Forensic Use Of Light Forensic Science - PowerPoint Presentation

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Forensic Use Of Light

Forensic ScienceSlide2

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Forensic Use of Light

Forensic Use of Light – an understanding of light energy, its properties, its uses, and its technological applications is fundamental in the study of forensicsLocation/Collection of Evidence with Light Observation of Evidence with Light Analysis of Evidence with

Light3Slide4

Wave Theory of

Light:

Light Waves vs. Sound WavesBoth travel

in the form of

wavesBoth are frequenciesOur eyes and ears cannot detect all of the frequenciesLight waves are much faster than sounds wavesSound waves require a medium to travel through, but light waves can travel through a vacuum4Slide5

Wave Theory of

Light:Wave Definitions

Wave – when some form of energy (light, sound, water) is transferred by a disturbance in a medium (light waves do not require a medium)Longitudinal (or compressional) waves – travel like a flexible

helical spring toy that somersaults down steps

(i.e. sound waves)Transverse waves –like ripples in a puddle (i.e. light waves)5Slide6

Wave Theory of Light:Wave Definitions (continued)

Wavelength (λ) – the distance from the top of one wave to the top of the nextLarger waves have a longer wavelengthSmaller waves have a shorter wavelengthThe unit used for light wavelength is the meter (m

)Wave Speed (c) – different wave mediums travel at different speedsThe speed of light is 3.0 x 1010 cm/s or 3.0 x 108 m/s (speed is considered as though in a vacuum)The unit of speed of a wave is meters/second

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Wave Theory of Light:

Wave Definitions (continued)Frequency

(v) – the number of waves that pass per unit of time; wavelength and frequency are inversely relatedLonger wavelength means shorter frequency and vice versaThe unit for frequency showing cycles per second is the Hertz (Hz)Frequency and wave energy are synonymous

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Wave Theory of Light:

Wave Definitions (continued)Wave Formula (

c = λν)Wave formula in words – speed equals wavelength times frequencySo the speed of a wave is a product of frequency and wavelengthSymbolsc = speed of the type of wave (can be the speed of

light)

λ = wavelength (meters)v = frequency (Hz)8Slide9

Wave Theory of Light:

Wave Definitions (continued)

Amplitude – the height of the wave from the bottom (trough) to the top (crest)Amplitude is also thought of as the energy the wave carriesWavelength, speed, and frequency do not change just because the height (amplitude) of the wave changes

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Low Frequency, Long WavelengthHigh Frequency, Short Wavelength

Amplitude*

Amplitude*Slide10

Wave Theory of Light:

Electromagnetic Spectrum

The entire range of known light waves is called the electromagnetic spectrum10

Increasing Wavelength

Increasing FrequencySlide11

Wave Theory of Light:

Electromagnetic Spectrum (continued)

There is an array of different light waves (electromagnetic radiation or “radiation”) with characteristic colors, invisibilities, wavelengths, and

frequencies

Radio waves and microwavesInfrared lightVisible SpectrumUltraviolet light (black light)X-rays and gamma rays11Slide12

Wave Theory of Light:Visible Spectrum

Light (sunlight/electric light bulb) or white lightAllows us to see

Is actually a combination of all known colorsCan be any color we seeAn object absorbs most of the visible wavelengths and reflects some of the wavelengths – this is what we see as color (i.e. plants absorb all wavelengths (colors) except for green)

Any object will absorb and reflect different light wavelengths depending on its composition

The chemical compounds the object is made ofOr the chemical compounds of the paint on the object12Slide13

Wave Theory of Light:

Forensic Use of the Electromagnetic SpectrumInvestigators

should use all forms of light possible when gathering evidenceRegular white light Ultraviolet (UV) light Infrared (IR) light A good forensic light source is made up of a powerful lamp containing all of the light wavelengths

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Particle Theory of Light

Light (electromagnetic spectrum) behaves like a wave in the way it travels; however, light also acts like a particle in the way it transfers energy to electrons This is called the Dual-Theory of Light14Slide15

Particle Theory of Light: Photons

Photon – an energized packet of light energyIn the late 1800’s/early 1900’s, scientists noticed light behaving sometimes like a wave and sometimes like particles This

idea of particles was combined with the Atomic Theory to create new light theories (Quantum Physics)Photons of light are absorbed (energy gained) and emitted (light is given off)15Slide16

Categories of Light Reactions:

Two Sources of Light In general, “light” refers to the portion of the electromagnetic spectrum that we seeIncandescence (hot) (i.e. light bulb)Luminescence (cold) (i.e. fluorescent lights)

ChemiluminescenceThermoluminescence PhotoluminescenceTwo Types that Absorb Ultraviolet EnergyFluorescencePhosphorescence

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Categories of Light Reactions:

PhosphorsPhosphors – any substance that causes an object to show photoluminescenceCauses certain objects to glow in the dark, or light up under UV

radiationUsed in radar detection and plasma screen TV’sExamples: rare earth minerals, transition metals, nucleic acids found in DNA, and biomoleculesBecause many different types of phosphors found in the human body and other types of forensic evidence, UV lights are irreplaceable

in evidence

collection17Semen under UV lightSlide18

Light Properties

Emission Absorption TransmissionReflectionRefractionDispersionIntensity DiffractionInterferencePolarization

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Light

Properties Forensic Uses:

Magnification PurposesMacro-View (magnifiers and stereomicroscopes)Micro-View

(compound microscope)

Microscopic Refractive Index Micro ColorimetryChromaticity Diagram Types and Techniques of MicroscopyBright Field Microscope Dark Field Microscope Phase Contrast Differential Interference Contrast (DIC) or Nomarski Microscopes Polarized Light Microscope Fluorescence Infrared/Ultraviolet Light Digital Microscopes Electron Microscopes Other Microscopes 19Slide20

Light Properties Forensic Uses:Types of Spectroscopy

A spectroscope uses prism or diffusion grating to break apart incoming wavelengths; the specific emission/absorption of wavelengths can be used to identify the unknown element in the composition of evidenceInfrared (IR) Spectroscopy Ultraviolet (UV) Spectroscopy

Reflectance Ultraviolet Spectroscopy (RUVIS) Raman Spectroscopy Microspectroscopy X-ray Diffraction/Absorption Atomic Emission/Absorption Spectroscopy Microwave Spectroscopy Types of Spectrometry that Don’t Use Light

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Light Properties Forensic Uses:Other Forensic Uses of EM Radiation

Nuclear Magnetic Resonance (NMR) – radio waves and magnetic fields are used to penetrate unknowns and collect information from hydrocarbonsValuable because it is nondestructive – evidence can still be analyzed again later

Can be used to analyze DNA and/or dangerous samples such as explosivesA form of NMR is used to determine time of death by finding brain metabolite levelsElectron Paramagnetic Resonance – uses microwave (not radio) waves for similar purposesX-ray Fluorescence, Neutron Activation Analysis (with infrared spectra), Inductive Couples Plasma – other examples of the many technological advances that use various forms of the EM spectrum to analyze and identify forensic evidence

samples

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Light Properties Forensic Uses:Other Forensic Uses of EM

Radiation(continued) Immersion Test – a transparent object (glass) is immersed in several liquids with known refractive indexes to compare the refractive indexesGlass

appears to be “invisible” or disappear in liquid that has the same refractive indexIf the liquid has a lower or higher refractive index than the glass, the glass can still be seen (with a halo around it)ExamplesMethanol RI = 1.33Glycerin RI = 1.47Clove Oil RI =

1.54

Pyrex Glass RI = 1.47 (would disappear in glycerin)Lead Glass RI = 1.56 (would disappear in clove oil)22Slide23

Light Properties Forensic Uses:Other Forensic Uses of EM Radiation

(continued) Immersion Test – a transparent object (glass) is immersed Other Large Scale Uses of Refractive IndexRefractometer

– determines the refractive index of various solids and liquidsUsed to determine the identity of unknowns in forensics Can be handheld for fieldwork or larger for a laboratory counterAlso used to determine the density of liquids and the concentrations of various components in the liquids (sugar in urine, drugs in the blood, etc.)

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Light Properties Forensic Uses:Other Forensic Uses of EM Radiation

(continued) Finding the Diameter/Width of a Minute Object – Thomas Young’s Double Split Patterns (interference/ diffraction of light): an experiment that showed that specific light patterns are dependent on the number of slits through which light is shownUsing

the known frequency of light and measurements of interference patterns you can determine the actual width of the solid that caused the light to splitTo find the diameter or width of an object: d = lL  10Sd = diameter of a minute object in micrometers (µm)

I

= wavelength of the light (nm) L= distance from the light source to the screen (m)S = the average distance between bands (cm) 24Slide25

Light Properties Forensic Uses:Other Forensic Uses of EM Radiation

(continued) Uses of Infrared Light (Thermal Radiation) – many materials are sensitive to thermal or infrared (IR) radiation (IR waves are longer waves in the EM spectrum)Used

in night vision goggles/equipmentMany types of crime scene evidence are located because they will absorb visible light and show IRIR luminescence is used for many types of document analysisIllegal AlterationErased Writing

IR

absorption or glow from different inksRevelation of charred document contentsUsed in conjunction with other technology25Slide26

Light Properties Forensic Uses:Other Forensic Uses of EM Radiation

(continued) Uses of Ultraviolet Light (Black Light)Mostly used in evidence

collectionMany bodily fluids (biomolecules) fluoresce when illuminated by a source of UV lightDetection of crime scene stains such as saliva, semen, vaginal fluids, urine, and perspirationMany times latent fingerprints will fluoresce for detection

purposes

UV light analysis is recommended as a first choice by the FBI for examining and identifying biological evidenceAlso used for authenticating signatures, paintings, and ink stainsUsed in the detection of trace evidence and illegal substancesUsed to see the light of luminol in order to find blood evidence26Slide27

Light Properties Forensic Uses:Other Forensic Uses of EM Radiation

(continued) Forensic Light SourceA powerful lamp with ultraviolet, visible, and infrared wavelengths of light that has many components to enhance

visualizationDirect lighting, such as a strong white light, is very useful to reveal trace evidenceOblique or parallel lighting will also reveal small particlesUsed with all types of magnifiers and microscopesA

multiple color band can penetrate many skin depths to reveal details of a bruise

patternWhite light is normally used first, with other wave lengths, chemicals, goggles, polarizers, and colored lenses are used after the initial observation27Slide28

Light Properties Forensic Uses:Other Forensic Uses of EM Radiation

(continued) Cameras use refraction and polarization properties (various lenses, including colored lenses) to capture permanent proof of evidence and its analysisUsed in evidence collection, observation, and analysis to record

resultsUsed withSpectroscopyScanning electron microscopesFluoresce of IR or UV radiation Luminol (to record the chemicaluminescence of a reaction with blood evidence)

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Forensics, Technology &

EvidenceLocation and Collection of Evidence with Light – light, and all of its sources, are used to locate evidenceExamples Flashlight

Ultraviolet or black lightLight sources with all wavelengths Colored goggles or filtersMany types of digital photography

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Forensics, Technology &

Evidence (continued)Observation of Evidence with Light – once evidence has been located and collected, light is used to observe itExamplesMagnifying glass

Microscopes (stereomicroscopes, polarizing microscopes, etc.)30Slide31

Forensics, Technology & Evidence (continued)

Analysis of Evidence with Light – science has made many discoveries about light, and these are applied to analyze forensic evidenceSome ExamplesMicroscopes of all types, including electron and ion microscopes

Spectroscopes – used to identify trace evidenceEmission spectroscopyGas and mass spectroscopyInfrared and ultraviolet applicationsMicrowave, X-Ray, and nuclear forms also

Mass

Spectrometry – identification purposesGas and liquid chromatography specializations31Slide32

Resources

Saferstein, Richard. Forensic Science: An Introduction. New Jersey: Pearson Prentice Hall, 2008.Bertino, Anthony J. Forensic Science: Fundamentals & Investigations. Mason, OH: South-Western Cengage Learning, 2009Deslich

, Barbara; Funkhouse, John. Forensic Science for High School Dubuque, Iowa: Kendall/Hunt Publishing Company, 2006Texas Education Agency, Forensic Certification Training, Sam Houston State UniversityDo an Internet search for a video using the following: Flame Test 07.

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