The Development of a Semtex-H Simulant for Terahertz Spectroscopy

Abstract

The development and use of terahertz (THz) frequency spectroscopy systems for security screening has shown an increased growth over the past 15 years. In order to test these systems in real-world situations, safe simulants of illicit materials, such as Semtex-H, are required. Ideally, simulants should mimic key features of the material of interest, such that they at least resemble or even appear indistinguishable from the materials of interest to the interrogating technique(s), whilst not having hazardous or illicit properties. An ideal simulant should have similar physical properties (malleability, density, surface energy and volatility to the material of interest); be non-toxic and easy to clean and decontaminate from surfaces; be recyclable or disposable; and be useable in a public environment. Here, we present a method for developing such an explosive simulant (for Semtex-H) based on a database of THz spectra of common organic molecules, and the use of a genetic algorithm to select a mixture of compounds automatically to form such a simulant. Whilst we focus on a security application, this work could be applied to various other contexts, where the material of interest is dangerous, impractical or costly. We propose four mixtures that could then be used to test the spectral response of any instrument, working at terahertz frequencies, without the need for an explosive substance.

Syntheses of ‘Hemtex’ Simulants of Energetic Materials and Millimetre Wave Characterisation Using the Teraview CW400 Spectrometer: Fundamental Studies for Detection Applications

“…The simulants were compared with Semtex as the threat material which varies from ~1.6 to 1.75 in refractive index according to the literature [9,10] possibly due to batch-to-batch variation. The Hemtex simulants ′ against frequency for 0%, 0.1%, 1% and 10% chlorobenzene in cyclohexane, respectively.…”

Recent Developments in Spectroscopic Techniques for the Detection of Explosives

“…Due to the importance of rapid, automatic, and non-contact detection of explosives for homeland security and environmental safety [8], a variety of spectroscopic technologies have been employed to detect trace quantities of explosives; for example, terahertz (THz) spectroscopy [9,10], laser induced breakdown spectroscopy (LIBS) [11,12,13,14,15,16], Raman spectroscopy [17,18,19,20,21,22], ion mobility spectrometry (IMS) [23,24,25,26], nuclear magnetic resonance (NMR) [27,28,29,30], nuclear quadrupole resonance (NQR) [31,32,33], laser-induced thermal emissions (LITE) [34,35], infrared (IR) spectroscopy [36,37,38], mass spectrometry [39,40,41,42,43,44,45,46], optical emission spectroscopy (OES) [47,48], photo-thermal infrared imaging spectroscopy (PT-IRIS) [49,50,51], photoacoustic techniques [52,53,54], FT-FIR spectroscopy [55], microwave [56], and millimeter-wave [57], etc. Various electromagnetic radiations such as X-ray [58] and γ rays [59] have also been employed in explosive detection.…”