1. Chapter 11 Trace Evidence II
Isaac Tray

2. Introduction C H
A P T E R 11
Manufactured products, as well as natural materials contain small amounts of trace elements
Trace materials are present in concentrations of less than 1 percent

3. How is trace evidence useful?
Trace elements are useful because they provide “invisible” markers that can determine the source of the material, or give additional points for comparison

4. Neutron Activation(metals)
Chemists use nuclear chemistry for providing a new tool to identify the elements in a material found
A nuclear reactor is a source of neutrons that are used to bombard atoms, causing radioactive isotopes*
To identify the isotope, it is necessary to measure the energy of gamma rays emitted
*Isotope: Atoms with the same number of protons, but a different amount of neutrons

5. Why is this useful?
This method is highly sensitive and nondestructive for simultaneously identifying 20 to 30 trace elements
Forensic analysis enables trace elements to be found in a crime scene, like metals, drugs, paint, and hair

6. Soil
Soil evidence is useful because it transfers from the crime scene to the criminal and will leave traces
Most soils can be differentiated by their appearance
This is done by placing the sample taken with a reference source, placing them side by side, and look for comparisons in color, texture, etc.

7. Soil examination
Forensic geologists will characterize and compare the mineral content in the soil
Some laboratories have density gradient tubes for comparison
Tubes are typically filled with layers of liquids that have different density values
When soil is added, it will sink to the portion of the tube that has a density of an equal value

8. Collection of Soil
Reference samples are collected at various distances at up to 100 yards of the crime scene
Soil found on the clothing/shoes of a suspect should not be removed
Each object should be wrapped in paper individually and sent to the laboratory

9. Paint
When paint is spread onto a surface, it will dry into a hard film consisting of pigments
Most common type of paint examined is from automobiles
Automobile paint normally has a variety of codings which makes the paint easier to identify

10. Paint Comparison
Compared under a stereoscopic microscope for color, surface texture and color layers
Chromatography can be used after for further examination

11. Paint Comparison
The elements within paint pigments can be identified by emission spectroscopy or X-ray spectroscope
Having the make and model of the car will make it easier to identify, as well as be able to look at color charts and finishes for that car

12. Emission Spectrograph
Emission spectrographs vaporizes and heats paint samples to high temperatures, so that atoms achieve their excited state
The excited atoms will emit light, the light is separated into components on a line spectrum
Each element present in the spectrum can be identified by its characteristics and frequencies
Emission spectrograph results can be compared to known samples

13. Inductively Coupled Plasma (ICP)
In ICP, the paint sample found is introduced into hot plasma
This creates charged particles that emit light of certain wavelengths that correspond to the elements present
ICP is commonly used in the identification and characterization of damaged bullets
The torch used to get the sample hot enough, up to 10,340℉

14. Collection and Preservation
Paint chips are usually found on an individual or at objects hit during the incident
Paper druggist folds and glass/plastic vials are excellent containers
Paint smeared or embedded require the entire item to be sent to the laboratory
Reference samples must always be collected