核四极共振隐藏炸药探测信息库设计

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.      

Pulsed 14N NQR Device Designed to Detect Substances in the Presence of Environmental Noise

A new device designed for both volumetric and surface NQR detection of substances spatially located in several positions, and in the presence of environmental interference, is described. The device consists of two probe coils, placed on the same detection plane, for excitation and detection of NQR signals. Experimental results obtained using Strong Off Resonance Comb (SORC) pulse sequences, for the excitation of the ν- transition in samples of Sodium Nitrite (NaNO ₂), are presented. It is shown that, when the total signals induced in each coil are properly combined, the interference commonly detected in both coils is attenuated relative to the NQR signal detected by either one or both probe coils. NQR signal can be detected by either one or both coils, but in both cases the noise induced by distant environmental sources is attenuated. These files correspond to the revised version of the paper N° O-G-6, entitled “Pulsed ¹⁴N NQR device designed to detect substances in the presence of environmental noise” presented at the XVII International symposium on Nuclear Quadrupole Interactions, held in Bonn, Germany in 2004. Argentinian and International patents pending.     

PETN炸药NQR信号处理方法

利用核四极共振(Nuclear Quadrupole Resonance, NQR)原理探测隐藏炸药,具有准确率高、误报率低、无放射性沾染和防护问题等优点. 但NQR信号十分微弱,湮没在噪声中,检测困难,这成为制约NQR技术发展的一项瓶颈. 为提升NQR信号信噪比,根据NQR信号的特点,提出了一种基于改进阈值函数小波变换的NQR信号去噪方法. 计算表明该方法可以有效消除外界噪声对信号的干扰,提高探测的准确性.      

Feedback optimization of pulse width in the SORC sequence.

A method for increasing the signal-to-noise ratio (SNR) of nuclear quadrupole resonance (NQR) measurements by automatically adjusting a pulse parameter in real-time is presented. This approach is useful in situations where the optimal pulse parameters cannot be chosen beforehand due to lack of knowledge regarding the system. For example, NQR provides a means for detecting explosives by revealing the presence of (14)N. In this particular application, the distance between the search coil and the explosive, as well as the temperature of the explosive, is unknown. As a result, a fixed set of pulse parameters will not yield the largest SNR for all possible search applications. This paper describes a feedback algorithm that uses measurements of the NQR signal to automatically adjust the pulse width in the strong off-resonant comb sequence to maximize the SNR of the NQR measurement. Experimental results obtained using a sample of sodium nitrite are presented.     

Long wavelength strain-engineered InAs multi-layer stacks quantum dots laser diode on GaAs substrate

The growth of GaAs based 1.5 ??m multi-layer stacked InAs quantum dots (QDs) has been investigated by solid-source molecular beam epitaxy (SSMBE), which was very important devices for transmission window. Owing to a strong electronic coupling between the QDs layers and the quantum wells (QWs), and antimony (Sb) introduced by for long-wavelength semiconductor lasers were obtained. The device structure for QDs laser diodes (LDs) with a cavity length of 1000 ??m and stripe width of 100 ??m as well as the device fabrication results will also be presented. The output performance was achieved with continuous wave (CW) operation, the measurement were from 20 to 60°C with a temperature step of 10°C. The threshold current density was 168 A/cm², and the CW operating up to 20 mW at room temperature (RT) was achieved.     

Detection of plastic explosives in luggage with14N nuclear quadrupole resonance spectroscopy

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%.     

Emission of nuclear quadrupole resonance from polycrystalline hexamethylenetetramine

The angular dependence of the nuclear quadrupole resonance (NQR) signal intensity emitted from polycrystalline hexamethylenetetramine has been analytically investigated for all directions for non-contact detection of chemicals by nuclear quadrupole resonance. The field pattern of the NQR signal from a column sample was measured. The emitted patterns were the same as that from a united single magnetic dipole, which fitted well to the estimation based on quadrupole principle axis system. This result is helpful to design an antenna for NQR remote detection.     

Noise-resilient multi-frequency surface sensor for nuclear quadrupole resonance

A planar nuclear quadrupole resonance (NQR) sensor has been developed. The sensor is resilient to environmental noise and is capable of simultaneous independent multi-frequency operation. The device was constructed as an open multimodal birdcage structure, in which the higher modes, generally not used in magnetic resonance, are utilized for NQR detection. These modes have smooth distributions of the amplitudes of the corresponding radiofrequency magnetic fields everywhere along the sensor’s surface. The phases of the fields, on the other hand, are cyclically shifted across the sensor’s surface. Noise signals coming from distant sources, therefore, induce equal-magnitude cyclically phase-shifted currents in different parts of the sensor. When such cyclically phase-shifted currents arrive at the mode connection point, they destructively interfere with each other and are cancelled out. NQR signals of polycrystalline or disordered substances, however, are efficiently detected by these modes because they are insensitive to the phases of the excitation/detection. No blind spots exist along the sensor’s surface. The sensor can be used for simultaneous detection of one or more substances in locations with environmental noise.     

New Methods for Detection of 14N NQR Frequencies

Nitrogen atoms are present in a number of solid explosives and illicit substances. The nuclear quadrupole resonance (NQR) spectra and spin?Clattice relaxation of the nitrogen atomic nucleus ¹⁴N can be used to characterize these compounds and to distinguish between possible crystal polymorphs. After the characteristic ¹⁴N NQR frequencies and spin?Clattice relaxation rates in a compound are determined, NQR can be used to detect this compounds and, in case of crystal polymorphs, also to determine the method of preparation. The ¹⁴N NQR frequencies and spin?Clattice relaxation rates are measured either by pulse NQR or by nuclear quadrupole double resonance (NQDR) based on magnetic field cycling. Here, we discuss several ¹H?C¹⁴N NQDR techniques which can be used to measure the ¹⁴N NQR frequencies and spin?Clattice relaxation rates under various experimental conditions. Some characteristic applications of these techniques are presented and discussed in details.     

NQR device for detecting plastic explosives,mines, and drugs

We describe a NQR device to detect plastic explosives, mines, and drugs and discuss design considerations.     

利用核四极矩共振技术探测炸药

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.     

基于核四极矩共振原理的炸药探测方法研究与实验

介绍了一种基于核四极矩共振（Nuclear Quadrupole Resonance, NQR）原理的炸药探测方法及其基本原理和其用于炸药探测的依据,提出了一种可行的基于核四极矩共振原理的炸药检测系统,描述了其结构组成、工作原理及实验方法,并给出了对黑索金（RDX）、梯恩梯（TNT）、奥克托今（HMX）、太恩（PETN）和特屈儿（TETRYL）炸药的测试实验结果. 实验表明该方法可行,能实现对以上炸药的探测.     

Modified steady-state free precession pulse sequences for the detection of pure nuclear quadrupole resonance

Modifications of the steady-state free precession multi-pulse technique for the effective detection of the nuclear quadrupole resonance (NQR) signals are proposed. These modifications are based on the use of composite pulses and enable the suppression of the coherent noise signals such as the magneto-acoustic and piezo-electric signals or the ringing signal from the NQR probe. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of C6H12N4 are also presented and convincingly demonstrate its effectiveness.     

A study of continuous-wave two-frequency NQR

A simple continuous-wave parallel to pulse version of a multifrequency nuclear quadrupole resonance (NQR) device was constructed and tested: two orthogonal radio-frequency (RF) fields were applied simultaneously at two suitable frequencies to a multilevel quadrupole probe (I⋝1). A modified superregenerative NQR oscillator-detector (SRO) was utilized. An additional coil and RF source were used to irradiate the sample at the second frequency. After tuning the SRO to a chosen NQR line, the signal proportional to the population difference of the corresponding pair of energy levels was monitored. When another suitable transition was saturated simultaneously, sharing one level with the monitored line, the corresponding population change was also reflected in the first signal intensity change. The phenomenon was examined for Sb nuclei in Sb₂S₃ powder at room temperature.     

Modified multipulse technique for the effective detection of pure nuclear quadrupole resonance

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.     

RF probe recovery time reduction with a novel active ringing suppression circuit

A simple Q-damper device for active probe recovery time reduction is introduced along with a straightforward technique for the circuit's component value optimization. The device is inductively coupled to a probe through a coupling transformer positioned away from the main coil, which makes the design independent of the coil type being used. The Q-damper is a tuned circuit, which is resonant at the same frequency as the probe and can be actively interrupted. When the circuit is interrupted, it is detuned and, thereby, is uncoupled from the probe, which operates normally. Turning the device on leads to re-coupling of the circuits and causes splitting of the probe's resonance line, which can be observed through its drive port. A resistance of an appropriate value is introduced into the Q-damper circuit, resulting in smoothing of the resonance splitting into one broad line, representing the coupled system's low-Q state, in which the energy stored in the main coil is efficiently dissipated. The circuit's component values are optimized by monitoring the shape of this low-Q state. Probe recovery time reduction by, approximately, an order of magnitude has been obtained with this device. Application of the device during an NQR experiment led to an increase in the signal-to-noise ratio by a factor of 4.9.     

一种改进的微弱NQR信号检测算法

核四极矩共振（NQR）是一种固态射频谱分析技术,可用于检测高危险爆炸物. 然而NQR信号本身非常弱,并且易受线圈的热噪声和外部射频干扰的影响,低信噪比限制了NQR的实际应用. 该文提出一种改进的微弱NQR信号检测算法. 首先利用Hankel矩阵方式下奇异值分解的方法,有效地抑制射频干扰和噪声,并将NQR信号分离出来. 然后提出了一种基于MUSIC谱估计的非线性最小二乘检测器,它既保证了高的频率分辨率,又大大降低了运算量. 仿真数据和实测数据结果表明该算法的有效性.     

Increasing 14N NQR signal by 1H-14N level crossing with small magnetic fields

NQR detection of materials, such as TNT, is hindered by the low signal-to-noise ratio at low NQR frequencies. Sweeping small (0-26 mT) magnetic fields to shift the (1)H NMR frequency relative to the (14)N NQR frequencies can provide a significant increase of the (14)N NQR signal-to-noise ratio. Three effects of (1)H-(14)N level crossing are demonstrated in diglycine hydrochloride and TNT. These effects are (1) transferring (1)H polarization to one or more of the (14)N transitions, including the use of an adiabatic flip of the (1)H polarization during the field sweep, (2) shortening the effective (14)N T(1) by the interaction of (1)H with the (14)N transitions, (3) "level transfer" effect where the third (14)N (spin 1) energy level or other (14)N sites with different NQR frequency are used as a reservoir of polarization which is transferred to the measured (14)N transition by the (1)H. The (14)N NQR signal-to-noise ratio can be increased by a factor of 2.5 for one (14)N site in diglycine hydrochloride (and 2.2 in TNT), even though the maximum (1)H frequency used in this work, 111 6 kHz, is only 30% larger than the measured (14)N frequencies (834 kHz for diglycine hydrochloride and 843 kHz for TNT).     

75As, 63Cu NMR and NQR characterization of selected arsenic minerals

The direct measurement and identification of solid state arsenic phases using ⁷⁵As NMR is made difficult by the simultaneous conditions of large quadrupole moment and low coordination symmetry in many compounds. However, specific arsenic minerals can efficiently be detected and discriminated via nuclear quadrupolar resonance (NQR). We report on the first NMR and NQR measurements in the natural minerals enargite (Cu₃AsS₄), niccolite (NiAs), arsenopyrite (FeAsS) and loellingite (FeAs₂). The NQR frequencies have been determined from both high-field NMR powder patterns and via zero-field frequency sweeps. Density functional theory (DFT) based ab initio calculations support the experimental results. The compounds studied here are common in terms of the known set of As-containing minerals. They are sometimes encountered in the context of base metal or gold mining. The study represents a significant addition to the list of arsenic minerals that can now be detected with NQR techniques.     

爆炸物检测中NQR信号的处理及判识

介绍了基于核四极矩技术的爆炸物检测原理及信号处理方法.系统分析了NQR信号检测中主要误差来源,提出多种方法消除NQR信号处理中检测误差,主要包括相关累加消除随机噪声;单通道自适应消除振铃影响;相关性检测抑制同频干扰.实验表明相关检测可有效提高NQR信号信噪比,提高微弱NQR信号检测的准确性.