共查询到20条相似文献,搜索用时 31 毫秒
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《Physics letters. A》2006,358(4):322-326
Modification of the steady-state free precession (SSFP) multi-pulse technique for the effective detection of the NQR signals in the presence of a strong coherent noise is proposed. This modification based on the use of additional blocks of the pulses and phase cycling technique enables the suppression of the coherent noise signals such as the magneto-acoustic and piezoelectric signals or the ringing signals from the NQR probe. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of RDX (C3H6N6O6) are presented and convincingly demonstrate its effectiveness. 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
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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. 相似文献
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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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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
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The nuclear quadrupole resonance (NQR) method has been applied to Heroin Base (HB) to find an optimised multi-pulse technique for effective detection of HB. Experimental results of applying the proposed spin-locking multi-pulse (SLMP) technique to nitrogen-14 NQR in this sample are presented and convincingly demonstrate as a path towards efficient detection. A detection using a sequence of this character could be achieved over real-world scan volumes for screening of goods. All experiments were carried out at room temperature. 相似文献
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氮-14远程核四极共振谱仪 总被引:1,自引:1,他引:0
为了满足检测与探头有一定距离的含氮化合物的核四极共振信号,本文研制了一台结构简单,造价低廉的核四极共振操测仪.它利用了脉冲付里叶变换技术,可将获得的核自由感应衰减信号或者回波信号进行相干累加.整个系统分硬件和软件两大部分.前者由射频脉冲放大器(约500W脉冲输出功率),探头,接收机,MCS-96型单片机和PC机构成.后者由单片机上的脉冲序列程序与PC机上的数值信号处理程序组成.利用这台谱仪,可以在几十秒时间内得到距离探头线圈10cm内的典型14 N样品的核四极共振谱. 相似文献
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T. N. Rudakov 《Applied magnetic resonance》2012,43(4):557-566
The nuclear quadrupole resonance (NQR) method has been applied to ammonium nitrate (AN)-based explosives, ANFO and REOGEL+, to find an optimized multi-pulse technique for effective detection. The relaxation parameters and signal intensities for nitrogen-14 lines of these substances were measured. The experimental results of applying the proposed multi-pulse technique in these samples are presented and convincingly demonstrate a path toward efficient detection. A detection using sequences of this character could be achieved over real-world scan volumes for screening of goods. It was proven that the cross-polarization technique can significantly enhance the NQR signal for AN-based explosives. 相似文献
11.
G. B. Soifer 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(5):765-769
The activation energy of thermoactivated molecular motions in solids is determined by examining the influence of these motions
on the temperature dependence of the nuclear quadrupole spin-lattice relaxation rate and quadrupole resonance (NQR) signal
intensity for chlorine-35. In the latter case, the heating of the crystals is accompanied by the fading of resonance signals,
which is analyzed using a linear correlation between the activation energy of this motion and the fade-out temperature. The
correlation parameters are demonstrated to be dependant on the type of molecular motion. The relaxation method is shown to
be more effective in studying molecular motion and evaluating its activation energy as compared to the NQR signal fading technique. 相似文献
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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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Application of the Wavelet Transform for Detecting Signals of Nuclear Quadrupole Resonance 总被引:1,自引:0,他引:1
In the present study, the wavelet transform is used to increase the signal-to-noise ratio of nuclear quadrupole resonance (NQR) signals in the direct pulse method. The efficiency of the wavelet and Fourier transforms used for detecting the NQR signal component is compared. The signal consists of noise, magnetoacoustic and piezoelectric signals, noise from external sources, and NQR signal. Signals from 14
N nuclei in hexahydro-1,3,5-trinitro-s-triazine C3H6N6O6 (RDX) are investigated at a temperature of 298 K.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 47–50, January, 2005. 相似文献
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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. 相似文献
18.
Peshkovsky AS Cattena CJ Cerioni LM Osán TM Forguez JG Peresson WJ Pusiol DJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,194(2):222-229
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. 相似文献
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The non-cyclic geometric phase of 14N and 35Cl NQR signals induced by the character of trajectory of nuclear magnetization motion upon pulse r.f. excitation of powdered samples is studied. Analytical expressions for the geometric phases of NQR signals of the nuclei of spins I=1 and 3/2 upon nuclear magnetization rotation induced by means of r.f. pulses with frequency detuned from the resonance and for any impulse duration for a separate crystallite are obtained. It is shown that the geometric phase recorded for the signal from a powdered sample at Δω=0 can be different from zero and can oscillate upon changes in duration of the r.f. excitation pulse. An alternative variant of the nutation experiment aimed at obtaining the asymmetry parameter η from locations of frequency singularities in the nutation phase spectrum for nuclei of spin I=3/2 in powder substances is proposed. 相似文献
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Various methods for measuring multivariate nutation NQR spectra under off-resonance conditions are considered. A method is proposed which is based on optimum filtration. An experimental Cl-35 3D nutation NQR spectrum of chloral hydrate is reported for the first time. 相似文献