Rifle bullets comparison by wavelength dispersive X-ray fluorescence spectroscopy and chemometric analysis.

Area of Science:

• Forensic Science
• Analytical Chemistry
• Materials Science

Background:

• Bullet lead examinations are discontinued by the FBI, necessitating alternative methods for origin identification.
• Bullet composition analysis has shown promise in case studies for determining bullet origin.

Purpose of the Study:

• To analyze rifle bullet composition using WDXRF and chemometrics.
• To identify spectral similarities among bullets from different manufacturers.

Main Methods:

• Wavelength dispersion X-ray fluorescence (WDXRF) was employed for elemental analysis.
• Chemometric methods, including Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), k-nearest neighbor (k-NN), and Soft Independent Modeling of Class Analogy (SIMCA), were used for data analysis.
• X-ray scattering spectra were utilized for the first time in fragment analysis.

Main Results:

• PCA effectively discriminated bullets from five different manufacturers, with three principal components explaining over 99% of the variability.
• The spectral region for Antimony (Sb) and the scattering region were critical for group discrimination.
• HCA formed five distinct clusters corresponding to the manufacturers.
• k-NN and SIMCA achieved 100% correct classification of test set samples.
• X-ray scattering analysis contributed to grouping bullets from the same manufacturer.

Conclusions:

• WDXRF combined with chemometrics is a suitable technique for forensic bullet origin analysis.
• The method is quick, relatively simple, and preserves evidence.
• The study demonstrates the potential of WDXRF and chemometrics for discriminating bullet origins based on elemental composition.