubic crystals

isotropic materials 

same optical properties observed from any direction

examples of anisotropic (or birefringent) materials

quartz, calcite, asbestos

anisotropic (or birefringent) materials

arrangement 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 chances

microspectrophotometer combines BLANK

the capabilities of a spectrophotometer with those of a microscope

with a microspectrophotometer, the microscope BLANK

magnifies the image of the specimen

with a microspectrophotometer, the spectrophotometer BLANK

measures the intensity of light at each wavelegnth

scanning electron microscope (SEM) is used when BLANK

evidence is extremely small and more magnification is needed

SEM can magnify an image BLANK

100,000x

SEM has a depth of focus more than BLANK of an optical microscope

300x

SEM sends BLANK

beams of electron

SEM can view

fine details

hair is strong corroborative evidence for placing an individual at the scene of a crime when:

1. it is properly collected at crime scene

2. enough reference samples have been submitted to lab

hair is primarily made of BLANK

keratin

3 layers of hair shaft

medulla

cortex

cuticle

cuticle

outside layer, overlapping keratin cells

cortex

middle layer

medulla

innermost layer

types of cuticle patters

coronal

spinous

imbricate

what pattern is this

coronal (crown-like)

what pattern is this

spinous (petal-like)

what pattern is this

imbricate (flattened-scale)

example of imbricate pattern

human

example of coronal pattern type

rodents and bats

example of spinous pattern type

cats

ways to study scale patterns

1. viewing under scanning electron microscope (SEM)

2. make a cast of the scale surface

how to make cast of scale surface

1. embed hair in soft medium (clear nail polish or softened vinyl)

2. when medium harden, remove hair

3. clear, distinct impression of cuticle is left

4. can now be examined by compound microscope

cortex is made of BLANK aligned in a regular array, parallel to the length of the hiar

spindle-shaped cells

cortex is embedded with pigment granules giving hair its BLANK

color

the color, shape, and distribution of granules of the cortex provide points for BLANK

forensic comparison

steps for forensic comparison of cortex

1. hair mounted in liquid medium with RI close to that of hair

2. structural features examined under microscope

3. amount of light reflected off hair’s surface is minimized

4. amount of light getting through hair is optiminized

the medulla is a BLANK

concentration of cells resembling a central canal running through center of cortex

types of medulla

continuous, interrupted, fragmented

most animals have BLANK or BLANK medulla

continuous or interrupted

presence of medulla BLANK even from hair to hair

varies

human head hairs generally have BLANK or BLANK

no medulla or it may be fragmented 

humans and most animals have what shaped medulla

cylindrical

cats have what shaped medulla

string of pearls

deers have what shaped medulla

spherical cells occupying entire hair shaft

medullary index

measures diameter of the medulla relative to diameter of the hair shaft

equation for medullary index

diameter of medulla / diameter of hair shaft

humans’ medullary index is BLANK

< 1/3

most other animals medullar index is BLANK

> 1/2

hair growth phases

anagen

catagen

telogen

anagen

actively growing phase

may last up to 6 years

when pulled from root, some hairs have follicular tag

we need the BLANK in hair

follicular tag

follicular tag contains BLANK

richest source of DNA associated with hair

catagen

transition stage between anagen and telogen

lasts only 2-3 weeks

hair continues to grow at decreasing rate

telogen

final growth phase

lasts 2-6 months

hair pushed out follicle

hair shedding