Forensics Chapter 13: metals, paints, and soil

neutron activation analysis

1. bombarding specimens with neutrons and measuring the resultant gamma-ray radioactivity 2. provides nondestructive method for identifying and quantitating trace elements 3. most sensitive method 4. drawback: expensive and regulatory requirements

layers of car paint

1. electrocoat primer- provides corrosion resistance. usually from black to gray 2. primer surface- smooth out and hide imperfections. highly pigmented 3. basecoat- provides color and represents the "eye appeal". integrity of layer depends on ability to resist weather, UV radiation, and acid rain. 4. clearcoat- applied to improve gloss, durability, and appearance. most are acrylic based

characterization of pigments

1. emission spectroscopy- can simultaneously detect 15-20 elements in most car paints. some are common and have little value; others are less common and used for comparing two paint specimens 2. ICP 3. x-ray spectroscopy

carbon arc emission spectrometry

1. instrument used to obtain and record the line spectra of elements 2. requires a means for vaporizing and exciting the atoms of elements so they emit light, a means for separating this light into its component frequencies, and a means of recording the resultant spectrum

radioactivity

1. particle and/or gamma ray radiation emitted by the unstable nucleus of some isotopes 2. composed of three types: alpha particles- radiation is composed of helium atoms minus their orbiting electrons beta particles- radiation consists of electrons gamma rays- high energy form of electromagnetic radiation emitted by a radioactive element

Characterization of paint binders

1. pyrolysis GC- paint chips decomposed by heat into numerous gaseous products and sent through a GC. Result is a pyrogram that is sufficiently detailed to reflect the chemical makeup of the binder. 2. IR spectrophotometry- binders selectively absorb infrared radiation to yield a spectrum that is highly characteristic of a paint specimen

Inductively coupled plasma emission spectrometry (ICP)

1. replaced carbon arc 2. identifies and measures elements through light energy emitted by excited atoms, but excites the atoms by placing sample in a hot plasma torch

Forensic examination of soil

1. side-by-side visual of color and texture 2. low-power microscope exam for presence of artificial debris 3. high-power microscope exam characterizes minerals and rocks 4. minerals- color, geometric shape, density, and refractive index useful for ID

line spectrum

1. type of emission spectrum showing a series of lines separated by black areas; each line represents a definite wavelength or frequency 2. a "fingerprint" of an element and offers practical method of identification

Paint as physical evidence is most frequently encountered​ in: A. A​ hit-and-run. B. Car theft. C. Burglary. D. Both A and B

A. a hit-and-run

Which of the following statements is true of examining the forensic properties of​ soil? A. Comparing rocks and minerals that are naturally present in soil provides evidential value. B. Due to the low number of distinguishable soil​ colors, color comparison of soil is done very rarely. C. A visual comparison of the color and texture of soil specimens is a long and intricate process. D. Color comparisons of soil samples can be done when the soil is wet

A. comparing rocks and minerals that are naturally present in soil provides evidential value

In a simple emission​ spectrograph, excitation of the specimen under investigation is accomplished with​ a(n): A. Electrical arc. B. Activated prism. C. Hot plasma torch. D. Inductive magnetic field.

A. electrical arc

Which of the following is a​ non-destructive technique for identifying and quantifying trace elements in a test​ sample? A. Neutron activation analysis B. ICP emission spectrometry C. Infrared spectrophotometry D. Carbon arc emission spectrometry

A. neutron activation analysis

The polymeric makeup of paint binders can readily be compared​ by: A. Pyrolysis gas chromatography. B. Emission spectroscopy. C. Thin-layer chromatography. D. Microscopy.

A. pyrolysis gas chromatography

Which type of radiation is NOT given off by radioactive​ decay? A. X- rays B. Beta particles C. Gamma rays D. Alpha particles

A. x-rays

Which property imparts paint with its most distinctive forensic​ characteristics? A. Gloss B. Color-layer sequence C. Texture D. Color

B. color-layer sequence

A​ "fingerprint" of an element is obtained by the technique​ of: A. Gas chromatography. B. Emission spectroscopy. C. Infrared spectrophotometry. D. Ultraviolet spectrophotometry.

B. emission spectroscopy

Neutron activation analysis involves bombarding specimens with neutrons and then measuring the​ resultant: A. Alpha particles. B. Gamma rays. C. Beta particles. D. X-rays.

B. gamma rays

Atoms having the same atomic number but different atomic masses are​ called: A. Isomers. B. Isotopes. C. Isotherms. D. Isobars.

B. isotopes

Which coat represents the​ "eye appeal"? A. Electrocoat primer B. Clearcoat C. Basecoat D. Primer surface

C. basecoat

Which coating helps resist UV radiation and acid​ rain? A. Primer surface B. Electrocoat primer C. Basecoat D. Clearcoat

C. basecoat

What is the logical first step in soil​ analysis? A. Use of the​ density-gradient tube technique B. Examination for presence of debris under​ low-power magnification C. Comparison of dried soil sample for color and texture D. Examination of minerals and rocks under​ high-power magnification

C. comparison of dried soil sample for color and texture

Which coating provides resistance to​ corrosion? A. Primer surface B. Basecoat C. Electrocoat primer D. Clearcoat

C. electrocoat primer

Gamma rays​ are: A. Neutrons. B. Protons. C. Electromagnetic radiation. D. Electrons.

C. electromagnetic radiation

An element is selective in the frequency of light it will absorb. This selectivity is due to​ its: A. Proton cloud. B. Number of neutrons. C. Electron energy levels. D. Atomic mass.

C. electron energy levels

The atoms of​ hydrogen, deuterium, and tritium all have the same number of​ protons, but differ in the number of neutrons they possess. These substances​ are: A. Elements. B. Molecules. C. Isotopes. D. Compounds.

C. isotopes

The nucleus of an atom​ contains: A. Protons and electrons. B. Neutrons. C. Protons and neutrons. D. Neutrons and electrons.

C. protons and neutrons

Which would be LEAST useful in identifying a mineral​ crystal? A. Geometric shape B. Color C. Size D. Refractive index

C. size

Which of the following statements is​ false? A. The proton has a charge of​ +1. B. The neutron has no electrical charge. C. The electron and proton have the same mass. D. Protons and neutron comprise the nucleus of an atom.

C. the electron and proton have the same mass

Which is NOT part of the composition of​ paint? A. Solvent B. Binder C. Pigment D. Adhesive

D. adhesive

Which of the following statements is​ correct? A. All atoms of an element have an equal number of neutrons and electrons. B. All atoms of an electron have the same number of neutrons. C. All atoms of an element have the same atomic mass number. D. All atoms of an element have the same number of protons.

D. all atoms of an element have the same number of protons

After examining small paint chips from an auto accident scene and using the PDQ​ database, the crime lab worker can determine the​ ________ of the vehicle. A. Year B. Make C. Model D. All of the above

D. all of the above

Radioactivity is composed​ of: A. Alpha particles. B. Gamma rays. C. Beta particles. D. All of the above

D. all of the above

What type of evidence would be expected to have trace​ elements? A. Paint and bullet fragments B. Soil and gun primer particles C. Glass and metal objects D. All of the above

D. all of the above

Automobile finishes typically contain which​ layer(s)? A. Clearcoat B. Colorcoat C. Electrocoat primer and colorcoat D. An electrocoat​ primer, colorcoat, and clearcoat

D. an electrocoat primer, colorcoat, and clearcoat

Paint binders can be chemically analyzed​ using: A. TLC. B. Pyrolysis GC. C. IR spectrophotometry. D. Both B and C

D. both b and c

Paint chips may be individualized to a single source by examining​ their: A. Ultraviolet spectra. B. Relative size. C. Infrared spectra. D. Color and layer structure. E. Pyrograms.

D. color and layer structure

The emission spectrograph is used to determine​ the: A. Mass of a substance. B. Weight of a substance. C. Crystalline structure of a substance. D. Elemental composition of a substance.

D. elemental composition of a substance

In neutron activation​ analysis, an element is identified by measuring the energy of​ emitting: A. Electrons. B. Protons. C. Neutrons. D. Gamma rays.

D. gamma rays

T/F: An atom has a net zero electrical​ charge, which indicates that it contains the same number of protons and electrons.

True

composition of paint

composed of a binder (polymeric substance) and pigments, and other additives all dissolved/dispersed in a suitable solvent

PDQ

database for info on paints related to automobile make, model, and year

T/F: A continuous spectrum is most helpful in identifying a particular element because it serves as a unique​ "fingerprint" of an element.

false

T/F: All atoms of an element have the same number of neutrons.

false

T/F: Alpha particles are a form of radiation consisting of electrons

false

T/F: Emission spectroscopy measures the frequency of light emitted by an atom when one of its electrons moves to a higher orbital.

false

T/F: If soil is found adhering to an​ object, the investigator should remove the soil particles from the object and send them to the laboratory.

false

T/F: Isotopes are atoms of the same element that have different numbers of protons in their respective nuclei.

false

T/F: It is not necessary that the collected paint from a vehicle involved in a​ hit-and-run accident be close to the area of the car suspected of being in contact with the victim.

false

T/F: Surface texture is the most important of the characteristics that a criminalist looks for when comparing paint chips.

false

T/F: The first step in a forensic soil comparison is analysis of the size of the particles.

false

T/F: The minerals found in different soil samples cannot effectively be used to determine whether or not they have the same origin.

false

T/F: The number of protons in the nucleus of an atom is called the atomic mass number.

false

emission spectrum

light emitted from a source and separated into its component colors or frequencies

nuclear forensics

responsible for developing ways to analyze nuclear materials recovered from either intercepted intact nuclear materials postexplosion debris as a result of a nuclear explosion

T/F: After the paint has been applied to a​ surface, the solvent evaporates.

true

T/F: Gamma rays are a​ high-energy form of electromagnetic radiation.

true

T/F: Isotopes have different atomic mass numbers.

true

T/F: Neutrons carry no charge.

true

T/F: Standard/reference soil samples should be collected at the site of the crime at various intervals within a​ 100-foot radius of the crime scene.

true

T/F: The concentration of the absorbing element is directly proportional to the quantity of the light absorbed.

true

T/F: The investigator should not try to remove trace paint evidence found on a tool but package the tool for laboratory examination instead.

true

T/F: The variety of coatings applied to the body of an automobile adds significant diversity to automobile paint and contributes to the forensic significance of automobile paint comparisons.

true

continuous spectrum

type of emission spectrum showing a continuous band of colors all blending into one another