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1.
核四极共振隐藏炸药探测信息库设计 总被引:1,自引:0,他引:1
利用核四极共振(Nuclear Quadrupole Resonance, 简称NQR)技术探测炸药时,实验复杂,参数繁多. 原子核参数、脉冲参数、环境参数等各参数对炸药共振频率及探测信噪比都有不同程度的影响. 针对长期以来国内外一直没有统一的炸药信息库,测试数据无法有效记录和管理的现象,在全面分析各参数与共振频率之间关系的基础上,设计并实现了隐藏炸药探测信息库. 该信息库能有效的收集和记录炸药参数信息,为今后炸药测试数据的统计分析提供统一规范的数据支持. 相似文献
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D. Ya. Osokin R. R. Khusnutdinov G. V. Mozzhukhin B. Z. Rameev 《Technical Physics》2014,59(5):749-753
The application of the multipulse sequences in nuclear quadrupole resonance (NQR) detection of explosive and narcotic substances has been studied. Various approaches to increase the signal to noise ratio (SNR) of signal detection are considered. We discussed two modifications of the phase-alternated multiple-pulse sequence (PAMS): the 180° pulse sequence with a preparatory pulse and the 90° pulse sequence. The advantages of optimal filtering to detect NQR in the case of the coherent steady-state precession have been analyzed. It has been shown that this technique is effective in filtering high-frequency and low-frequency noise and increasing the reliability of NQR detection. Our analysis also shows the PAMS with 180° pulses is more effective than PSL sequence from point of view of the application of optimal filtering procedure to the steady-state NQR signal. 相似文献
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A J Blauch J L Schiano M D Ginsberg 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,139(1):139-151
The low signal-to-noise ratio (SNR) of nuclear quadrupolar resonance measurements has motivated research on signal enhancement methods, including multipulse sequences that facilitate signal averaging, the development of interlaced pulse sequences, and super-Q coils. More recently, it has been shown that feedback can be used to automatically optimize pulse sequence parameters, maximizing the SNR. This paper extends this work by using feedback to optimize the offset frequency in the strong off-resonant comb pulse sequence. Analysis and results are presented for a sample of sodium nitrite at both liquid nitrogen and room temperatures. 相似文献
4.
利用核四极矩共振技术探测炸药 总被引:1,自引:0,他引:1
介绍了用核四极矩共振的原理进行爆炸危险物品检测的方法及实验测试系统. 该系统运用特殊的激励信号来激发被检测样品中所含的特殊元素14N(炸药的主要成分),使其产生核四极矩共振,并产生辐射,从而达到检测的目的. 由于该辐射信号的能量非常小(10 nV量级),在通常的环境中很难检测该信号, 这就对此弱信号的检测和提取提出了很高的要求. 本测试系统使用了一系列有效的组合激励信号及弱信号采集、处理技术,在通常环境中成功地检测到了RDX(黑索金)信号. 相似文献
5.
For reliable detection of explosives, a combination of methods integrated within a single measurement platform may increase detection performance. However, the efficient field testing of such measurement platforms requires the use of inexplosive simulants that are detectable by a wide range of methods. Physical parameters such as simulant density, elemental composition and crystalline structure must closely match those of the target explosive. The highly discriminating bulk detection characteristics of nuclear quadrupole resonance (NQR) especially constrain simulant design. This paper describes the development of an inexplosive RDX simulant suited to a wide range of measurement methods, including NQR. Measurements are presented that confirm an RDX NQR response from the simulant. The potential use of the simulant for field testing a prototype handheld NQR-based RDX detector is analyzed. Only modest changes in prototype operation during field testing would be required to account for the use of simulant rather than real explosive. 相似文献
6.
Three-Frequency Composite Multipulse Nuclear Quadrupole Resonance Technique for Explosive Detection 总被引:1,自引:0,他引:1
G. V. Mozzhukhin B. Z. Rameev R. R. Khusnutdinov N. Do?an B. Aktas 《Applied magnetic resonance》2012,43(4):547-556
New method of multifrequency nuclear quadrupole resonance (NQR) for the explosive detection has been proposed. This technique consists of application of the series of composite excitation circles, each consisting of two or three successive pulses of different frequencies. In this work, we study in detail the multipulse sequence consisting of n excitation sets, each set consists of three pulses. The first pulse is applied with frequency ?? ?, the second pulse with frequency ?? 0, and the third pulse with frequency ?? ?C, but with a shifted phase. The NQR signal is detected at the frequency ?? +. The maximal amplitude of the detected signal is obtained by tuning the pulse parameters at frequencies ?? ? and ?? 0. We have shown that the phase of the NQR signal at the frequency ?? + second part of the composite pulse with the frequency ?? 0 the signals with different phases to suppress the spurious signals. The method could be used for increasing the NQR signal, avoiding the spurious signals and improving the reliability of NQR detection. Possible applications of the method for the explosive detection are also discussed. 相似文献
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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%. 相似文献
9.
在核四极矩共振(NQR)领域,射频激励脉冲信号的优劣对NQR响应信号有重要影响.针对常规方法中射频激励脉冲参数不可控的问题,本文基于32位闪存微型控制器STM32和直接数字频率合成(DDS)芯片AD9910设计了一种相位可控激励脉冲发生器.采用STM32控制AD9910产生波形参数(脉冲宽度、脉冲间隔、脉冲个数和共振频率等)可控的射频激励脉冲,利用LabVIEW软件平台设计脉冲参数设置界面,并建立计算机与微控制器通信,实现波形参数的精确优化控制.实验结果表明,该方法实现了相位可控的NQR激励脉冲序列,可为后续NQR信号检测提供有效激励源. 相似文献
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T. N. Rudakov V. T. Mikhaltsevitch J. H. Flexman P. A. Hayes W. P. Chisholm 《Applied magnetic resonance》2004,25(3-4):467-474
Modification of the steady-state free precession (SSFP) multipulse technique for the effective detection of nuclear quadrupole resonance (NQR) signals was studied. This modification is based on the use of the preparatory pulse in the SSFP pulse sequences. It was shown that under certain conditions the total intensity of accumulated NQR signal can be increased. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of sodium nitrite (NaNO2) are presented and convincingly demonstrate the technique’s effectiveness. 相似文献
12.
Samanwita Pal 《Molecular physics》2013,111(6):759-767
Recent work on the nuclear quadrupole resonance (NQR) investigation of molecular dynamics in the solid state has relied on 2D methods. We report our studies of dynamic processes by 1D shaped pulse NQR spectroscopy. Significant advantages include considerably shorter experimental duration, clear definition of the exchange time window, and avoidance of off-resonance effects. The reorientation of the Cl3C? group in polycrystalline chloral hydrate [Cl3C–CH(OH)2] is considered as a test case. This may be modelled as a three-site exchange process. An analysis of the generalised Bloch–McConnell equation is performed to formulate the kinetic matrix. The present approach involves simultaneous excitation of the sites that undergo chemical exchange by employing a suitably modulated shaped RF pulse, followed by a mixing time, and finally a suitable read pulse for signal detection. The experimental signal intensities are plotted against the mixing time to extract the kinetic parameters, i.e. the exchange rate and the spin-lattice relaxation rate. Variable temperature measurements are carried out to determine the activation parameters. Short experiment times are possible in our 1D mode, enabling a large number of runs to be readily performed as a function of mixing time and temperature. The kinetic and activation parameters obtained in the case of chloral hydrate are in good agreement with recent literature values. 相似文献
13.
Mikhaltsevitch VT Rudakov TN Flexman JH Hayes PA Chisholm WP 《Solid state nuclear magnetic resonance》2004,25(1-3):61-63
Experimental results of comparing composite pulses in nitrogen-14 NQR, that are analogous to common 90 degrees RF pulses in powder, are presented. All tested pulses have been taken from publications in journals. Comparative diagrams of the measurement results for induction signals and echo signals are presented. The results of the measurements demonstrate that the best outcomes are achieved when the composite pulse (45)0(95)180(164)0 is used. 相似文献
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Experiments on detecting induction signals of nuclear quadrupole resonance (NQR) on 14N nuclei in hexahydro-1,3,5-trinitro-s-triazine C3H6N6O6 (RDX) with preliminary changed population densities of NQR energy levels upon exposure to a saturating pulse are described. It is demonstrated that this actually causes the induction signal amplitude to change; however, complete saturation of the transition cannot be reached because of the NQR relaxation time. It is also demonstrated that the results of calculations without regard for the relaxation processes in RDX lack experimental support. Experimental data demonstrate the feasibility of application of the methods of preliminary change of the population densities (by pumping) for multifrequency experiments in NQR and explosive detection.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 49–52, April, 2005. 相似文献
16.
Theoretical and experimental results are presented for the case of Zeeman perturbed nuclear quadrupole resonance (NQR) using spin-3/2 nuclei with a small Zeeman interaction, gammaB0, while the sample is very slowly rotated. It is found that the decay envelope for a simple two-pulse echo measurement can be strongly affected even though the sample may rotate only a few degrees or less during the course of the measurement. To lowest order the decay envelope can be described using a one dimensional function of the product of gammaB0, the rotation rate, and the square of the pulse spacing. Aside from an indirect and weak dependence on the quadrupole asymmetry parameter, eta, the result is independent of the NQR frequency. Identical results are expected for a stationary sample in a small rotating magnetic field. The effect seen here may be used to advantage to measure rotational motion, for example of particles in fluids, or may be an additional complication for some Zeeman perturbed NQR measurements, including some NQR detection and imaging methods. 相似文献
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Pure nuclear quadrupole resonance (NQR) was combined with a rotating-frame imaging technique (rho NQRI). The method is suitable for powdery or crystalline materials containing quadrupole nuclei. The spatial information is encoded in the amplitudes of the free-induction decays (FIDs) by gradients of the radio frequency amplitude of the excitation pulse. The pulse length is incremented in a series of experiments so that a pseudo-FID can be formed from the intensities of a selected NQR line. A deconvolution procedure is used for the analysis of the pseudo-FIDs. The result is a sample profile along the gradient direction. The technique is particularly suitable for the detection of the spatial distribution of physical parameters producing NQR line shifts. Examples are stress or temperature. Two-dimensional images can be produced by rotating the sample step by step. For each orientation a profile across the sample is evaluated. A backprojection reconstruction formalism then permits the rendering of two-dimensional NQR images. 相似文献
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The off-resonance dependence of the amplitudes of the six dominant 14N nuclear quadrupole resonance (NQR) lines in commercial polymorphic trinitrotoluene (TNT) sample were experimentally determined for a wide range of experimental parameters when irradiated with the spin-lock spin-echo (SLSE) pulse sequence. We find that the amplitudes off-resonance dependence follows a sinc-like function with an additional modulation due to the spacing between the RF pulses. This dependence can be very well modeled with expressions we have derived for a single site 14N NQR in paranitrotoluene (PNT). The results can be immediately used for the reduction of the number of free parameters used in the robust signal processing models for the TNT NQR detectors. 相似文献
19.
The intensities of 14
N NQR signals have been calculated in relation to the amplitude of the initiating radiofrequency (RF) field of the radiopulse, the pulse duration, and the detuning. It is discussed whether it is possible to compensate the decrease in intensity of signals from some regions of an explosive which is in a nonuniform RF field by varying the detuning and the duration of the initiating pulse.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 105–107, October, 2004. 相似文献
20.
Rudakov TN Mikhaltsevitch VT Flexman JH 《Solid state nuclear magnetic resonance》2004,25(1-3):112-118
The behaviour of the magnetisation in the spin-1 system with the axial symmetry of the electric field gradient (EFG) tensor was analysed theoretically. The behaviour of the NQR signals in hexamethylenetetramine (C6H12N4) was also studied experimentally using the pulse NQR technique and sensitive equipment. It was shown that the axial symmetry of the EFG in a sample could not be the reason why spin-echo signals were not observed in conventional pulse experiments for the same type of sample. A very short spin-spin relaxation time T2 seems to be the reason of that. The signal-to-noise ratio was sufficient for measuring T2 in C6H12N4, which had not been reported earlier. Experimental results of applying certain pulse sequences to the 14N NQR in a sample are also presented. 相似文献