Pulsed spectrometer for nuclear quadrupole resonance for remote detection of nitrogen in explosives
ABSTRACT We describe a pulsed spectrometer for detection of nuclear quadrupole resonance on the nuclei of nitrogen N-14 with fast Fourier transform. The use of a multipulse sequence, four channel system for data registration and processing permits detection of the nuclear quadrupole resonance (NQR) signal in the presence of strong interference and the piezo effect. Using this spectrometer we registered the NQR signal from an explosive sample of 150 g (92% RDX) at a distance of 22 cm, and the time of detection was 81 s. © 2000 American Institute of Physics.
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ABSTRACT: With the global surge of terrorism and the increased use of bombs in terrorist attacks, national defence and security depart- ments now demand techniques for quick and reliable analysis, in particular, for detection of toxic and explosive substances. One approach is to separate different analytes and matrix material before detection. In this work microliquid chromatography was used to separate two dinitrotoluene (DNT) isomers prior to detection via online UV–Vis spectroscopy. For identification, retention times were compared with reference samples and quantification was done by integration of UV–Vis absorption. Because UV detection is not particularly selective, Raman microscopic analysis was coupled to the liquid chromatography using a flow-through microdispenser. Because DNT is difficult to detect with conventional Raman spectroscopy, the sensitivity was increased via surface-enhanced Raman scattering (SERS) using silver-quantum dots. Different analytical approaches to identify and quantify mixtures of two DNT isomers were evaluated. Good quantitative results were obtained using UV detec- tion after microchromatographic separation (Limit of Detection: 0.11 and 0.06 for 2,4-DNT and 2,6-DNT). Coupling with SERS allowed for more confident differentiation between the highly structurally similar DNT isomers because of the additional spectral information provided by SERS. The application of a partial least squares algorithm also allowed direct SERS detection of DNT mixtures (root mean square error of prediction: 0.82 and 0.79mg/L for 2,4-DNT and 2,6-DNT), circumventing the time-consuming separation step completely.Journal of Raman Spectroscopy 08/2012; 43(8):998-1002. · 2.68 Impact Factor
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ABSTRACT: Principles of message transfer in telecommunication systems are considered when a wide transmission band is required, which can result in tuning away from the transmitting station if the signal-to-noise ratio (SNR) is insufficiently high. Based on a solution of the Fokker-Planck-Kolmogorov equation, it is demonstrated that a signal below noise is broadened 20 times for SNR = 0.05. This makes signal accumulation difficult. The matrix pencil method of information theory is used to demonstrate that the broadening of a signal below noise and shift of its frequency detuning interfere with reliable signal detection for SNR ≤ 0.05. An analog of the Bohr complementarity principle is used to analyze the NQR detector. In addition, performance of the NQR-mine detector used to clear of mines territories of former military actions is examined.Russian Physics Journal 01/2005; 48(2):148-155. · 0.41 Impact Factor
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ABSTRACT: The spectral estimation in local nuclear quadrupole resonance at a high noise level is performed for the first time using the modern techniques of linear prediction (LPSVD) and matrix pencil (ITMPM). The fast Fourier transform with signal accumulation does not ensure the required sensitivity in the case of weak signals when the object and the receiver of the spectrometer are spaced widely apart or when there is an effect of adverse factors (screening, interference, random disturbance, etc.), which is typical of remote monitoring in actual practice. It is demonstrated that the use of the proposed techniques considerably increases the efficiency of spectral estimation in this field of solid-state spectroscopy and, in particular, avoids the phase errors arising in usual experiments at a signal-to-noise ratio of less than 0.5.Optics and Spectroscopy 10/2002; 93(4). · 0.56 Impact Factor