Experimental Explosive Characterization for Counterterrorist Investigation

D. Etayo, 

I. Maestrojuan, 

J. Teniente, 

I. Ederra, 

R. Gonzalo

Abstract

A THz spectral characterization of different explosives of special interest for the Spanish National Security Forces “Guardia Civil” is presented in this paper. This forensic analysis has been done in the frequency range from 0.060 THz to 3.5 THz using the Teraview TPS Spectra 3000 system in laboratory conditions. With this equipment the refractive index, absorbance and complex permittivity of the explosive samples have been obtained. In this study, some of the most common used explosives (Bullet gunpowder, mine gunpowder, PETN, TNT, RDX) are analysed paying special attention to differences related to the manufacturing process used to elaborate some of them and to the purity of the samples. The different fabrication processes of the explosives lead to the same spectral behaviour and characteristics. At the same time, the inclusion of some additives in the explosive samples does not alter their main electromagnetic properties. The sensitivity limit of the measurement system has been found to be to 10 mg of explosives. These results will be used to design future THz imaging systems that allow to detect and identify them in security and defence applications and/or to complete laboratory studies after a terrorist action.

Terahertz spectra of explosive materials

We have been asked for a reference for the terahertz spectra of explosive materials.


Below is a paper that was written a number of years ago been and is still of interest


The very far-infrared spectra of energetic materials and possible confusion materials using terahertz pulsed spectroscopy
Vibrational Spectroscopy 42(2)243-248(2006).
T. Lo, I.S. Gregory, C. Baker, P.F. Taday, W.R. Tribe, M.C. Kemp 

Abstract

We have measured the terahertz absorption spectra of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), pentaerythritol tetranitrate (PETN), 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX), 2,4,6-trinitrotoluene (TNT), the plastic explosives Semtex H, SX2, and Metabel, and a number of confusion materials using terahertz pulsed transmission spectroscopy. Spectral fingerprints were obtained from 3 to 133 cm⁻¹. The spectra of the plastic explosives are dominated by the spectral signatures of their explosive components due to low frequency vibrations and crystalline phonon modes. Importantly, the terahertz spectra of the confusion materials show no resemblance to the explosives spectra. The refractive indices obtained for the plastic explosives and confusion materials allowed us to derive reflectance spectra, which appear distinct and so suggest that terahertz reflection spectroscopy is a suitable tool for the detection of concealed explosives in security applications.

The full paper can be found at http://www.sciencedirect.com/science/article/pii/S0924203106000439


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