Topic
Nuclear quadrupole resonance
About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.
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TL;DR: A novel NQR data model of the full echo train and detail why and how these echo trains are produced is proposed and two recently proposed approximative maximum-likelihood detectors are refined that enable the algorithms to optimally exploit the proposed echo train model.
Abstract: Nuclear quadrupole resonance (NQR) is a radio-frequency technique that can be used to detect the presence of quadrupolar nuclei, such as the 14N nucleus prevalent in many explosives and narcotics. In a typical application, one observes trains of decaying NQR echoes, in which the decay is governed by the spin echo decay time(s) of the resonant line(s). In most detection algorithms, these echoes are simply summed to produce a single echo with a higher signal-to-noise ratio, ignoring the decaying echo structure of the signal. In this paper, after reviewing current NQR signal models, we propose a novel NQR data model of the full echo train and detail why and how these echo trains are produced. Furthermore, we refine two recently proposed approximative maximum-likelihood detectors that enable the algorithms to optimally exploit the proposed echo train model. Extensive numerical evaluations based on both simulated and measured NQR data indicate that the proposed detectors offer a significant improvement as compared to current state-of-the-art detectors
59 citations
TL;DR: Anisotropic displacement parameters for H atoms in molecular crystals are calculated with a simplified model that uses approximate vibrational modes, neglecting correlations between internal and external contributions to the mean square motions as mentioned in this paper.
59 citations
TL;DR: In this article, the possibilities of detecting nuclear quadrupole resonance (NQR) signals in explosives and drugs are considered. Direct and indirect NQR techniques for searching substances are described and the potentialities of various experimental methods are compared.
Abstract: Possibilities of detecting nuclear quadrupole resonance (NQR) signals in explosives and drugs are considered. Direct and indirect NQR techniques for searching substances are described and the potentialities of various experimental methods are compared.
59 citations
TL;DR: In this article, the spin-lattice relaxation times (T/sub 1/) were either shorter than 0.3 ms or longer than 60 ms, and the short relaxation times were interpreted as arising from the interaction with conduction electrons, which could be used to distinguish between metallic and nonconducting substructures.
Abstract: /sup 63/Cu and /sup 65/Cu nuclear quadrupole resonance (NQR) results of eleven YBa/sub 2/Cu/sub 3/O/sub x/ samples with x ranging from 7.00 to 6.00 are reported. All measurements were done at room temperature. An attempt was made to quantify integrated signal intensities. The spin-lattice relaxation times (T/sub 1/) were either shorter than 0.3 ms or longer than 60 ms. Because the short relaxation times are interpreted as arising from the interaction with conduction electrons, the T/sub 1/'s could be used to distinguish between metallic and nonconducting substructures. In the 7.0
58 citations
TL;DR: In this article, the magnetic and superconducting properties of (La 1- x Ba x ) 2 CuO 4 systems have been investigated in terms of 139 La nuclear quadrupole resonance (NQR).
Abstract: Both the magnetic and superconducting properties of (La 1- x Ba x ) 2 CuO 4 systems have been investigated in terms of 139 La nuclear quadrupole resonance (NQR). For La 2 CuO 4 , it has clearly been demonstrated that the internal field H n is applied on the La site by magnetic ordering below ∼240 K. The observed H n is not consistently explained by the spin structure proposed in the neutron diffraction study. For the doped compound with x =0.01, the internal field at 1.3 K was almost the same as that for La 2 CuO 4 , while for x =0.025, it decreased and was significantly distributed. Furthermore, the superconductivity was found to set in around 2 K. From a microscopic point of view, it is concluded that the magnetic ordering and superconductivity compete around x =0.025.
58 citations