The detection and identification of energetic materials and discrimination between energetic material and other materials is essential for our safety. However, many energetic materials contain similar functional groups (–NO2 and -N=N- for example) so InfraRed (IR) spectra may not be sufficiently different for discrimination. The development of terahertz far-infrared technology (THz/Far-IR) could enable standoff-analysis of a suspicious package to detect and identify materials without the direct handling of the package. We report the analysis of a range of energetic materials by IR (4000-500 cm-1) and THz/Far-IR spectra (600-10cm-1) in order to explore the potential and compare the discriminating power of THz/Far-IR to standard IR and gauge the potential of THz/FAR-IR as a safe screening technique. This project analysed explosives and precursors commonly found in military and Home Made Explosives (HMEs). Whereas IR determines the functional groups, Far-IR/THz determines the interactions and produced very distinct spectra below 400cm-1 that easily discriminated between different energetic materials and also between energetic materials and their precursors and also compounds similar to energetic materials. For example THz/Far-IR spectra of cyclic trimer RDX (-CH2-N-N-O2)3 and the cyclic tetramer HMX (-CH2-N-N-O2)4 and precursor, hexamine can be discriminated. THz/Far-IR also offers the ability to analyse through the packaging of the suspicious items as they are transparent in this region. Spectra taken at the Australian Synchrotron from polyethylene pellets, pellets of pure material and evaporated thin films showed good discrimination. Spectra were comparable to those from a Ultra-broadband air-plasma THz TDS System stand-off detector of up to 20 m. However, there were some spectra that show differences between European and Australian samples that needs further research. For example, the PETN from Europe has extra peaks around 15 THz that do not appear in the Australian PETN. These could be due to impurities or degradation products and will be investigated further. Computer modelling has also been undertaken in this region and produce similar absorbances to those observed at the Synchrotron. Far-IR/THz spectroscopy shows promise in detecting and discriminating between energetic materials, precursors and materials similar to, but different to, energetic materials and could be obtained through some normal packing materials.

THz/Far-Infrared spectroscopy at the Australian Synchrotron for the detection and identification of energetic materials and discrimination between energetic materials and precursors

2019 Fall National Meeting

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