Vibrational spectroscopy standoff detection of explosives.

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Chemical Sensing

Background:

• Remote detection of high explosives (HE) is crucial for security applications.
• Standoff detection methods are needed to minimize risk to personnel.
• Existing spectroscopic techniques have limitations in standoff capability and sensitivity.

Purpose of the Study:

• To design and test standoff infrared and Raman spectroscopy (SIRS and SRS) systems for remote detection of high explosives.
• To determine the limits of detection (LOD) for various HEs using both SIRS and SRS.
• To evaluate the performance of these systems at different standoff distances and with varying sample types.

Main Methods:

• SIRS system: Fourier-transform infrared interferometer coupled to a gold mirror and detector for active reflectance mode.
• SRS system: Fiber-coupled spectrograph and reflective telescope for remote spectral acquisition.
• Sample preparation: Thin films (2-30 microg/cm(2)) on stainless steel for SIRS, particles (3-85 mg) for SRS.
• Target compounds: Nitroaromatic HEs (TNT, DNT, RDX, C4, Semtex-H) and TATP.

Main Results:

• SIRS achieved LODs of 18 microg/cm(2) for TNT and 20 microg/cm(2) for RDX at the longest standoff distance.
• SRS detected as little as 3 mg of TNT and RDX at a 7 m distance using specific laser excitation wavelengths.
• The study reported the first detection and quantification of C4 formulation using these standoff techniques.

Conclusions:

• SIRS and SRS are effective methods for the remote detection of high explosives.
• The developed systems demonstrate promising sensitivity and standoff capabilities for security applications.
• Further optimization could enhance detection limits and expand the range of detectable explosives.