Transmission and Reflection Terahertz Spectroscopy of Insensitive Melt-Cast High-Explosive Materials

Abstract

Currently, artillery shells and grenades that are introduced into the market are based on melt-castable insensitive high explosives (IHEs), which do not explode while they run a risk of impact, heat or shrapnel. Particles of explosives (such as hexogen, nitroguanidine and nitrotriazolone) are suspended in different proportions in a matrix of 2.4-dinitroanisole. In this paper, we investigated samples of commonly used IHEs: PAX-41, IMX-104 and IMX-101, whose internal structures were determined by a scanning electron microscope. Terahertz time domain spectroscopy was applied in both transmission and reflection configurations. At first, the complex refraction indices of four pure constituents creating IHEs were determined and became the basis of further calculations. Next, the experimentally determined transmission and reflection spectra of IHEs and pure constituents were compared with theoretical considerations. The influence of the grain size of constituent material and scattering on the reflection spectra was analysed, and good agreement between the experimental and theoretical data was achieved.

Study of terahertz reflection spectra of optically thin RDX samples by terahertz imaging with spectral resolution

“…Small amounts of substance in the form of optically thin layers are of interest in the detection of explosives. In our experiments, we used samples with surface concentrations of 0.75 to 50 mg/cm2, for which the RDX layer thickness h did not exceed of the order of 100 μm, and the optical thickness α·h≲1, where α∼100 cm -1 3 , 9 , 12 , 13 is the absorption coefficient of RDX in the region of 0.8 THz. Under such conditions, it is necessary to take into account the reflection of THz radiation from the sample/substrate boundary.…”

“…At the moment, there are many works on the topic of THz spectroscopy of explosives devoted to the study of samples that have undergone preliminary preparation aimed at minimizing scattering effects—the particles of the analyzed substance are crushed, mixed with particles that form a neutral isotropic matrix (for example, with a powder of polyethylene particles) and then pressed into tablet 10 – 13 At the same time, in the literature, one can find works devoted to spectral studies of explosive samples in the presence of significant scattering (including using terahertz time-domain spectroscopy—THz-TDS, for example, Refs. 14–16).…”

Substance Detection and Identification Using Frequency Doubling of the THz Broadband Pulse

“…Terahertz time-domain spectroscopy (THz TDS) is a material analysis method which is currently widely applied for both basic research and security problems, as well as for industrial applications. It is well known that THz TDS is used for the detection and identification of explosives and dangerous substances [1][2][3][4][5][6][7][8]. It is currently considered as a powerful new tool for research in the chemical sciences and molecular structure investigations [9][10][11], biomedical and pharmaceutical applications [12,13], non-destructive control [14][15][16], and quality control in the agri-food industry [17][18][19].…”

Titanium-Based Microbolometers: Control of Spatial Profile of Terahertz Emission in Weak Power Sources

“…Because of non-ionizing nature of THz radiation, imaging in this range can be found as a beneficial tool for medicine and biomedical stuff inspection [2][3][4]. As THz frequencies display the ability to propagate in dielectric medium without strong attenuation, THz imaging and spectroscopy can also serve as valuable instruments for security needs [5][6][7], post packages inspection [8][9][10] or industrial materials control and their identification [11][12][13][14]. However, direct implementation of THz technology still meets severe difficulties related mainly to reliability of active components (emitters and detectors) and issues of precise alignment of the optical system due to the presence, as a rule, of passive bulky optical elements like mirrors, lenses or beam splitters.…”