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Aberdeen Proving Ground, MD, United States

Kunz R.R.,Lincoln Laboratory | Gregory K.E.,Lincoln Laboratory | Aernecke M.J.,Lincoln Laboratory | Clark M.L.,Lincoln Laboratory | And 2 more authors.
Journal of Physical Chemistry A | Year: 2012

The chemical and physical fates of trace amounts (<50 Îg) of explosives containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3, 5-triazine (RDX), and pentaerythritol tetranitrate (PETN) were determined for the purpose of informing the capabilities of tactical trace explosive detection systems. From these measurements, it was found that the mass decreases and the chemical composition changes on a time scale of hours, with the loss mechanism due to a combination of sublimation and photodegradation. The rates for these processes were dependent on the explosive composition, as well as on both the ambient temperature and the size distribution of the explosive particulates. From these results, a persistence model was developed and applied to model the time dependence of both the mass and areal coverage of the fingerprints, resulting in a predictive capability for determining fingerprint fate. Chemical analysis confirmed that sublimation rates for TNT were depressed by UV (330-400 nm) exposure due to photochemically driven increases in the molecular weight, whereas the opposite was observed for RDX. No changes were observed for PETN upon exposure to UV radiation, and this was attributed to its low UV absorbance. © 2012 American Chemical Society. Source

Emmons E.D.,SAIC | Guicheteau J.A.,Research and Technology Directorate | Fountain III A.W.,Research and Technology Directorate | Christesen S.D.,Research and Technology Directorate
Applied Spectroscopy | Year: 2012

Raman cross-sections of explosives in solution and in the solid state have been measured using visible and near-infrared excitation via secondary calibration. These measurements are valuable for both fundamental scientific purposes and applications in the standoff detection of explosives. The explosive compounds RDX, HMX, TNT, 2,4-DNT, 2,6-DNT, and ammonium nitrate were measured using discrete excitation wavelengths ranging from 532 nm to 785 nm. A comparison of the spectral features and cross-sections between the solid state and solution was performed. Comparison is also made to cross-sections measured with deep ultraviolet excitation. © 2012 Society for Applied Spectroscopy. Source

Tripathi A.,SAIC | Emmons E.D.,National Research Council at the Research and Technology Directorate | Wilcox P.G.,Research and Technology Directorate | Guicheteau J.A.,Research and Technology Directorate | And 3 more authors.
Applied Spectroscopy | Year: 2011

We have previously demonstrated the use of wide-field Raman chemical imaging (RCI) to detect and identify the presence of trace explosives in contaminated fingerprints. In this current work we demonstrate the detection of trace explosives in contaminated fingerprints on strongly Raman scattering surfaces such as plastics and painted metals using an automated background subtraction routine. We demonstrate the use of partial least squares subtraction to minimize the interfering surface spectral signatures, allowing the detection and identification of explosive materials in the corrected Raman images. The resulting analyses are then visually superimposed on the corresponding bright field images to physically locate traces of explosives. Additionally, we attempt to address the question of whether a complete RCI of a fingerprint is required for trace explosive detection or whether a simple non-imaging Raman spectrum is sufficient. This investigation further demonstrates the ability to nondestructively identify explosives on fingerprints present on commonly found surfaces such that the fingerprint remains intact for further biometric analysis. © 2011 Society for Applied Spectroscopy. Source

Tripathi A.,SAIC | Jabbour R.E.,Research and Technology Directorate | Guicheteau J.A.,Research and Technology Directorate | Wilcox P.G.,Research and Technology Directorate | Snyder A.P.,Research and Technology Directorate
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Raman microspectroscopy and principal component analysis are used to decipher unique biomolecular information by monitoring the effect of residence time of Bacillus spores suspended in deionized water. Suspensions of viable spores of Bacillus anthracis Sterne (BA), Bacillus atrophaeus (BG), and Bacillus thuringiensis were prepared and spectrally monitored from initial deposition (time zero) and intermittently for seven days. Questions addressed include if spectral variations are significant with bacterial species and residence time under non-germination conditions, is the discrimination capability affected, and are there markers indicating pre-germination activity. Clear spectral distinction for the spore suspensions was observed with respect to residence time, however, when the residence time data were combined, discrimination analyses showed significant overlap between the BA and BG spores. Temporal spectral analyses at select wavenumbers suggest an increase in pre-germination activity from the freshly suspended to one day suspensions. © 2012 SPIE. Source

Guicheteau J.A.,Research and Technology Directorate | Swofford H.,U.S. Army | Tripathi A.,SAIC | Wilcox P.G.,Research and Technology Directorate | And 4 more authors.
Journal of Forensic Identification | Year: 2013

Through a collaborative effort between the United States Army Edgewood Chemical Biological Center (ECBC) and the United States Army Criminal Investigation Laboratory (USACIL), the ability to perform sequential Raman chemical imaging (RCI) and biometric analysis on fingerprints for rapid identification of threat materials and individuals was demonstrated. The chemical analysis and imaging of the fingerprints are achieved simultaneously through RCI. The fingerprint image, which bears the location and identity of the threat materials embedded within the fingerprint residue, is also suitable for subsequent biometric analysis through an automated fingerprint identification system (AFIS). In our tests, AFIS consistently generated a candidate list containing the source of the fingerprint in the top ranking position. These results mark the first step towards the practical application and implementation of RCI for chemical and biometric analyses on fingerprints routinely obtained at security checkpoints or developed during forensic counter-terrorism and drug investigations. Source

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