Week 5 Flashcards
Wavelength of White Light
400 to 700 nanometers
Light is radiant energy, usually referring to electromagnetic radiation that is visible to the human eye and responsible for the sense of sight.
Luminesence
When a substance produces light without being heated
Two most common types of luminesence
1) Fluoresence
Emission of light that ceases the moment you remove the light source
2) Phosphoresence
Emission of light continues for some time later after exciting radiation is removed
- ie: Luminol or Blue Star
Creates contrast; eliminating the background
Ultraviolet (UV) Light
- Applications
1) Fibers
2) Some fluids
3) Inks
4) Fluorescent powders
5) Dye Stains
6) Bite Marks
7) Untreated Fingerprints
8) Treated Side of Glass
Safety: Forensic Light Sources
1) High intensity light
2) Refer to manufacture equip manual
3) Skin protection
- Gloves, long sleeves, etc
4) Eye protection
- Goggles for wavelength and intensity
5) Responsible for others on scene
What is the best light source for detection of crime scenes
Blue - 450 nm
- Footwear impressions
- Hair and fiber
- Bloodstains
- Latent prints
- Drugs, paint, grease
- Bones, teeth
- Bodily fluids: sperm, saliva, urine, blood
Why use chemicals
1) Elimination of background for better contrast
2) Inproved chances of finding impressions
3) Quality of impressions developed often are better
WHMIS label
1) Identity of the product
2) Safe handling information
3) Statement that SDS is available
9 factors to consider regarding chemicals: use or not to use
1) History of exhibit
- Dry, preciously wet, where found
2) Seriousness of the offence
3) Practicality
4) Value of the item
5) Damage to surrounding items
6) Substrate
7) Matrix
8) Time elapsed between deposition and development of print
9) Generally: more/better prints with chemicals
Sequence of treatments for a dry porous substrate
1) Visual examination (FLS/white)
2) Iodine fuming/Driodine
3) DFO or Indanedione/Zinc chloride
4) Ninhydrin
5) Silver nitrate
6) Oil red / Physical developer
Dry porous substrate
- Indanedione/Zinc chloride
1) Reacts with amino acids on porous substrates
2) Fluoresces with green light and orange filter
- Works better with laser
Wet porous substrate
- 2 methods to develop impressions
1) Oil Red “O” (ORO)
2) Physical developer
Only the lipids left on the surface
UV Light wavelength
3-400 nm
Clear goggles
Basic yellow wavelength
450-485
Orange goggles
R6G wavelength
505-535
Orange goggles
With laser… 532 and laser goggles (orange)
