Chapter 11 Trace Evidence II Isaac Tray

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

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

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

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

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.

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

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

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

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

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

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

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℉

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