Nuclear Quadruple Resonance Research Articles

Nuclear giant quadruple resonance within a transport approach and its constraint on the nucleon effective mass

We study the nuclear iso-scalar giant quadruple resonance~(ISGQR) based on the Boltzmann-Uehling-Uhlenbeck~(BUU) transport equation. The mean-field part of the BUU equation is described by the Skyrme nucleon-nucleon effective interaction, and its collision term, which embodies the two-particle-two-hole ($2$p-$2$h) correlation, is implemented through the stochastic approach. We find that the width of ISGQR for heavy nuclei is exhausted dominated by collisional damping, which is incorporated into the BUU equation through its collision term, and it can be well reproduced through employing a proper in-medium nucleon-nucleon cross section. Based on further Vlasov and BUU calculations with a number of representative Skyrme interactions, the iso-scalar nucleon effective mass at saturation density is extracted respectively as $m^{*}_{s,0}/m$ $=$ $0.83\pm0.04$ and $m^{*}_{s,0}/m$ $=$ $0.82\pm0.03$ from the measured excitation energy $E_x$ of the ISGQR of $\isotope[208]{Pb}$. The small discrepancy between the two constraints indicates the negligible role of $2$p-$2$h correlation in constraining $m_{s,0}^*$ with the ISGQR excitation energy.

35Cl NQR Relaxation of the Molecular Ferroelectric 5,6-Dichloro-2-Methylbenzimidazole with Hydrogen-Bonded Molecular Chain

The 35Cl nuclear quadruple resonance (NQR) frequencies and spin-lattice relaxation times were measured in the temperature range of 4.2–420 K, of the above-room-temperature ferroelectric 5,6-dichloro-2-methylbenzimidazole, the ferroelectricity of which is thought to arise from the positional ordering of protons along chain of N-H...N hydrogen bonds. The first-order phase transition was clearly detected at around 400 K, as a discontinuity in the temperature dependence of NQR frequencies. The two NQR lines observed showed a much more significant difference in frequency in the high-temperature phase. This is consistent with the recently reported symmetry-lowering of crystal structure on warming. The relaxation mechanism in the low-temperature phase is discussed.

Detection of quasi-harmonic signals with a priori unknown parameters in strong additive noise by machine learning methods

Signals with a priori unknown parameters in strong noise are used in various fields of science and technology. This paper is devoted by features and limits deep neural networks for signal detection. We study quasi-harmonic signals with a priori unknown parameters. Neural network method was compared with classical methods for detecting signals in terms of accuracy and speed. We use realistic models of hexogen nuclear quadruple resonance (NQR) signals with parameters dependence by temperature. Experiments show that proposed method is more accurate and one hundred times faster than alternative ones. We achieve a probability of NQR signal detection about 95%, when signal-to-noise ratio is -15 dB and the signal parameters are unknown. When the signal-to-noise ratio is -20 dB, probability of NQR signal detection is 80%.

Machine learning in NQR TNT express detection system.

Nuclear quadruple resonance (NQR) has excellent potential for the remote detection of nitrogen-containing substances, such as trinitrotoluene (TNT). However, using NQR techniques in security systems have some problems. For example, unknown temperature of the detecting explosives and low signal-to-noise ratio (SNR) leads to a priori uncertainty of the parameters of the NQR signal. In the article, we use machine learning methods for detecting the NQR signal. It allows us to increase speed and accuracy of TNT NQR signal detection. We have shown that proposed method of NQR signal detecting is more accurate and 100 times faster than alternative methods if temperature uncertainty is above 10 degrees. We achieve probability of NQR signal detection about 95% for SNR -15 dB.

NMR evidence of charge fluctuations in multiferroic CuBr2**Project supported by the Ministry of Science and Technology of China (Grant No. 2016YFA0300504), the National Natural Science Foundation of China (Grant No. 11374364), the Fundamental Research Funds for the Central Universities of China, and the Research Funds of Renmin University, China (Grant No. 14XNLF08).

We report combined magnetic susceptibility, dielectric constant, nuclear quadruple resonance (NQR), and zero-field nuclear magnetic resonance (NMR) measurements on single crystals of multiferroics CuBr2. High quality of the sample is demonstrated by the sharp magnetic and magnetic-driven ferroelectric transition at 74 K. The zero-field 79Br and 81Br NMR are resolved below TN. The spin-lattice relaxation rates reveal charge fluctuations when cooled below 60 K. Evidences of an increase of NMR linewidth, a reduction of dielectric constant, and an increase of magnetic susceptibility are also seen at low temperatures. These data suggest an emergent instability which competes with the spiral magnetic ordering and the ferroelectricity. Candidate mechanisms are discussed based on the quasi-one-dimensional nature of the magnetic system.

An ab initio study on 3,4-methylenedioxymethamphetamine, MDMA (ecstasy) and its derivatives

Computational studies have been carried out at DFT-B3LYP/6-31+G* and PW91P86/6-31+G* levels of theory on the structural and spectroscopic properties of 3,4-methylenedioxymethamphetamine (MDMA) and its derivatives. Nuclear quadrupole coupling constants (NQCCs) of 14N and 17O and chemical shift of 13C and 1H have been calculated. There is a good correlation between the calculated chemical shifts of 13C and 1H and experimental data. Our results showed that 14N and 17O NQCCs are quite sensitive to substitute-induced structural charge. In these compounds, a correlation has been observed between the parameters characteristic biological activity (LD50, IC50) and nuclear quadruple resonance (NQR) parameters. We also report a computational study for the 14N and 17O nuclear magnetic resonance (NMR) tensors in ecstasy and its derivatives. To our knowledge, no sufficient ab initio study has been carried out on MDMA and its derivatives.

A Low-Power Compact NQR Based Explosive Detection System

Nuclear quadruple resonance (NQR) has been studied for explosive detection for years. Some prototype NQR-based detection systems have been reported, but were all designed from the laboratory perspective, with bulky sizes and high power consumption. To achieve a portable NQR-based detection system for field applications, a low-power compact system utilizing state-of-the-art semiconductor technologies is presented in this paper. Several novel circuits for the key modules are proposed, including a Class-D type power amplifier, a power multiplexing and matching network, a customized IC with integrated analog signal processing chain, and a microcontroller-based logic control unit. An advanced digital signal processor platform is employed for data collecting and processing. The customized IC is fabricated in 0.18 μm CMOS process. Test results on the prototype system show the effectiveness of the proposed solution and low power consumption as 2.12 W in the receiving state. The power efficiency of the proposed transmitting section is higher than 60%.

Explosive Detection – An Integrated Technique

The increased pressure of terrorist action have led to the invention of many new and spectacular techniques for the detection of concealed weapon and explosives. These include trace detection systems for the detection of vapors or particles of explosive left behind during carrying, nuclear quadruple resonance, neutron activation, X ray scanner and other systems based on energetic radiation. But these are all traditional methods which has more limitations in the detection. Emerging of Advanced ground sensors (embedded system), remote sensing and GIS techniques with the support of highly advanced image processing software enable many new ideologies to detect the explosives with higher accuracy. So we incorporated active and passive system to detect the explosives. This integrated technique will work successfully by employing this proposed technique at the border of our nation especially in the coastal area. Since the unavailability of data (which is required to be sensed on the day when explosion taken place), only the methodology and techniques are discussed in this study.

Potential Antiferromagnetic Fluctuations in Hole-Doped Iron-Pnictide Superconductor Ba1-xKxFe2As2 Studied by 75As Nuclear Magnetic Resonance Measurement

We have performed 75 As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on single-crystalline Ba 1- x K x Fe 2 As 2 for x = 0.27–1. 75 As nuclear quadruple resonance frequency (ν Q ) increases linearly with increasing x . The Knight shift K in the normal state shows Pauli paramagnetic behavior with a weak temperature T dependence. K increases gradually with increasing x . By contrast, the nuclear spin–lattice relaxation rate 1/ T 1 in the normal state has a strong T dependence, which indicates the existence of large antiferomagnetic (AF) spin fluctuations for all x 's. The T dependence of 1/ T 1 shows a gaplike behavior below approximately 100 K for 0.6 < x < 0.9. This behaviors is well explained by the change in the band structure with the expansion of hole Fermi surfaces and the shrinkage and disappearance of electron Fermi surfaces at the Brillouin zone (BZ) with increasing x . The anisotropy of 1/ T 1 , represented by the ratio of 1/ T 1 a b to 1/ T 1 c , is always larger than 1 for all x 's, which indicates that stripe-type AF fluctuations are dominant in this system. The K in the superconducting (SC) state decreases, which corresponds to the appearance of spin-singlet superconductivity. The T dependence of 1/ T 1 in the SC state indicates a multiple-SC-gap feature. A simple two-gap model analysis shows that the larger superconducting gap gradually decreases with increasing x from 0.27 to 1 and a smaller gap decreases rapidly and nearly vanishes for x > 0.6 where electron pockets in BZ disappear.

Progress in methods for the identification of explosives in Russia

The progress in analytical methods for the determination of explosive done by Russian scientists is reviewed: gas analytical; nuclear physical, including neutron activation analysis; nuclear quadruple resonance (NQR); and optical spectroscopy.

F-doping dependence of 75As nuclear quadrupole resonance frequency in LaFeAs(O1−xFx)

We report the F-doping dependence of 75As nuclear quadruple resonance frequency (75νQ) in the iron-oxypnictide LaFeAs(O1−xFx) (x=0, 0.07, 0.08, 0.11 and 0.14). It was revealed that 75νQ becomes larger with increasing x up to 0.14. From point charge calculations, we found that experimental F-doping dependence of 75νQ cannot be accounted for by the effect of surrounding ions. Therefore, the on-site charge distribution at the 75As site modified by the hybridization between As-4p and Fe-3d orbitals gives dominant contribution to 75νQ in LaFeAs(O1−xFx).

Electronic structure of boron-doped diamond with B–H complex and B pair

The electronic structure of boron–hydrogen complex and boron pair in diamond are studied by first-principles density-functional calculations with supercell models. The electronic structure calculated for the B–H complexes with C2v or C3v symmetry and the nearest-neighbor B pair is used to interpret recent experimental results such as B 1s x-ray photoemission spectroscopy, 11B nuclear quadruple resonance and B K-edge x-ray absorption spectroscopy, which cannot be explained solely by the isolated substitutional boron.

Automated Nuclear Quadruple Resonance Spectrometer

Improvement of an autodyne Nuclear quadruple resonance spectrometer is offered. The change of frequency of oscillatory LC circuit of the spectrometer is carried out in two ways: by varic ...

Theoretical investigation of hydrogen bonding effects on oxygen, nitrogen, and hydrogen chemical shielding and electric field gradient tensors of chitosan/HI salt

A density functional theory study has been carried out to calculate the 17O, 15N, 13C, and 1H chemical shielding as well as 17O, 14N, and 2H electric field gradient tensors of chitosan/HI type I salt. These calculations were performed using the B3LYP functional and 6-311++G (d,p) and 6-31++G (d,p) basis sets. Calculated EFG and chemical shielding tensors were used to evaluate the 17O, 14N, and 2H nuclear quadruple resonance, NQR, and 17O, 15N, 13C, and 1H nuclear magnetic resonance, NMR, parameters in the cluster model, which are in good agreement with the available experimental data. The difference in the isotropic shielding ( σ iso) and quadrupole coupling constant ( C Q) between monomer and target molecule in the cluster was analyzed in detail. It was shown that both EFG and CS tensors are sensitive to hydrogen-bonding interactions, and calculating both tensors is an advantage. A different influence of various hydrogen bond types, N–H⋯I, O–H⋯I, and N–H⋯O was observed on the calculated CS and EFG tensors. On the basis of this study, nitrogen and O-6 are the most important nuclei to confirm crystalline structure of chitosan/HI. These nuclei have large change in their CS and EFG tensors because of forming intermolecular hydrogen bonds. Moreover, the quantum chemical calculations indicated that the intermolecular hydrogen-bonding interactions play an essential role in determining the relative orientation of CS and EFG tensors of O-6 and nitrogen atoms in the molecular frame axes.

Pseudo-spin-gap of (Y,Ca)(Ba,La) 2Cu 4O 8

The temperature dependence of Cu nuclear spin-lattice relaxation rate ( T 1 T) −1 and frequency spectra have been measured in Y 1− x Ca x Ba 2Cu 4O 8 ( x=0, 0.05 and 0.075) and YBa 2− y La y Cu 4O 8 ( y=0.05) by a zero field Cu nuclear quadruple resonance (NQR) spin-echo technique. The carrier doping dependence of pseudo-spin-gap was observed through ( T 1 T) −1 at the planar Cu site but no appreciable change in ( T 1 T) −1 at the chain site Cu. Cation substitution without oxygen deficiency is demonstrated to result in substantial carrier doping on the CuO 2 plane.

Electron Nuclear Quadruple Resonance for Assignment of Overlapping Spectra

Multiple resonance methods are important tools in EPR for revealing the network of hyperfine levels of free radicals and paramagnetic centers. The variations of electron nuclear double resonance (ENDOR) or electron spin-echo envelope modulation (ESEEM) techniques help to correlate nuclear frequencies with each other. These methods have limited utility when there is extensive overlap or suspected overlap in the EPR spectrum between different species or different orientations. In the ENDOR spectrum, overlap and second-order shifts of lines also leads to ambiguity in assignment and interpretation. A new electron nuclear multiple resonance method is presented here that is based on population transfer ENDOR. It is a quadruple resonance method that correlates ENDOR lines and reveals the network of hyperfine levels in samples with unoriented paramagnetic species and in samples with overlapping EPR or ENDOR lines.

Vibrational spectra and lattice dynamics of hydrogen-bonded NH4IO3 crystal in the pretransition region

The ferroelectric crystal of ammonium iodate NH4IO3 was investigated by the methods of Raman and IR spectroscopy. Powder IR and Raman temperature dependent spectra of the title crystal were measured in the temperature range 300–400K near the Curie temperature (Tc=367K). The 127I nuclear quadruple resonance (NQR) spectra of the NH4IO3 crystal, which were measured in the same temperature range, are discussed. The effect of hindered rotation of NH4+ and IO3− ions was revealed in the pretransition temperature range and is explained by anomalous crystal thermal expansion.

The dynamics of the NO 2 group in the solid phase of m-chloronitrobenzene studied by Raman spectroscopy and 35Cl NQR

Low-frequency Raman spectroscopy was used in order to characterize the interaction potential for the torsion of the nitro group in solid m-Cl-nitrobenzene. Lattice dynamics calculations considering a semirigid molecule enabled, for the first time, the identification of the torsional vibrations of the nitro group in the range 106–115 cm −1 at 295 K. On the other hand, from 35Cl nuclear quadruple resonance spin-lattice relaxation time data, a low limit for the reorientational barrier height of the nitro group could be determined. A simple calculation leads to an estimation of the intermolecular contribution to the reorientational barrier. It can be shown that this interaction dominates over the intramolecular one in fixing the potential barrier height.

Electric-field-gradient-tensor study in YBa2Cu3O7- delta high-Tc superconductors.

Electric-field-gradient-- (EFG-) tensor components, at all the nine nonequivalent sites in the unit cell of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ superconductors have been calculated on the basis of the point-charge model. ${V}_{\mathrm{zz}}$, the principal EFG components and \ensuremath{\eta}, the asymmetry parameters at two nonequivalent Cu sites, have also been evaluated as a function of \ensuremath{\delta}. The data reveal several new features of the EFG components in these superconductors and provides a new interpretation for the recently reported M\ossbauer and nuclear quadruple resonance spectroscopic results.

Nuclear quadrupole resonance spectroscopy. Part two. Instruments

This article is concerned with recent developments in the kinds of instrument that can be used to detect and record nuclear quadruple resonance signals in the solid state.