Showing papers on "Nuclear quadrupole resonance published in 2018"

209Bi quadrupole relaxation enhancement in solids as a step towards new contrast mechanisms in magnetic resonance imaging.

Abstract: Motivated by the possibility of exploiting species containing high spin quantum number nuclei (referred to as quadrupole nuclei) as novel contrast agents for Magnetic Resonance Imaging, based on Quadrupole Relaxation Enhancement (QRE) effects, 1H spin-lattice relaxation has been investigated for tris(2-methoxyphenyl)bismuthane and tris(2,6-dimethoxyphenyl)bismuthane in powder. The relaxation experiment has been performed in the magnetic field range of 0.5 T to 3 T (the upper limit corresponds to the field used in many medical scanners). A very rich QRE pattern (several frequency specific 1H spin-lattice relaxation rate maxima) has been observed for both compounds. Complementary Nuclear Quadrupole Resonance experiments have been performed in order to determine the quadrupole parameters (quadrupole coupling constant and asymmetry parameters) for 209Bi. Knowing the parameters, the QRE pattern has been explained on the basis of a quantum-mechanical picture of the system including single and double-quantum coherences for the participating nuclei (1H and 209Bi). In this way the quantum-mechanical origin of the spin transitions leading to the QRE effects has been explained.

79/81Br nuclear quadrupole resonance spectroscopic characterization of halogen bonds in supramolecular assemblies.

Abstract: Despite the applicability of solid-state NMR to study the halogen bond, the direct NMR detection of 79/81Br covalently bonded to carbon remains impractical due to extremely large spectral widths, even at ultra-high magnetic fields. In contrast, nuclear quadrupole resonance (NQR) offers comparatively sharp resonances. Here, we demonstrate the abilities of 79/81Br NQR to characterize the electronic changes in the C–Br⋯N halogen bonding motifs found in supramolecular assemblies constructed from 1,4-dibromotetrafluorobenzene and nitrogen-containing heterocycles. An increase in the bromine quadrupolar coupling constant is observed, which correlates linearly with the halogen bond distance (dBr⋯N). Notably, 79/81Br NQR is able to distinguish between two symmetry-independent halogen bonds in the same crystal structure. This approach offers a rapid and reliable indication for the occurrence of a halogen bond, with experimental times limited only by the observation of 79/81Br NQR resonances.

Signal Processing and Analysis Methods in Nuclear Quadrupole Resonance Spectroscopy

Abstract: The purpose of this paper is to review the signal processing and analysis methods applied in nuclear quadrupole resonance (NQR) spectroscopy. NQR is a radio frequency spectroscopic technique used for detecting solid state compounds containing quadrupolar nuclei, in applications ranging from chemical analysis to explosive and drugs detection. This paper presents the principle of NQR, its applications, the detection methods and an overview of the research done in the field of signal processing and analysis using this technique. Different solutions are described, starting from the techniques developed initially up to state-of-the-art detection algorithms. These are presented in chronological order, also discussing their principles, advantages and disadvantages. This paper proposes several directions for future research and suggests machine learning as a next step in NQR signal analysis.

Tuning Nuclear Quadrupole Resonance: A Novel Approach for the Design of Frequency-Selective MRI Contrast Agents

Abstract: The interaction between water protons and suitable quadrupolar nuclei (QN) can lead to quadrupole relaxation enhancement (QRE) of proton spins, provided the resonance condition between both spin tr ...

Structural phase transition, antiferromagnetism and two superconducting domes in LaFeAsO 1-x F x (0 < x ≤ 0.75)

Abstract: We report 75As nuclear magnetic resonance (NMR)/nuclear quadrupole resonance (NQR) and transmission electron microscopy (TEM) studies on LaFeAsO1−xFx. There are two superconducting domes in this material. The first one appears at 0.03 ≤ x ≤ 0.2 with T c max = 27 K, and the second one at 0.25 ≤ x ≤ 0.75 with T c max = 30 K. By NMR and TEM, we demonstrate that a C4-to-C2 structural phase transition (SPT) takes place above both domes, with the transition temperature Ts varying strongly with x. In the first dome, the SPT is followed by an antiferromagnetic (AF) transition, but neither AF order nor low-energy spin fluctuations are found in the second dome. By 75As nuclear spin-lattice relaxation rate (1/T1) measurements, we find that AF order and superconductivity coexist microscopically in LaFeAsO0.97F0.03. In the coexisting region, 1/T1 decreases at Tc but becomes proportional to T below 0.6Tc, indicating gapless excitations. Therefore, in contrast to the early reports, the obtained phase diagram for x ≤ 0.2 is quite similar to the doped BaFe2As2 system. The electrical resistivity ρ in the second dome can be fitted by ρ = ρ0 + ATn with n = 1 and a maximal coefficient A at around xopt = 0.5-0.55 at which Ts extrapolates to zero and Tc is the maximal, which suggests the importance of quantum critical fluctuations associated with the SPT. We have constructed a complete phase diagram of LaFeAsO1−xFx, which provides insight into the relationship between SPT, antiferromagnetism and superconductivity.

An automated instrument for polarization-enhanced broadband nuclear quadrupole resonance (NQR) spectroscopy.

Abstract: An automated instrument for improving the sensitivity of nuclear quadrupole resonance (NQR) spectroscopy is presented. The device is capable of pre-polarizing samples within a custom Halbach-type permanent magnet and then moving them into an external probe for zero-field NQR detection. Polarization transfer between protons and nitrogen (14N) nuclei in the sample occurs during demagnetization, thus increasing the amplitude of the detected NQR signals. The sample motion profile is completely programmable, thus providing a high level of control over the sample position and velocity for optimizing the polarization transfer process for various samples. Moreover, the magnet and motion controller are combined with a shielded sample probe and ultra-broadband front-end electronics (both designed in-house) to realize a complete scientific instrument for 14N NQR experiments. Compared with previous work in the field, the system is designed to be programmable, robust, and easy to use. Experimental results from several samples are also presented.

Authentication of dietary supplements through Nuclear Quadrupole Resonance (NQR) spectroscopy

Abstract: As the industry grows, adulteration of many products by mislabelling, re-branding and false advertising is becoming prevalent practice. Existing solutions for analysis often require extensive sample preparation or are limited in terms of detecting different types of integrity issues. We describe a novel authentication method based on Nuclear Quadrupole Resonance (NQR) spectroscopy which is quantitative, non-invasive and non-destructive. It is sensitive to small deviation in the solid-state chemical structure of a product, which changes the NQR signal properties. These characteristics are unique for different manufacturers, resulting in manufacturer-specific watermarks. We show that nominally identical dietary supplements from different manufacturers can be accurately classified based on features from NQR spectra. Specifically, we use a machine learning-based classification called support vector machines (SVMs) to verify the authenticity of products under test. This approach has been evaluated on three products using semi-custom hardware and shows promising results, with typical classification accuracy of over 95%.

Antiferromagnetic ground state in the MnGa$_4$ intermetallic compound

Abstract: Magnetism of the binary intermetallic compound MnGa$_4$ is re-investigated. Band-structure calculations predict antiferromagnetic behavior in contrast to Pauli paramagnetism reported previously. Magnetic susceptibility measurements on single crystals indeed reveal an antiferromagnetic transition at $T_N=393$ K. Neutron powder diffraction and $^{69,71}$Ga nuclear quadrupole resonance spectroscopy show collinear antiferromagnetic order with magnetic moments alligned along the [111] direction of the cubic unit cell. The magnetic moment of 0.80(3)$\mu_B$ at 1.5 K extracted from the neutron data is in good agreement with the band-structure results.

Model – free approach to quadrupole spin relaxation in solid 209Bi-aryl compounds

Abstract: Nuclear Quadrupole Resonance (NQR) experiments were performed for deuterated and non-deuterated triphenylbismuth (BiPh3) to inquire into 209Bi relaxation mechanisms. The studies are motivated by the idea of exploiting Quadrupole Relaxation Enhancement (QRE) as a novel contrast mechanism for Magnetic Resonance Imaging. From this perspective relaxation features of nuclei possessing quadrupole moment (quadrupole nuclei) are of primary importance for the contrast effect. Spin–spin relaxation rates associated with the NQR lines were described in terms of the Redfield relaxation theory assuming that the relaxation is caused by fluctuations of the electric field gradient tensor at the position of the quadrupole nucleus that are described by an exponential correlation function. The description referred to as a model-free approach is an analogy of the description used for paramagnetic contrast agents. It was demonstrated that for the deuterated compound this approach captures the essential features of 209Bi relaxation, but it should not be applied for non-deuterated compounds as dipolar interactions between neighbouring protons and the quadrupole nucleus considerably contribute to the relaxation of the last one. Thus, the relaxation scenario for species containing quadrupole nuclei is fundamentally different than for paramagnetic contrast agents and this fact has to be taken into account when predicting contrast effects based on QRE.

Spin coherent states phenomena probed by quantum state tomography in Zeeman perturbed nuclear quadrupole resonance

Abstract: Recently, we reported an experimental implementation of quantum information processing (QIP) by nuclear quadrupole resonance (NQR). In this work, we present the first quantum state tomography (QST) experimental implementation in the NQR QIP context. Two approaches are proposed, employing coherence selection by temporal and spatial averaging. Conditions for reduction in the number of cycling steps are analyzed, which can be helpful for larger spin systems. The QST method was applied to the study of spin coherent states, where the alignment-to-orientation phenomenon and the evolution of squeezed spin states show the effect of the nonlinear quadrupole interaction intrinsic to the NQR system. The quantum operations were implemented using a single-crystal sample of KClO $$_{3}$$ and observing $$^{35}$$ Cl nuclei, which posses spin 3/2.

Single ferromagnetic fluctuations in UCoGe revealed by 73 Ge- and 59 Co-NMR studies

Abstract: $^{73}$Ge and $^{59}$Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed on a $^{73}$Ge-enriched single-crystalline sample of the ferromagnetic superconductor UCoGe in the paramagnetic state. The $^{73}$Ge NQR parameters deduced from NQR and NMR are close to those of another isostructural ferromagnetic superconductor URhGe. The Knight shifts of the Ge and Co sites are well scaled to each other when the magnetic field is parallel to the $b$ or $c$ axis. The hyperfine coupling constants of Ge are estimated to be close to those of Co. The large difference of spin susceptibilities between the $a$ and $b$ axes could lead to the different response of the superconductivity and ferromagnetism with the field parallel to these directions. The temperature dependence of the nuclear spin-lattice relaxation rates $1/T_1$ at the two sites is similar to each other above 5 K. These results indicate that the itinerant U-$5f$ electrons are responsible for the ferromagnetism in this compound, consistent with previous studies. The similarities and differences in the three ferromagnetic superconductors are discussed.

Fabrication of low cost and versatile internal field pulsed nuclear magnetic resonance spectrometer to study the magnetic materials

Abstract: We have built a low cost and versatile pulsed internal field nuclear magnetic resonance (IFNMR) spectrometer and used it to study ferromagnetic materials. Initially optimization of the instrument has been tested with nuclear quadrupole resonance (NQR) active nuclei. Ferromagnetic materials like bulk iron, bulk cobalt and carbon coated cobalt nanopowder have been used as the testing materials for our spectrometer. Preliminary results obtained from the present spectrometer have been compared with the earlier reports and are in good agreement. The specifications and performance standard of the instrument match quite well with standard instruments elsewhere in the world which is testified with the observation of NMR echo signals in the above mentioned materials confirming the quality of the spectrometer. Additionally NMR signals from the grain boundaries are observed in Co@C nanomaterials which prove the sensitivity of the spectrometer.

Detection of NQR signals using wavelet transform and adaptive filters

Abstract: NQR signal processing method based on two adaptive filters techniques namely adaptive noise cancellation (ANC), adaptive line enhancement (ALE) and wavelet transform are studied and it is shown that ALE is faster detection method with improved signal to noise ratio. Based on the 14N NQR signal observed from NaNO2, ALE seems to be easier and more reliable technique for NQR spectroscopy.

Superlattice formation lifting degeneracy protected by non-symmorphic symmetry through a metal-insulator transition in RuAs

Abstract: The single crystal of RuAs obtained by Bi-flux method shows obvious successive metal-insulator transitions at T_MI1~255 K and T_MI2~195$ K. The X-ray diffraction measurement reveals a formation of superlattice of 3x3x3 of the original unit cell below T_MI2, accompanied by a change of the crystal system from the orthorhombic structure to the monoclinic one. Simple dimerization of the Ru ions is nor seen in the ground state. The multiple As sites observed in nuclear quadrupole resonance (NQR) spectrum also demonstrate the formation of the superlattice in the ground state, which is clarified to be nonmagnetic. The divergence in 1/T_1 at T_MI1 shows that a symmetry lowering by the metal-insulator transition is accompanied by strong critical fluctuations of some degrees of freedom. Using the structural parameters in the insulating state, the first principle calculation reproduces successfully the reasonable size of nuclear quadrupole frequencies for the multiple As sites, ensuring the high validity of the structural parameters. The calculation also gives a remarkable suppression in the density of states (DOS) near the Fermi level, although the gap opening is insufficient. A coupled modulation of the calculated Ru d electron numbers and the crystal structure proposes a formation of charge density wave (CDW) in RuAs. Some lacking factors remain, but it shows that a lifting of degeneracy protected by the non-symmorphic symmetry through the superlattice formation is a key ingredient for the metal-insulator transition in RuAs.

Magnetic inhomogeneity in the copper pseudochalcogenide CuNCN

Abstract: Copper carbodiimide, CuNCN, is a geometrically frustrated nitrogen-based analogue of cupric oxide, whose magnetism remains ambiguous. Here, we employ a combination of local-probe techniques, including $^{63,\, 65}$Cu nuclear quadrupole resonance, $^{13}$C nuclear magnetic resonance and muon spin rotation to show that the magnetic ground state of the Cu$^{2+}$ ($S=1/2$) spins is frozen and disordered. Moreover, these complementary experiments unequivocally establish an onset of intrinsically inhomogeneous magnetic state at $T_h=80$ K. Below $T_h$, the low-temperature frozen component coexist with the remnant high-temperature dynamical component down to $T_l = 20$ K, where the latter finally ceases to exist. Based on a scaling of internal magnetic fields of both components we conclude that the two components coexist on a microscopic level.

Study of Dehydrogenation of Pressure-induced NaBH4 Structures Using Calculated NQCC Parameters

Abstract: Nuclear quadrupole resonance (NQR) spectroscopy is an accurate method for determination of electric charge distribution around quadrupolar nuclei. Using ab initio computational methods, it is possible to calculate the Nuclear Quadrupole Coupling Constants (NQCCs) with high accuracy and obtain the useful structural information by using these parameters. Sodium Borohydride, NaBH4, is a metal hydride complex which is a good candidate for being applied in fuel cells as hydrogen storage material with high capacity of 10.6 wt %. Despite the high capacity of hydrogen storage, hydrogen desorption occurs at high temperatures due to high stability and strong bonds of this compound. This problem limits the practical usage of NaBH4 in fuel cells. One way to overcome this problem is applying the high-pressure techniques and using the pressure-induced NaBH4 structures. Under ambient conditions, NaBH4 has a cubic structure (α-NaBH4) that can be converted to β- and γ-NaBH4 by increasing the pressure. In the present research, charge distribution of α-NaBH4 nanocrystal has been compared to that of high-pressure structures using calculated NQCCs, to study the effect of pressure on different NaBH4 structures and hydrogen desorption ability of them. Our results show the smaller value of 2H–NQCCs and higher value of 11B-NQCCs for β-NaBH4 respect to other structures. In other words, the B-H bond is weaker in β-NaBH4 and it is expected that dehydrogenation occur more feasible and at lower temperature in β-phase compared to other phases. NBO results are in agreement with Calculated NQCCs. Calculations performed using Gaussian 09 program in B3LYP/6-311G*.

Hardware and software implementation of data acquisition system for pulsed NQR spectrometer

Abstract: A hardware and software implementation of compact data acquisition system for pulsed nuclear quadrupole resonance spectrometer is proposed The developed system is based on multi-protocol converter USB-245FIFO FT2232H, which provides data transfer speeds up to 480 Mb/s For nuclear spin induction visualization and data signal processing using graphical tools of the object oriented programming a Lab VIEW virtual instrument is synthesized The experimental results are showed possibility of the broadband nuclear quadrupole resonance spectrums imaging with frequency resolution 16 kHz, which confirms the high accuracy of the developed data acquisition system Two-channel transmitter provides simultaneous operation of the two independent data channels in a single hardware USB interface

75As-NQR Investigation of the Relationship between the Instability of Metal–Insulator Transition and Superconductivity in Ru1−xRhxAs

Abstract: We performed 75As nuclear quadrupole resonance (NQR) measurements on single-crystalline Ru1−xRhxAs to study the relationship between the superconductivity observed in a limited Rh-substitution regi...

Anisotropic Magnetic Fluctuations in Ferromagnetic Superconductor UGe2: 73Ge-NQR Study at Ambient Pressure

Abstract: We report a 73Ge nuclear quadrupole resonance reinvestigation of the ferromagnetic (FM) superconductor UGe2 at ambient pressure Careful measurement and analysis of the paramagnetic (PM) spectrum taking into account the calculated electric field gradient (EFG) resulted in modification of the previously reported site assignments for three inequivalent Ge sites The crossover anomaly at Tx in the FM state is not clearly seen in the temperature dependence of the static internal field at the Ge site, whereas it appears in the nuclear spin–lattice relaxation rate, 1/T1 A remarkable site dependence of 1/T1 is observed among the inequivalent Ge sites, where the directions of the principal axes of the EFG are different This result reveals that the magnetic fluctuation of UGe2 is highly anisotropic, which is consistent with the presence of Ising magnetic fluctuations in the PM state

Analysis of the Parameters of the Mössbauer Spectra and the Spectra of Nuclear Quadrupole Resonance of the Superconducting Ceramic YBa2Cu3O7

Abstract: The parameters of the Mossbauer spectra on 67Cu(67Zn), 67Ga(67Zn) isotopes, and the data of nuclear quadrupole resonance on an 17O isotope are anlayzed, and the lattice gradient of the electric field for the crystal lattice YBa2Cu3O7 is calculated. It is shown that these parameters correspond to the model when the hole is predominantly in the sublattice of the oxygen chain.

Application of a statically configured FPGA in the digital control system of the NQR radio spectrometer

Abstract: The digital control system of pulsed nuclear quadrupole resonance (NQR) Fourier radio spectrometer of laboratory type is developed, the main functional-algorithmic methods of which are implemented in field-programmable gate array (FPGA) Cyclone EP1C12F324. The algorithm of the proposed program and the configuration structure of the IC, created by means of the syntax of modeling the dynamic modes of logical structures on the basis of the finite state machine and functional modules, provide for the adjustment of all necessary NQR operation modes of the spectrometer and the operative control over the performance of the radiophysical experiment. The transfer of commands to the execution units of radiospectrometer at a rate of 3.15 Mbit/s is provided through a 4-bit parallel interface.

Nanoscale nuclear quadrupole resonance spectroscopy

Abstract: A method for probing the properties of nanoscale materials, such as 2D materials or proteins, via nanometer-scale nuclear quadrupole resonance (NQR) spectroscopy using individual atom-like impurities in diamond. Coherent manipulation of shallow nitrogen-vacancy (NV) color centers enables the probing of the NQR spectrum of nanoscale ensembles of nuclear spins. Measuring the NQR spectrum at different magnetic field orientations and magnitudes and fitting to a theoretical model allows for the extraction of atomic structural properties of the material with nanoscale resolution.

The adsorbtion of drug anti cancer melphalane on surface boron nitride nanotubes: a dft study

Abstract: In order to search for the interaction between Melphalane and nanotbe boron nitride is investigated using density functional theory (DFT). The structures of individual counterparts and hybrids have been optimized and the molecular properties have been evaluated. The Density of States (DOS) Plots, nuclear quadrupole resonance (NQR) analysisand nuclear magnetic resonance spectroscopy (NMR) are witness to the substantial changes in the electronic properties of pristine Nanotubes boron nitride systems following the attachment of the melphalane with the nanotubes surface.

Using a Spectrometer «Kazan-Nova II» to Identify Drugs by Nuclear Quadrupole Resonance

Abstract: The hardware-software complex based on the homebuild nuclear magnetic/quadrupole resonance spectrometer “Kazan-N ova II”, which allows to determine the authenticity of nitrogen-containing drugs by a nondestructive method is considered in the article. The possibility to distinguish the drugs from different manufacturers using their NQR spectra is shown, which makes it possible to use this device as a scanner of the authenticity of medicinal products, as well as for the formation of a database of reference spectra.

Nuclear quadrupole resonance detection system and antenna thereof

Abstract: The present solution relates to the technical field of application of nuclear quadrupole resonance (NQR) and geomagnetic field nuclear magnetic resonance systems, and provides an NQR detection system and an antenna thereof. The antenna comprises: a first coil Q1 which forms a first pattern; a second coil Q2 which forms a second pattern; and a gradient antenna composed of the first coil Q1 and the second coil Q2 and used for receiving radio-frequency interference from a target area signal and the outside, wherein the first coil and the second coil are located on the same plane, and the winding directions of the first coil Q1 and the second coil Q2 are opposite, the second pattern is evenly distributed around the first pattern, and the area of the first pattern is equal to the that of the second pattern. According to the present solution, the capacity of an antenna for suppressing radio interference in the environment when the antenna is used for detecting the NQR or applied to the ground magnetic resonance can be effectively improved. The signal detection capability is enhanced, so that the signal noise ratio of the system is improved.

NQR, NMR, and X-ray crystal structure studies of [4-C2H5-C6H4NH3]2MBr4 (M=Zn, Cd) B A journal of chemical sciences

Abstract: The crystal structure of [4-C₂H₅-C₆H₄NH₃]₂ZnBr₄ (1) has been determined at 150(2) K: triclinic, P1, a=724.82(2), b=1194.20(4), c=1322.26(4) pm, α=74.151(3), β=80.887(3), γ=80.434(3)°, and Z=2. There are two crystallographically independent cations in the unit cell of 1: one has its benzene ring perpendicular to the crystallographic a axis of the unit cell and the other one has its benzene ring perpendicular to the c axis. These cations are alternatingly located along the c axis and form organic layers, and the ZnBr₄ anions form inorganic layers in between. Zn–Br···H–N hydrogen bonds are formed between cations and anions. In accordance with the crystal structure, four nuclear quadrupole resonance (NQR) lines of ⁸¹Br were observed. The temperature dependence of the ⁸¹Br NQR frequencies between 77 and 320 K shows a peculiar feature which is not due to a structural phase transition. The measurement of ¹³C nuclear magnetic resonance spectra at around T=340 K indicates a redistribution of cations. The temperature dependence of ⁸¹Br NQR frequencies and differential thermal analysis measurements show that [4-C₂H₅-C₆H₄NH₃]₂CdBr₄ (2) undergoes a structural phase transition at around 190 K.