Practical implementation of absorption spectroscopy technology in a device for detecting trace amounts of explosives on objects.
Boreysho Alexey Anatolyevich1, Candidate of Economic Sciences,
Strakhov Sergey Yuryevich1, Candidate of Physical and Mathematical Sciences
Konovalov Konstantin Anatolyevich1,
Romanov Alexander Yuryevich2,
Druzhinin Sergey Leonidovich1,
Perkhina Elena Viktorovna1
1 «NPP «Laser Systems»
2GU «NPO «Special Equipment and Communications» of the Ministry of Internal Affairs of Russia, tel./fax. +7 (495) 6733629
Practical implementation of absorption spectroscopy technology in a device for detecting trace amounts of explosives on objects
The work is devoted to the urgent problem of developing new effective means of counteracting terrorism, namely — a new device for detecting explosives. The work considers the practical implementation of the principle of absorption infrared spectroscopy of explosives and the method of attenuated total internal reflection within the framework of the Dannik-4 device for detecting trace amounts of explosives on the surfaces of objects. Such a device is unique and has no direct analogues; its advantages are short analysis time (1..3 s), fairly high sensitivity (0.1 -1 μg), ease of operation and maintenance, as well as — high speed of calibration and cleaning after detecting explosives.
As is known, all methods of detecting explosives (HE) can be divided into direct and trace. Direct methods are aimed at detecting HE in quantities of several tens of grams. Trace methods allow detecting small quantities of HE (traces) at a level of about 10-3-10-13 grams. Among the trace methods, the most common are electrochemical methods — ion mobility spectrometers, gas chromatographs, mass spectrometers, as well as — kits using color chemical reaction methods, etc. One of the areas of trace detection is the use of optical methods, in particular, absorption spectroscopy methods.
Absorption spectroscopy is based on the use of the effect of absorption by the substance under study of optical radiation with certain wavelengths that coincide with the absorption lines characteristic of each substance. Explosives have infrared (IR) absorption spectra concentrated in the range of 5-10 μm and caused by valence and deformation vibrations of the molecules in their composition [2, 3].
To implement absorption spectroscopy, the works [2, 3] proposed to use the attenuated total internal reflection (ATIR) method, the scheme of which is shown in Fig. 1. ATR is a phenomenon based on the penetration of a light wave from an optically denser medium 1 into a less dense medium 2 to a depth commensurate with the wavelength of the radiation. This effect is observed under conditions of total internal reflection. If medium 2 does not absorb radiation, then attenuation of total internal reflection does not occur, and all the radiation energy returns to medium 1. If, when radiation passes into medium 2, partial absorption of light occurs at wavelengths corresponding to the absorption spectrum of the medium, then the ATR effect occurs. Thus, the spectrum of the wave passing through the prism contains information about the absorption spectrum of medium 2 applied to the prism. In practice, medium 2 can be an object tested for the presence of explosives on it. The theory of the ATR method is described in detail in [1].
Fig. 1. Scheme of the ATVR method
A diffraction grating, a Fourier spectrometer, or a linear spectral filter can be used as a spectrum analyzer. The operating principle of a Fourier spectrometer and a diffraction grating is described in detail in numerous works, for example, in [4]. A linear spectral filter is an extended filter with alternating coatings, each section of which passes a certain spectral interval and is recorded by a separate receiver (or separate elements of a matrix receiver). The advantages and disadvantages of various spectrum analyzers are presented in Table 1.
Table 1. Comparison of spectrum analyzers
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