Remote Detection Of Explosives Research Articles

INVESTIGATION ABOUT ELECTROMAGNETIC FIELD TOPOLOGY OF THE SPIRAL COIL FOR NQR DETECTOR OF EXPLOSIVE AND NARCOTIC SUBSTANCES

Given the increased likelihood of dangerous situations in Ukraine and abroad related to the intensification and scale of terrorist acts, it is important not only to quickly locate and eliminate the terrible consequences, but also to prevent, including prevent destabilizing factors. That is why remote detection of explosives and drugs is relevant and promising in the direction of strengthening the fight against terrorism and increasing national security. A promising method for detecting the vast majority of explosives and narcotics that contain nitrogen (14N) or chlorine atoms (35Cl, 37Cl) is the nuclear quadrupole resonance method. In the presence of a gradient of high-frequency field strength inside the sample in the process of forming the response signal is “blurring” the vector of the total spin magnetization, which leads to the expansion of the resonant signal and reduce its amplitude. Increasing the homogeneity of the high-frequency field is especially important for the detection of weak signals observed in the study of substances with a low natural prevalence of magnetoactive nuclei. The paper presents the results of research on the topology of the electromagnetic field strength of a helical coil designed for use as a transmitting and receiving antenna of a portable detector of explosives and drugs, the principle of which is based on the registration of 14N isotope signals by nuclear quadrupole resonance. To determine the topology of the electromagnetic field, a computational domain was created, which is a model of the physical structure of the spiral coil. The finite element method performed numerical simulations in COMSOL Multiphysics. The simulation was performed at a frequency of 3.4 MHz, which is close to the value of the detection frequency of the attenuation signal of free induction from sodium nitrite 3.41 MHz. The best results were shown by the model of the coil with five turns, internal radius of 25 mm, external radius of 225 mm. The obtained magnetic field diagrams indicate better resistance to radio frequency interference when working in a real experiment. Based on the data obtained during the simulation, a multilayer (Multislice) model of the electric field and the isosurface of the electromagnetic field of the studied model were created, which demonstrate the dynamics and density of the electromagnetic field around the coil. From the obtained graphical dependences it is possible to draw a conclusion about the normalized attenuation of the intensity of electric field radiation from the geometric center of the coil, which, in turn, makes it clear exactly how to place the sample.

Molecularly Imprinted Silver Nanocomposites for Explosive Taggant Sensing

Sensing explosive taggants such as 3-nitrotoluene (3-NT) and 2,3-dimethyl-2,3-dinitrobutane has become a strategic priority in homeland security. This work reports the synthesis of a solid-state plasmonic sensor based on a nanocomposite of Ag nanoparticles (NPs) embedded in a molecularly imprinted polymer (MIP) for selective detection of 3-NT, an explosive taggant for 2,4,6-trinitrotoluene. In our approach, the in situ synthesis of Ag NPs and the molecular imprinting with 3-NT as a template take place simultaneously inside the polyethyleneimine (PEI) thin film during the baking step after spin coating. The MIP sensor fabrication is done by a low-cost, fast, and scalable one-step procedure. We demonstrate the chemosensing capabilities of Ag-PEI MIP nanocomposites to 3-NT using the localized surface plasmon resonance band intensity decay as a sensing parameter. The molecular imprinting approach results in an enhancement of specific sensor response to 3-NT, with a limit of detection of 54.8 ng for 3-NT and a sensitivity of 24.0% ± 3.0%. We tested the MIP sensor specificity by comparing the sensor response to several NO2-containing molecules. The Ag-PEI MIP sensor demonstrated a robust, specific molecular recognition toward 3-NT. Because the MIP nanocomposite sensor is easy to prepare, easy to use, and inexpensive, these plasmonic sensors can be easily implemented with portable reading platforms into remote explosive detection and bomb disposal robots.

Development of a cost-effective remote explosives detection system based on Raman spectroscopy

Near real-time detection and identification of explosives from safe distances remains a challenging defense technology that requires both scientific and engineering perspectives in the design and development. Here, we demonstrated a cost-effective standoff Raman system for detecting explosive materials from distances up to 30 m. The optical system consists of an 8-inch Schmidt–Cassegrain telescope for Raman scattering light collection, while a compact grism was used to generate Raman spectrogram. An image intensifier from night vision technology was incorporated for amplifying the extremely weak Raman spectrum to a level detectable by a thermoelectric-cooled CMOS camera. A nanosecond pulsed laser at 440 nm with peak power of 0.41 MW was used as an excitation source, and the standoff Raman measurement was performed for test samples, including Ba(NO3)2, BaSO4 and NaNO3 powders. The spectral resolution and signal-to-noise ratio performance of the system were evaluated for the samples placed at distances of 10, 20 and 30 m. It was found that the standoff Raman system can resolve such Raman spectra, showing clear characteristic peaks of Ba(NO3)2, BaSO4 and NaNO3 at 1,045.9, 986.4 and 1,066.5 cm−1, respectively. These spectrum results agree well with the Raman spectra obtained from a standard close-range Raman system.

Study of the possibility of increasing the accuracy of measuring the concentration of particles of explosives by remote sensing methods

Most of the existing methods for detection of explosives require sampling and sample preparation, whereas in the search for explosives, it is not always possible to contact the explosive device (ED). In this connection, the methods for remote detection of explosives by detecting their particles present in various quantities near or on the surface of the explosive are of particular interest. The difficulty of detecting such substances lies in the fact that, in addition to full-scale samples, they may be in the package. In addition, it often becomes necessary to detect a trace amount of hazardous substances on packages and contact surfaces. The purpose of the article is to study the possibility of improving the accuracy of lidar measurements of the concentration of particles of explosives, taking into account the width of the laser emission line and the absorption width of the molecule under study.

Remote detection of explosives using field asymmetric ion mobility spectrometer installed on multicopter.

The detection of explosives and drugs in hard-to-reach places is a considerable challenge. We report the development and initial experimental characterization of the air analysis system that includes Field Asymmetric Ion Mobility Spectrometer, array of the semiconductor gas sensors and is installed on multicopter. The system was developed based on the commercially available DJI Matrix 100 platform. For data collection and communication with operator, the special compact computer (Intel Compute Stick) was installed onboard. The total weight of the system was 3.3kg. The system allows the 15-minute flight and provides the remote access to the obtained data. The developed system can be effectively used for the detection of impurities in the air, ecology monitoring, detection of chemical warfare agents, and explosives, what is especially important in light of recent terroristic attacks. The capabilities of the system were tested on the several explosives such as trinitrotoluene and nitro powder.

Multidetector system for nanosecond tagged neutron technology based on hardware selection of events

At the T(d, n)He4 reaction a neutron is accompanied by an associated alpha-particle emitted in the opposite direction. A time and a direction of the neutron escape can be determined by measuring a time and coordinates of the alpha particle at the position-sensitive alpha-detector. The nanosecond tagged neutron technology (NTNT) based on this principle has great potentialities for various applications, e.g., for remote detection of explosives. A spectrum of gamma-rays emitted at the interaction of tagged neutrons with nuclei of chemical elements allows identify a chemical composition of an irradiated object. For practical realization of NTNT, a time resolution of recording the alpha-gamma coincidences should be close to 1 ns. The total intensity of signals can exceed 1 × 106 1/s from all gamma-detectors and 7 × 106 1/s from the alpha-detector. The processing of such stream of data without losses and distortion of information is one of challenging problems of NTNT. Several models of analog DAQ system based on hardware selection of events were devised and their characteristics are examined. The comparison with the digital DAQ systems demonstrated that the analog DAQ provides better timing parameters, lower power consumption, and higher maximum rate of useful events.

Remote Explosives Detection (RED) by Infrared Photothermal Imaging

ABSTRACTRED is a technique we have developed for stand-off detection of trace explosives using infrared (IR) photo-thermal imaging [1,2,3]. RED incorporates compact IR quantum cascade lasers tuned to strong characteristic absorption bands and may be used to illuminate explosives present as particles on a surface. An IR focal plane array is used to image the surface and detect any small increase in the thermal emission upon laser illumination. We have previously demonstrated the technique at several meters to 10’s of meters of stand-off distance indoors and in field tests [4,5], while operating the lasers below the eye-safe intensity limit (100 mWcm2) [6]. Sensitivity to traces of explosives as small as a nanogram has been demonstrated. By varying the incident wavelength slightly, we can readily show selectivity between individual explosives such as TNT and RDX. Using a sequence of lasers at different wavelengths, we increase both sensitivity and selectivity. A complete detection protocol can be performed in a sub-second time domain. More recently, RED has been used to emphasize measurements with cooled detectors in addition to examining the utility of filtering the collected thermal emission signal which is rich in analyte-specific spectroscopic information. A next generation RED system and detection algorithm is being developed to take advantage of these more powerful features. This manuscript will include an overview of the approach and recent experimental results.

A two-frequency coherent pulse NQR spectrometer

A two-frequency coherent pulse spectrometer has been designed for seeking and recording nuclear quadrupole resonance spectra and studying coherence transfer processes, quasi-stationary states, and transient processes in multipulse sequences. The functional diagram of this spectrometer can be used in production of equipment for remote detection of explosives and drugs, which will require only an increase in the output power of the transmitter.

Detection of condensed-phase explosives via laser-induced vaporization, photodissociation, and resonant excitation

We investigate the remote detection of explosives via a technique that vaporizes and photodissociates the condensed-phase material and detects the resulting vibrationally excited NO fragments via laser-induced fluorescence. The technique utilizes a single 7 ns pulse of a tunable laser near 236.2 nm to perform these multiple processes. The resulting blue-shifted fluorescence (226 nm) is detected using a photomultiplier and narrowband filter that strongly block the scatter of the pump laser off the solid media while passing the shorter wavelength photons. Various nitro-bearing compounds, including 2,6-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) were detected with a signal-to-noise of 25 dB. The effects of laser fluence, wavelength, and sample morphology were examined.

Absolute Raman cross-sections of some explosives: Trend to UV

The Raman cross-section dependence on excitation energy in spectral range 620–248 nm have been investigated for UN, TATP, RDX, TNT, and PETN explosives. For all investigated explosive materials, significant pre-resonance enhancement in the UV spectral range has been revealed. Normalized Raman scattering signals are 100–200 times stronger with UV excitation at 248 nm compared to visible excitation at 532 nm. Thus the gated Raman technique with UV excitation has significant advantages compared to IR–VIS excitation for the remote detection of explosives. Certain of the observed Raman lines exhibit deviations from classical λ −4 dependence of Raman cross-section and may totally disappear with UV excitation. The possible explanation for this may be that numerous electronic transitions contribute to the molecular polarizability. These contributions could be of opposite sign and lead to partial cancellation of certain transitions. Another possible reason could be that this is a result of the stronger UV absorption that reduces the sampling volume and therefore the number of scatterers that produce the Raman signal.

Pulsed laser surface fragmentation and mid-infrared laser spectroscopy for remote detection of explosives

Stand-off technology for the remote detection of explosives and their traces on contaminated surfaces is a field of research that has recently gained much interest. Optical methods are well established in applications for counterterrorism because they facilitate analysis without contact between human being and hazardous materials. In this paper, to our knowledge for the first time, a remote stand-off detection system is developed by combination of pulsed laser fragmentation and pulsed mid-infrared laser absorption spectroscopy. Since the absorption of explosives is more efficient for infrared wavelengths laser radiation in the eye safe region around λ=1.47 μm rather than the conventional Nd:YAG laser line at λ=1.06 μm is preferred for the fragmentation. Generated product gases such as nitric oxide are probed by a synchronized distributed feedback quantum cascade laser (DFB-QCL) at λ≈5.3 μm. The ratio of NO and NO2 is a measure to distinguish between energetic and non-energetic materials.

Laser-induced plasma spectroscopy for mine detection and verification

Laser-induced breakdown spectroscopy (LIBS) in combination with a conventional mine prodder is applied for remote detection of explosives and mine housing materials. High power subnanosecond laser pulses (pulse powerEp= 0.6 mJ and pulse duration Δt= 650 ps) at 1064 nm with a typical repetition rate of 10 kHz are generated by using a passively Q-switched Cr4+:Nd3+:YAG microchip-laser as seed-laser for an Yb-fiber amplifier. In the present investigation, the ratios of “late” and “early” LIBS intensities for the cyanide (CN) plasma emission at 388 nm and for the C-emission at 248 nm are used for data analysis. This allows the classification of different explosives and mine casing materials under real time conditions and also similar applications to materials processing.

Terahertz imaging using an interferometric array

Most methods of imaging in the terahertz (THz) spectral region utilize either pulsed-laser sources or require the THz generation and detection sources to be phase coherent. The application of interferometric imaging to the THz range is described. Interferometric imaging offers considerable advantages in this regard due to its ability to image with only a handful of detector elements, image many sources of THz radiation at once, image incoherent as well as coherent sources, and provide spectral information as well as spatial imaging information. The THz interferometric imaging method is potentially useful for remote detection of explosives.

Application of a unique scheme for remote detection of explosives

We report on an application for remote detection of explosives containing nitro groups. This is a step forward in implementing a unique scheme introduced recently as a remote, real-time, detection tool. The scheme is applied to a system for 2,4,6-trinitrotoluene (TNT) vapor detection. The sensitivity of our systems is better than 15 parts per billion (ppb) for near ambient conditions (i.e. atmospheric pressure and explosive sample holder at temperature of 28 °C) and at a range of 2.5 m. The response time of the system is about 15 s.

Photodissociation followed by laser-induced fluorescence at atmospheric pressure and 24 °C: a unique scheme for remote detection of explosives

A unique scheme has been applied for sensitive remote detection of 2,4,6-trinitrotoluene (TNT) vapor trace amounts at atmospheric pressure and 24 degrees C. The detection concept is based on a single laser beam inducing a tandem process: photodissociation of TNT vapor followed by highly selective detection of its photofragments vibrationally excited NO, utilizing laser-induced fluorescence with the A2Sigma+(v' = 0) <-- X2Pi(v'' = 2) transition. A detection sensitivity of at least 8 parts in 10(9) of TNT vapor with a signal-to-noise ratio of approximately 10 has been experimentally verified for an unfocused approximately 5-mJ laser beam, measured at a distance of approximately 15 cm from the TNT sample.

Remote sensing by nuclear quadrupole resonance

Detection of explosives has the flavor of those mathematical problems that are not invertible. It is easier to hide explosives than to find them. Many approaches have been proposed and executed for the remote detection of explosives, contraband materials, weapons of mass destruction, currency, etc. Most detection technologies suffer from a common problem: the features they look for, such as discontinuities in electrical conductivity, are not properties of the target but are contained, to some degree, in the more benign surroundings. Such a degeneracy leads to in the response. For example, resolving the false alarms generated by this clutter can determine the rate of advance of a conventional electromagnetic metal detector employed as a landmine detector. One approach that provides a unique signature is nuclear quadrupole resonance (NQR) (the technique is also called QR, to avoid confusion with strictly nuclear techniques). This paper outlines the important physical principles behind the use of NQR for remote detection, indicates areas of applicability, and presents results of field trials of a prototype landmine detection system.

AOTF Raman spectrometer for remote detection of explosives

A spectrometer based on acousto-optic tunable filters is developed for use in measuring Raman spectra as part of a detection system that is low-cost, reliable, and field-portable. The system is coupled with a fiber optic bundle to carry the excitation laser light to the sample and to collect the Raman scattered light. Spectra of the explosives trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX) and nitroguanidine (NQ) were obtained in very short times and are in good agreement with those taken with conventional Fourier transform Raman spectrometers. Spectra of mixtures of explosives were also obtained and show no overlap of their characteristic Raman bands.