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Forensics > Microscopy > Flashcards

Microscopy Flashcards

1
Q

What are microscopes?

A

Devices that produce magnified images of structures too small to see with the unaided eye

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2
Q

What are the 3 primary types of microscopes?

A
  1. Compound microscope
  2. Dissecting microscope
  3. Electron microscope
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3
Q

What does a compound microscope do?

A
  • produces a magnified image by focusing visible light rays
  • uses 2 lenses
  • can observe living or non living specimens
  • magnification ranges from 2.5 to 1300x
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4
Q

What limits the use of a compound light microscope?

A

Light must be able to pass through the specimen - s considerable preparation may be required

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5
Q

What is a comparative microscope?

A
  • type of compound microscope
  • two separate items can be viewed simultaneously under same lighting conditions and magnification
  • allows for meticulous comparison in court
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6
Q

When is a dissecting microscope used?

A

When viewing large specimens

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7
Q

What does a dissecting microscope do?

A
  • 3-D image is viewed
  • light does not pass through object but the surface is magnified and a light source allows adjustment to contrast imaging
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8
Q

What is the main disadvantage of a dissecting microscope?

A

Lower magnification than compound microscope

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9
Q

What is the main advantage of a dissecting microscope?

A

Evidence rarely requires pre-treatment

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10
Q

What does an electron microscope do?

A
  • focuses beams of electrons to magnify and image
  • magnifies 1000x or more than a compound microscope
  • can not be used to study living specimens because they must be dried in a vacuum inside the microscope
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11
Q

What are the different types of electron microscopes?

A
  • scanning electron microscope
  • environmental scanning electron microscope
  • transmission electron microscope
  • scanning tunnelling microscope
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12
Q

What are the advantages of light microscopes? (5)

A
  • magnify details and spatial relationships of objects
  • no need for sample pre-treatment
  • ability to observe living cells
  • flexible sample types
  • image capture and storage
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13
Q

What is the disadvantage of light microscopes?

A

Low resolution

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14
Q

What are the advantages of electron microscopes? (4)

A
  • higher resolutions
  • all kinds of samples
  • alternative information
  • can image 3D external shape
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15
Q

What are some disadvantages of electron microscopes? (2)

A
  • elaborate sample preparation

- dry so cannot view living cells

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16
Q

What are light microscopes used for in forensics generally?

A

Used for comparison between evidence item and suspected linked object

17
Q

Examples of things light microscopes are used for in forensics

A
  • striations on bullets
  • tool marks
  • fingerprints
  • type impressions
  • manufacture marks
  • comparison of structure and colour of hair, clothing or plant fibres, paint fragments, biological specimens and skeletal trauma marks
18
Q

What is SEM generally used for in forensics?

A

For characterising surface structure and comparison of surface composition

19
Q

Examples of SEM uses in forensics

A
  • striations on bullets
  • composite soils (rocks, sediments, soils and dust)
  • insect taxonomic characteristics
  • paint comparisons
  • manufacture batch matching (eg glass, paper, tape and metals)
20
Q

What is the basic principle of SEM?

A
  • uses beam of electrons

- electron beam hits sample and interacts with samples - electrons are scattered

21
Q

What are secondary electrons?

A
  • ejection of loosely bound outer orbital electrons from specimen atoms by in elastic scattering
  • requires little energy for this and resultant secondary electrons have low energy
  • only SES produced near the surface are ejected and detected
  • reflect structural information
22
Q

What are back scattered electrons?

A
  • primary beam electrons elastically scattered by atom nuclei in the sample back out of the sample
  • have high energy
  • come from a larger volume within the sample
  • heavier elements = more scattering = more BSEs
  • reflect compositional information
23
Q

Regions of high atomic number will appear ….

A

Bright

24
Q

What is the magnification of SEM?

A

10 - 500,000x

25
Q

What is the resolution of SEM?

A

Up to 1nm

26
Q

What does the quality and resolution of SEM depend on?

A
  • instrument performance
  • selection of imaging parameters
  • nature of the sample

Forensics (18 decks)

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