Personal Statement
Elemental Analysis of Forensic Material with the National Aeronautics and Space Administration and the National Institute of Justice X-ray Fluorescence Detector

Tiffany Fogg

Jacob I. Trombka

Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center


NASA, the National Aeronautics and Space Administration Goddard Space Flight Center, in conjunction with the National Institute of Justice (NIJ) have developed a break through in technological advancement for criminal justice agencies and space science. The portable yet non-destructive innovation known as the X-Ray Fluorescence, XRF, conducts analysis on samples collected from local agencies. The XRF method is primarily used to measure the elemental composition of materials. It is the most favorable alternative for field applications and industrialized production for control because of its fast and non-destructive design.

It is composed of an x-ray tube and a voltage multiplier that is attached within a brass cylinder. The target end is at ground potential and is to the left of the tube. The current of electrons in the tube is generated from a photo cathode at the right of the tube. The tube and voltage multiplier circuit are isolated from external surroundings by a clear lead based Plexiglas.

In XRF spectroscopy, an atom can either absorb the x-ray or it may be scattered throughout the material. Because each element has a distinctive set of energy levels, these elements will generate x-rays that are a unique set of energies, allowing scientist to non-destructively determine the elemental composition of a sample. The process of emissions of characteristic x-rays is called X-ray Fluorescence. The innermost valence shells, which are the K and L shells, are used in XRF detection. An x-ray spectrum from an irradiated sample will exhibit multiple peaks of varied intensities.

During the analysis, samples from a Gun Shot Residue database, GSR, provided significant support in determining minimal levels of antimony (Sb), barium (Ba), copper (Cu), lead (Pb), Tin (Sn), Zinc (Zn) and Titanium (Ti), all of which are distinguishable elements in the composition of ammunition with the XRF detector.

Paint is identifiable through x-ray fluorescence and is more finely tuned to the physical and elemental components. An analysis of paint chips was used to test the hypothesis that the XRF detector was used to provide significant evidence in the crime scene environment. In addition, the x-ray fluorescence demonstrated that the paint chips provide vital evidence of the elemental composition of paint on automobiles coherently.

The long-term goal was to focus primarily on the essential factors of GSR and paint chips on a non-destructive, portable device that will provide significant support for the NASA and the NIJ in determining key aspects of a crime scene.