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Highlights • This paper introduces a two-channel echo-train (TE) data acquisition system used in NQR signal detection and discovers/proves the beamforming characteristics of the TE system. • A novel beamforming approach based on this TE system is proposed which can nicely cancel interference within NQR resonance spectrum. • The proposed algorithm has excellent performance on detecting NQR signal polluted by interference and is superior to previously proposed algorithms, including the classical beamforming algorithms/detectors constructed on the TE system. Abstract Interference can be a huge challenge for Nuclear Quadrupole Resonance (NQR) signal detection in real life settings. The problem is particularly challenging when interference is strong around the resonant frequency band of the targeted NQR signal (to which we refer as the NQR band). This paper first proves the beamforming characteristics of a designed two-channel echo-train (TE) data acquisition system, and then presents a novel beamforming approach which is based on the TE system and is able to cancel interference effectively within the NQR band. After interference cancellation, NQR signal detection can be done successfully by applying an "echo train" approximate maximum likelihood (ETAML) algorithm to the residual data. The proposed algorithm is shown to be superior to previously proposed algorithms, including the classical beamforming algorithms/detectors constructed on the TE system, for detecting NQR signal polluted by interference. [ABSTRACT FROM AUTHOR]

Nuclear quadrupole resonance (NQR) spectroscopy is proven to be a very sensitive technique for measuring distribution of electric charge around quadrupolar nuclei. Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. The electronic structure of magnesium alanate, Mg(AlH4)2, as promising hydrogen storage materials for hydrogen fuel cell-powered automobile applications, has been studied in detail by ab initio calculated NQR parameters. Furthermore, using calculated nuclear quadrupole coupling constants (NQCCs) of hydrogen atoms (²H-NQCC), the electronic structure of α-Mg(AlH4)2 with its high-pressure forms, β- and γ- Mg(AlH4)², was compared. The electric field gradient (EFG) at the site of 2H atoms was calculated to obtain NQCC parameters. The results show that in the γ-Mg(AlH4)2, 2H-NQCCs are smaller than that of other considered phases. In other words, Al-H bonds in γ-Mg(AlH4)2 nanocrystal is weaker than others and the charge transfer from Al to hydrogen atom is less than the others and therefore these hydrogens have weaker bonds with Al and easier condition for dehydrogenation is expected in γ-Mg(AlH4)². Comparison of calculated dehydrogenation enthalpies of various Mg(AlH4)2 phases verifies this prediction. All calculations performed using Gaussian 03 at the HF/3-21G level of theory. The selected level and basis set give the rather acceptable qualitative NQCCs of hydrogen atoms. [ABSTRACT FROM AUTHOR]

Nuclear quadrupole resonance spectroscopy is an analytical method which allows to characterize materials which contain quadrupolar nuclei, i.e. nuclei with spin ⩾1. The measurement technology is similar to that of NMR except that no static magnetic field is necessary. In contrast to NMR, however, it is frequently necessary to scan spectra with a very large bandwidth with a span of several tens of % of the central frequency so as to localize unknown peaks. Standard NMR probeheads which are typically constructed as resonators must be tuned and matched to comparatively narrow bands and must thus be re-tuned and re-matched very frequently when scanning over a whole NQR spectrum. At low frequencies up to few MHz dedicated circuits without the need for tuning and matching have been developed, but many quadrupole nuclei have transitions in the VHF range between several tens of MHz up to several hundreds of MHz. Currently available commercial NQR probeheads employ stepper motors for setting mechanically tuneable capacitors in standard NMR resonators. These yield high quality factors (Q) and thus high SNR but are relatively large and clumsy and do not allow for fast frequency sweeps. This article presents a new concept for a NQR probehead which combines a previously published no-tune no-match wideband concept for the transmit (TX) pulse with an electronically tuneable receive (RX) part employing varactor diodes. The prototype coil provides a TX frequency range of 57 MHz with a center frequency of 97.5 MHz with a return loss of ⩽−15 dB. During RX the resonator is tuned and matched automatically to the right frequency via control voltages which are read out from a previously generated lookup table, thus providing high SNR. The control voltages which bias the varactors settle very fast and allow for hopping to the next frequency point in the spectrum within less than 100 μs. Experiments with a test sample of ZnBr 2 proved the feasibility of the method. [ABSTRACT FROM AUTHOR]

Nuclear quadrupole resonant spectroscopy is method similar to nuclear magnetic resonant spectroscopy also called zero field NMR [1, 2]. The response signal magnitude is very low and it is immersed in to the noise. There can be used some methods to harvest signal from noise it can be matched receiver [3] or averaging. This authors describe detector for Nuclear quadrupole resonant spectroscopy based on statistic methods and probability of distribution, that allow to measure repetitive signals below noise level. The paper presents the mathematical model and practical solution of the detector, and problems such as the dynamic range and signal distortion based on the signal-to-noise ratio are also analyzed in the given context. If the time of signal occurrence is known, the repetitive signal below the noise level can be harvested out of noise by averaging because of the wanted signal is correlated therefor highlighted by averaging contrast to the noise which is not correlated so it is supressed by averaging. The same principle we can use in domain of digital signal. So the input signal can be converted to the digital representation. There is an comparator with a triggering level immersed in the noise so the comparator is flipping continuously and the probability of output values is affected by input signal. The output digital signal can be processed by FPGA. [ABSTRACT FROM AUTHOR]

Abstract: Unlimited solid solution Fe1−x Co x Ga3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T 1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N 2(E F ). [Copyright &y& Elsevier]

Abstract: The experiment with phase inversion and phase-inverted echo-amplitude detected nutation (PEANUT) was introduced in the nuclear quadrupole resonance (NQR). Formulas were obtained describing the NQR (I=3/2) experiment. Exemplary experiments are provided confirming the predicted particularities of the PEANUT spectra in NQR Cl-35. It is proposed to apply the method for the purpose of determination the asymmetry parameter of the electric field gradient (EFG) tensor in powders with the help of the analysis of PEANUT interferograms. Application of two-dimensional PEANUT experiments, in which the nutation frequencies correlate with the resonance NQR frequencies, can substantially simplify the interpretation of complex spectra. [Copyright &y& Elsevier]

Abstract: While the synthetic utility and reactivity of the so-called “GaI” species is reasonably well established, its exact composition remains unknown. Using primarily multinuclear magnetic resonance techniques (and supported with powder X-ray diffraction measurements), we offer some new insights into the composition of “GaI”. Using 127I nuclear quadrupole resonance (NQR) experiments, it is clearly demonstrated that gallium diiodide (GaI2) is a significant component of this material, while GaI3 is not. This finding is in contrast with a prior literature account, which noted that Ga2I3 (i.e., one equivalent of GaI3 per equivalent of Ga metal) was present in significant amounts. Additional solid-state nuclear magnetic resonance (SSNMR) experiments using the 69/71Ga probe nuclei in multiple magnetic fields clearly establish, via its diagnostic Knight-shifted resonance, the presence of Ga0 metal, which is in agreement with prior literature. Taken together, a composition may be tentatively offered: that “GaI” is, to a large extent, two equivalents of Ga0 metal with two equivalents of GaI2, where the latter is composed of Ga+ and ions. This composition may be represented as [Ga0]2[Ga]+[GaI4]−. [Copyright &y& Elsevier]

Abstract: The acquisition of nuclear quadrupole resonance (NQR) spectra with wideband uniform rate and smooth truncation (WURST) pulses is investigated. 75As and 35Cl NQR spectra acquired with the WURST echo sequence are compared to those acquired with standard Hahn-echo sequences and echo sequences which employ composite refocusing pulses. The utility of WURST pulses for locating NQR resonances of unknown frequency is investigated by monitoring the integrated intensity and signal to noise of 35Cl and 75As NQR spectra acquired with transmitter offsets of several hundreds kilohertz from the resonance frequencies. The WURST echo sequence is demonstrated to possess superior excitation bandwidths in comparison to the pulse sequences which employ conventional monochromatic rectangular pulses. The superior excitation bandwidths of the WURST pulses allows for differences in the characteristic impedance of the receiving and excitation circuits of the spectrometer to be detected. Impedance mismatches have previously been reported by Marion and Desvaux [D.J.Y. Marion, H. Desvaux, J. Magn. Reson. (2008) 193(1) 153–157] and Muller et al. [M. Nausner, J. Schlagnitweit, V. Smrecki, X. Yang, A. Jerschow, N. Muller, J. Magn. Reson. (2009) 198(1) 73–79]. In this regard, WURST pulse sequences may afford an efficient new method for experimentally detecting impedance mismatches between receiving and excitation circuits, allowing for the optimization of solids and solution NMR and NQR spectrometer systems. The use of the Carr–Purcell Meiboom–Gill (CPMG) pulse sequence for signal enhancement of NQR spectra acquired with WURST pulses and conventional pulses is also investigated. Finally, the utility of WURST pulses for the acquisition of wideline NQR spectra is demonstrated by acquiring part of the 63/65Cu NQR spectrum of CuCN. [ABSTRACT FROM AUTHOR]

Abstract: In spite of a renewed interest in Nuclear Quadrupole Resonance (NQR), especially of nitrogen-14 (for instance, for the detection and characterization of explosives), a full NQR instrument, ready to use in the laboratory, is not commercially available. We describe here an entirely homemade spectrometer, reasonably transportable, including the transmit-receive system, frequency generation, data acquisition, probes and a specialized software for driving the instrument and for data processing. [Copyright &y& Elsevier]

Nuclear quadrupole resonance (NQR) offers an unequivocal method of detecting hidden narcotics and explosives. Unfortunately, the practical use of NQR is restricted by the low signal-to-noise ratio (SNR) and means to improve the SNR are vital to enable a rapid, reliable and convenient system. In this correspondence, we develop two multichannel detectors to counter the typically present radio frequency interference. Numerical simulations indicate that the proposed methods offers a significantly improved robustness to uncertainties in the parameters detailing the examined sample. [ABSTRACT FROM AUTHOR]

Nuclear Quadrupole Resonance (NQR) spectroscopy has been known for 70 years. It is suitable for the study of measured (poly)crystalline chemical compounds containing quadrupole nuclei (nuclei with spin I ≥ 1) where the characteristic NQR frequencies represent the fingerprints of these compounds. In several cases, 14N NQR can distinguish between the polymorphic crystalline phases of active pharmaceutical ingredients (APIs). In order to further stimulate 14N NQR studies, we review here several results of API polymorphism studies obtained in Ljubljana laboratories: (a) In sulfanilamide, a clear distinction between three known polymorphs (α, β, γ) was demonstrated. (b) In famotidine, the full spectra of all seven different nitrogen positions were measured; two polymorphs were distinguished. (c) In piroxicam, the 14N NQR data helped in confirming the new polymorphic form V. (d) The compaction pressure in the tablet production of paracetamol, which is connected with linewidth change, can be used to distinguish between producers of paracetamol. We established that paracetamol in the tablets of six different manufacturers can be identified by 14N NQR linewidth. (e) Finally, in order to get an extremely sensitive 14N NQR spectrometer, the optical detection of the 14N NQR signal is mentioned. [ABSTRACT FROM AUTHOR]

The effect of uniaxial tensile strain on spin coherence in n-type GaAs epilayers is probed using time-resolved Kerr rotation, photoluminescence, and optically detected nuclear magnetic resonance spectroscopies. The band gap, electron spin lifetime, electron g factor, and nuclear quadrupole splitting are simultaneously imaged over millimeter scale areas of the epilayers for continuously varying values of strain. All-optical nuclear magnetic resonance techniques allow access to the strain-induced nuclear quadrupolar resonance splitting in field regimes not easily addressable using conventional optically detected nuclear magnetic resonance. [ABSTRACT FROM AUTHOR]

Based on the previous identification of metastable polymorphs in crystalline triphenylbismuth by nuclear quadrupole resonance spectroscopy (NQRS), the potential formation of similar phases was studied in Tris(2-Methoxyphenyl)Bismuthine. To this end, commercial samples with known NQRS properties were molten and re-crystallized at different speeds (shock freezing in different coolants versus slow cooling inside of a heater). In all recrystallization products we have identified a new crystal phase which has not been observed after synthesis from a solution. The new crystallographic structure has been confirmed by X-ray diffraction (XRD). The newly isolated polymorph crystallizes in the monoclinic space group P2(1)/c with only one molecule in the asymmetric unit and consequently only one 5/2-7/2 transition is observed at 88.75 MHz at 310 K. In contrast, the two transitions at 89.38 and 89.29 MHz for the well-known trigonal polymorph originate from two crystallographically distinct molecules of Tris(2-methoxy-Phenyl)Bismuthine in the asymmetric unit. Additional relaxometric NQRS shows distinctly different T2 relaxation times for the new polymorph when compared to the original samples. Additional phase transitions could not be observed during temperature sweeps between 153 K and 323 K. [ABSTRACT FROM AUTHOR]