1. Metal and Paint Analysis

2. Atomic Structure Review
An atom is made of subatomic particles
Proton – positive (in the nucleus)
Neutron – No charge ( in the nucleus)
Electron – Negative (orbits around the nucleus)
When an atom has no charge, the number of protons equals the number of electrons

3. Isotopes
Atoms that are the same element (because they have the same number of protons), but differ in atomic mass (because they have a different number of neutrons)

4. Radioactivity the emission of energy from an atom in 1 of 2 ways:
electromagnetic waves (energy that moves through space)
as moving subatomic particles (electrons, protons, or neutrons)
Three types of Radiation defined by what is being emitted:
Alpha rays – 2 protons and 2 neutrons are emitted
Beta rays – electrons are emitted
Gamma rays – electromagnetic waves (neutrons)

5. 2 1 3

6. Metal Analysis
Neutron activation Analysis – used to identify trace elements in a sample
Bombard the sample with neutrons
Nucleus absorbs neutrons causing instability
Sample gives off gamma rays
The energy from the gamma rays is measured
Different elements have unique gamma ray energy values.
This will help identify the element. Then they measure the concentration of the element in the sample by measuring the intensity of the gamma ray energy.

7. Graph showing what elements are in a given sample.

8. Examples of using neutron activation
Used to characterize trace elements in metals, drugs, paint, soil, gunpowder residue, and hair.
Compare different types of copper wiring in a theft.

9. Examination of Paint Common in hit and run and burglary cases
Usually will compare 2 or more paints to establish where they came from.

10. Composition of Paint
Made of a binder, pigment and additives all dissolved in a solvent (solvent evaporates once paint dries)
Paint on a car:
Electrocoat Primer – 1st layer applied (black  gray)
Primer Surfacer – Corrosion control. Highly pigmented
Basecoat – Provides the color of the car
Clearcoat – Unpigmented to improve gloss, durability, and appearance.

11. Microscopic examination of paint
Crime scene and known specimens are best compared side by side under a stereoscope for color, surface texture, and color layer sequence.

12. Chemical analysis of Paint Binder
Pyrolysis gas chromatography
Heat paint sample to high temperatures so that they will decompose into numerous gas products.
Gas products flow through a chamber that separates them.
A chromatogram, or pyrogram is created and analyzed.
Enables criminalists to distinguish most paint formulations and the chemical makeup of the binder

13. Chemical analysis of Paint Pigments
Use the following to identify elements that make up a pigment:
Neutron activation analysis
Emission spectroscopy
Sample is heated to vaporize and excite sample’s electrons
Excited electrons emit light (different wavelengths based on energy of electrons)
Light is recorded and analyzed
Emission Spectroscopy

14. The Significance of Paint Evidence
Paint comparison
Identifying make and model of a car

15. Collecting and Preserving Paint Evidence
Picked up with tweezers or piece of paper
Stored in druggist folds, glass, or plastic vials
If on garments or objects, DO NOT REMOVE
Uncontaimnated standard/reference paint collected
Collect all layers