Detection of explosives in situ is of major importance in several applications: finding hidden explosives in airport luggage and in mail; screening of personnel for concealed explosives; environmental monitoring of explosives-contaminated sites; and, detection of buried landmines. Mobile and hand-held detectors have been developed for the various applications. They can be sub-divided into three classes: vapor and particle detectors; radiation detectors; and, biochemical detectors. An overview of the various explosives detectors and their principles of operation is presented.

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Field detection and monitoring of explosives

Publisher Summary This chapter gives the account of the detection of explosive devices. The detection can be classified into two schemes — ”seeing” the device and detecting a certain component which is common to all devices. X-ray imaging is a model example of the previous scheme. It gives an image of the contents of anitem under inspection. It is presented upon the operator to be acquainted with the explosive device. Metal detection is a very good example of the latter scheme. Almost all land mines contain no less than a little quantity of metal that can be detected through a metal detector. Evidently, many guiltless objects contain metal. The problem is separating the guiltless from the hazardous. To detect the explosive device without any hesitation is to detect it with the help of devices. The thermal neutron analysis and dual-energy X-ray give the specificity and issues of radiation, which can be challenging in some situations. This chapter discusses the nuclear quadrupole resonance (NQR). NQR stimulates and detects the radio frequency (RF) signals from certain nuclei in molecules of interest and are called explosives.

Nuclear Quadrupole Resonance Detection of Explosives

A sensor for detecting and differentiating chemical analytes includes a microscale body having a first end and a second end and a surface between the ends for adsorbing a chemical analyte. The surface includes at least one conductive heating track for heating the chemical analyte and also a conductive response track, which is electrically isolated from the heating track, for producing a thermal response signal from the chemical analyte. The heating track is electrically connected with a voltage source and the response track is electrically connected with a signal recorder. The microscale body is restrained at the first end and the second end and is substantially isolated from its surroundings therebetween, thus having a bridge configuration.

Sensor for detecting and differentiating chemical analytes

Publisher Summary Prevention of explosions requires the detection of bombs, bomb makers, and bomb placers State-sponsored actors and non-state-sponsored terrorists are the main threats on which explosives detection needs to focus The geographical location such as an airport or a building, whether the threat is on (or in) people or objects, the target mobility, and whether the target is moveable or fixed are all factors that impose constraints on the detection techniques employed and influence the operational deployment of bomb detectors In modern times, many techniques have been investigated for the detection of explosives and illicit chemicals Imaging techniques such as radiography are quite good for recognizing bombs either visually or by computer-aided image recognition, but as they are not particularly sensitive, they detect suspect items of a certain minimum size Detection of explosives is divided into bulk and trace technologies where the bulk detection looks for a mass with certain properties considered indicative of an explosive In detecting the presence of an explosive compound at trace levels, the general approach is to look for a specific chemical from a library of target compounds rather than for a general property To date, only two technologies have reached the original goal of certification, namely, X-ray computer tomography (CT) in 1996 and X-ray powder diffraction coherent Compton scattering in 2004

The Detection Problem

Comparative experimental analysis of composite pulses in 14N NQR

Nuclear quadrupole resonance (NQR) of14N nuclei has many advantages as a method for detecting nitrogen-containing explosives, the most important are very high chemical specificity, true noninvasive operation and detection of bulk explosive in situ only (no vapor or particular capture needed). One of the most high explosives is hexogen (RDX) often used by terrorists in plasticized forms. The ring nitrogen nuclei in an RDX molecule generate three sets of NQR frequencies corresponding to three physically nonequivalent positions of the molecule in the crystal lattice. The prototype device we have constructed is intended for inspection of suitcases for the presence of plastic explosives containing RDX or octogen by14N quadrupole resonance. It is essentially a fully automated PC-controlled pulsed FT NQR spectrometer equipped with a large volume (70 1) radio-frequency (RF) sample coil to accommodate a typical suitcase. The device consists of a measure chamber with an RF coil, tuning and matching box, an RF pulse transmitter and a control PC with dedicated cards like digital receiver, frequency synthesizer, pulse programmer and probe-tuning controller. The control software finds the NQR lines and measures their frequencies. An alarm is produced if any of these frequencies matches the characteristic NQR frequency of the explosive and the signal-tonoise ratio exceeds the preset threshold. Multipulse sequences of the type SORC (strong off-resonance comb) or SLSE (spin-locked spin echo) were used in order to increase the allowed data acquisition rate. We could detect 230 g of PMW-8, a plastic explosive (containing 81% of RDX) in 10 s or 100 g in 30 s. Detection probability was not less than 90%.

B. Nogaj

Papers

Detection of plastic explosives in luggage with14N nuclear quadrupole resonance spectroscopy