Showing papers on "Nuclear quadrupole resonance published in 1998"
TL;DR: In this article, the authors present a systematic NMR/NQR study of La 2CuO41d for a range of d, which demonstrates that the density of such sites increases with d.
Abstract: Copper NQR spectra demonstrate the existence of a second, anomalous copper site in lanthanum cuprate whose character is independent of the method of doping. We present a systematic NMR/NQR study of La 2CuO41d for a range of d, which demonstrates that the density of such sites increases with d. Analysis of our results and of published data from La 22xSr xCuO4 indicate that a substantial fraction of the doped holes in these materials localize in CuO 6 octahedra adjacent to the out-of-plane dopants, and that the anomalous sites are those neighboring a site occupied by such a pinned hole. Thus, superconductivity occurs in a CuO2 plane containing many localized holes. @S0163-1829~98!51702-X#
58 citations
Patent•
12 Jan 1998
TL;DR: In this article, the authors present an approach for testing a remote sample containing a given species of quadrupolar nucleus containing at least one probe (112) having a given maximum cross-sectional dimension.
Abstract: Apparatus for Nuclear Quadrupole Resonance testing a remote sample containing a given species of quadrupolar nucleus includes at least one probe (112) having a given maximum cross-sectional dimension; a device (102) for applying excitation to the probe or at least one of the probes to excite nuclear quadruple resonance for a selected range of distance of the sample from each such probe, the selected range being at least one tenth of the given maximum dimension of the probe, the apparatus being adapted to produce a non-uniform field over the selected range; and a device (106) for detecting the resonance response signal from the sample via the probe or at least one of the probes; the excitation being such as would generate non-zero resonance signals at all distances within the selected range.
58 citations
Patent•
06 May 1998
TL;DR: In this article, a spin-locked inversion mid-echo (SLIME) pulse sequence is used for the detection of explosives and drugs in a nuclear quadrupole resonance (NQR) system.
Abstract: A method and system for canceling extraneous signals in a nuclear quadrupole resonance (NQR) system used for the detection of explosives and drugs. A specimen is irradiated with a specific sequence of electromagnetic pulses, referred to as a spin-locked inversion mid-echo (SLIME) pulse sequence with each pulse having a specified phase and duration. The pulses are separated by specified time intervals. The SLIME pulse sequence has a single excitation pulse. As a result of the characteristics of the SLIME pulse sequence, if the target substance to be detected is present in the specimen, sets of oppositely-phased NQR echo signals are generated from the target substance. NQR echo signals of one phase are subtracted from NQR echo signals having the opposite phase, rendering a cumulative echo signal, and simultaneously subtracting out the same-phase extraneous signal.
48 citations
Patent•
17 Nov 1998TL;DR: In this article, a Nuclear Quadrupole Resonance (NQR) method and an apparatus for detecting the presence of a nitramine explosive, with a reduced probability of spurious triggering of consumer electronics, is presented.
Abstract: A Nuclear Quadrupole Resonance (NQR) method and apparatus for detecting the presence of a nitramine explosive, with a reduced probability of spurious triggering of consumer electronics. In the method and apparatus, a signal is emitted towards a nitramine explosive so that a nitro group in the namine explosive produces an NQR resonance signal. The NQR resonance signal is then detected to thereby detect the presence of the nitramine explosive. If the nitramine explosive is RDX, the NQR resonance signal of the nitro group is at a frequency which is either 502.3 kHz, 500.5 kHz, 405.1 kHz, 396.2 kHz or 384.1 kHz. Such frequencies are much lower than those in conventional detection techniques. As a result, the probability of the undesirable spurious triggering of electronic items exposed to the NQR RF pulses will be reduced, due to the reduction in induced voltage at lower frequency. The detection sensitivity is also reduced, but in many cases will still be adequate to detect nitramine explosives.
39 citations
TL;DR: In this article, modifications of the steady-state free-precession (SSFP) sequence are proposed for the effective detection of pure nuclear quadrupole resonance (NQR).
Abstract: Modifications of the steady-state free-precession (SSFP) sequence are proposed for the effective detection of pure nuclear quadrupole resonance (NQR). These modifications enable the suppression of the effect of intensity anomalies observed under steady-state conditions. The steady-state signals in SSFP-type sequences strongly depend on the frequency offset from resonance and the pulse spacing. This dependence has some peculiarities which were taken into consideration. Experimental results of modified SSFP sequence applications are reported for nitrogen-14 NQR in a plastic explosive.
32 citations
30 citations
TL;DR: It is shown that exact 31P lineshape calculations provide the relative signs of CQ, the isotropic J-coupling, and the effective dipolar coupling constant, which appears to be the first unambiguous determination of Delta1J(31P, 63/65Cu).
27 citations
TL;DR: In this article, the nuclear-spin lattice relaxation rate of CeRu 2 has been investigated using an NQR technique in zero magnetic field, and it is considered that the impurity scattering averages out the anisotropy of the energy gap.
Abstract: Superconducting characteristics of CeRu 2 have been investigated by systematic measurements of the nuclear-spin lattice relaxation rate, 1/ T 1 of 101 Ru on pure and impurity-substituted CeRu 2 , employing an NQR technique in zero magnetic field. (1/ T 1 ) for CeRu 2 shows a broad coherence plateau just below T c followed by an exponential decrease well below T c . By contrast, a distinct coherence peak of (1/ T 1 ) has been found just below T c for the impurity-substituted CeRu 2 , even though La- and Al-substitutions for the Ce and Ru sites make T c slightly increase and decrease, respectively. It is considered that the impurity scattering averages out the anisotropy of the energy gap, in good agreement with the theory of dirty superconductors by Anderson. 101 (1/ T 1 T ) in the normal state, which is in proportion to the square of the density of states at the Fermi level, N 2 ( E F ), is found to decrease with the Al content. The suppression in T c by substituting nonmagnetic Al impurity for the Ru sit...
26 citations
TL;DR: The structural behavior of zirconolite (CaZrTi2O7) under reducing conditions at high temperature has been studied, mainly by scanning electron microscopy (SEM) and x-ray diffraction (XRD), but also with xray absorption spectroscopy, thermogravimetry, and electron paramagnetic resonance as mentioned in this paper.
Abstract: The structural behavior of zirconolite (CaZrTi2O7) under reducing conditions at high temperature has been studied, mainly by scanning electron microscopy (SEM) and x-ray diffraction (XRD), but also with x-ray absorption spectroscopy, thermogravimetry, and electron paramagnetic resonance. The partial reduction of Ti4+ to Ti3+, associated with a reducing atmosphere heat treatment, led to the initial formation of perovskite (CaTiO3) as a second phase. As the concentration of Ti3+ in the zirconolite increased, so did the amount of perovskite until the zirconolite was totally transformed into a fluorite structured phase. Analysis of the reduced zirconolites showed them to be consistently deficient in Ca and enriched in Zr, in proportion to the concentration of Ti3+. To determine how electroneutrality was preserved in these reduced zirconolites, a series of zirconolites were prepared in air using In3+ and Ga3+ as models for Ti3+. These samples were then investigated by neutron and x-ray diffraction, SEM, solid state nuclear magnetic resonance (NMR), and nuclear quadrupole resonance (NQR). 71Ga MAS NMR studies of the Ga substituted zirconolite exhibited a narrow resonance at ˜13 ppm which was attributed to six-coordinate Ga incorporated in a trace perovskite phase. Broadline 71Ga NMR and 69/71Ga NQR were required to characterize the Ga incorporated in the zirconolite. The resultant quadrupolar parameters of CQ = 30.0 ± 0.05 MHz and η = 1.0 ± 0.03 indicate that the Ga site is in a highly distorted environment which would suggest that it is located on the five-coordinate Ti site within the zirconolite lattice. These results were complemented by Rietveld refinement of the neutron diffraction data from the In-doped zirconolite sample, which was optimal when all the In was located on the five-coordinate Ti site with the excess Zr located on the Ca site. It would therefore appear that charge compensation for the presence of Ti3+ in zirconolite is effected via the substitution of an appropriate amount of Zr on the Ca site. The Ti3+-stabilized fluorite structure was readily oxidized back to a single phase zirconolite upon heating in air.
24 citations
04 Sep 1998
TL;DR: In this paper, the authors reviewed the progress achieved under a recent initiative to detect landmines by nuclear quadrupole resonance (NQR) and reported the sensitivity of an NQR detection system to detect the electromagnetic response of metal-cased landmine.
Abstract: Nuclear Quadrupole Resonance (NQR) combines the compound specific detection capability offered by chemical detection techniques with the spatial localization capability and convenience of an induction coil metal detector. In the 16 years since NQR was last applied to mine detection in the U.S., there has been considerable improvement in the basic techniques. This paper reviews the progress achieved under a recent initiative to detect landmines by NQR. Two basic technical developments are summarized: the design of a detection coil suitable for probing the ground for landmines buried at typical depths, and an increase in the NQR signal obtained from the explosive TNT. In addition, we report the sensitivity of an NQR detection system to detect the electromagnetic response of metal-cased landmines.
24 citations
TL;DR: In this paper, the phenomena of hydrogen/water solubility in YBa2Cu3O7-δ and BaCeO3 undoped and doped by Y and Nd are considered.
Abstract: The phenomena of hydrogen/water solubility in YBa2Cu3O7-δ and BaCeO3 undoped and doped by Y and Nd are considered. New experimental data as well as recently published data have been accumulated to discuss the chemical state of protons, taking into account the fairly strong interaction of the protons with the electron subsystem. Phase transformation of the studied oxides induced by hydrogen/water intercalation were revealed by the investigations of thermal effects, X-ray diffraction, Raman spectroscopy, inelastic neutron scattering and nuclear quadrupole resonance.
TL;DR: Suh et al. as mentioned in this paper showed that the magnetic properties are remarkably insensitive to the character of the dopant impurity, which indicates that the added holes form previously unrecognized collective structures.
Abstract: V OLUME 81, N UMBER 13 PHYSICAL REVIEW LETTERS 28 S EPTEMBER 1998 Suppression of Antiferromagnetic Order by Light Hole Doping in La 2 Cu 12x Li x O 4 : A 139 La NQR Study B. J. Suh, 1 P. C. Hammel, 1 Y. Yoshinari, 1 J. D. Thompson, 1 J. L. Sarrao, 1 and Z. Fisk 2 Condensed Matter and Thermal Physics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306 ( Received 22 October 1997 ) La nuclear quadrupole resonance measurements in lightly doped La 2 Cu 12x Li x O 4 have been performed to reveal the dependence of the magnetic properties of the antiferromagnetic CuO 2 planes on the character of the doped holes and their interactions with the dopant. A detailed study shows that the magnetic properties are remarkably insensitive to the character of the dopant impurity. This indicates that the added holes form previously unrecognized collective structures. [S0031-9007(98)07260-3] PACS numbers: 75.30.Kz, 74.72.Dn, 76.60.Gv, 76.60.Jx Full understanding of the character of holes added to cuprate planes and their interactions with the two- dimensional lattice of Cu spins remains a crucial and un- solved problem in the high temperature superconductors. While the detailed mechanism is poorly understood, the rapid suppression of the antiferromagnetic (AF) ordering temperature T N by doping is clearly related to the disrup- tive effects of mobile holes: &3% added holes whether from Sr substitution, addition of interstitial oxygen, or in- plane substitution of Li for Cu [1] suppresses T N to zero, yet ,30% isovalent substitution of Zn or Mg for Cu is required [2] to produce the same effect. Li- and Sr-doped holes have very different mobilities. For x or y o 0.025, the room temperature resistivity r of La 2 Cu 12x Li x O 4 ex- ceeds that of La 22y Sr y CuO 4 by over an order of magni- tude [1,3,4]; more strikingly, for Sr doping drydT . 0 for T * 100 K, in contrast to the negative slope found in Li-doped material for all x and T . It is well recognized that the 2D cuprates are inclined to- ward microscopic charge inhomogeneity [5–7]. Evidence for such an effect in lightly doped La 22y Sr y CuO 4 was ob- tained from a scaling analysis of the doping y and tem- perature T dependence of the static susceptibility xs y, T d [8] which indicated that the magnetic correlation length is limited to the dimensions of AF domains (finite-size scal- ing) formed by microsegregation of doped holes into hole- rich domain walls surrounding hole-free, AF domains. Interpretations involving charge stripes have also been pro- posed [9]. Castro Neto and Hone [10] have examined the influence of doping on the long wavelength properties of a 2D antiferromagnet in a model in which charged stripes cause the exchange coupling J to become anisotropic; this model reproduces the relationship between M s 0 (M s is the sublattice magnetization; M s 0 is that obtained by extrapo- lation of data for T . 30 K to T 0) and T N as the two are suppressed by Sr doping in La 22y Sr y CuO 4 [11]. How- ever, using a similar model, van Duin and Zaanen [12] find that T N is suppressed much more rapidly than M s 0 with in- creasing anisotropy (doping). We have used 139 La nuclear quadrupole resonance (NQR) measurements to microscopically examine the 0031-9007y98y81(13)y2791(4)$15.00 effects of doped holes on the AF spin correlations in La 2 Cu 12x Li x O 4 s0.019 , x , 0.025d. We find that the magnetic behavior of lanthanum cuprate is remarkably insensitive to the detailed nature of the dopant, in spite of the differing charge transport associated with the two dopants. In addition to the similarly strong suppression of T N by doping, we find the identical correspondence between the suppression of M s 0 and T N by doping which has been observed in La 22y Sr y CuO 4 . Further we show, for the first time, that in the vicinity of T N the dynamical susceptibility, as reflected in the nuclear spin-lattice relax- ation rate 2W, follows a scaling law consistent with the finite-size scaling demonstrated in the static susceptibility by Cho et al. [8]. Finally, at low temperature, we find that two peculiar features are very similar in the two systems. These are the very strong peak in 2W (at a temperature T f 10 16 K depending on x) that indicates freezing of spin degrees of freedom, which is accompanied at slightly higher temperatures s. 30 Kd by the abrupt recovery of M s sT d, almost to x 0 values. Thus, while very small concentrations of added holes induce a range of characteristic magnetic properties which are entirely insensitive to the nature of the dopant, the transport properties are very sensitive to the dopant. Unable to understand these contrasting behaviors as arising from properties of individual holes, we conclude holes form collective structures. We will argue that holes form charged, antiphase domain walls [13] which surround mobile domains in which the phase of the AF order is reversed. Such mobile domains will suppress the time-averaged static moment thus suppressing AF order and M s . These domain structures will have contrasting interactions with in-plane vs out-of-plane dopants (e.g., stronger scattering by in-plane impurities) which explain the different transport behaviors, while the universal magnetic properties can be understood as long as the domains are sufficiently mobile that they move across a given site rapidly compared to a measurement time. Three powder samples of La 2 Cu 12x Li x O 4 (labeled A1, B1, and B2) were prepared from starting material con- taining concentrations x nom of Li as described elsewhere © 1998 The American Physical Society
TL;DR: In this article, a large number of solid fluoride and heteroligand acidocomplex compounds of antimony(III) and bismuth (III) with single and mixed cations have been prepared from aqueous solutions.
Abstract: Abstract A large number of solid fluoride and heteroligand acidocomplex compounds of antimony(III) and bismuth(III) with single and mixed cations has been prepared from aqueous solutions. Their crystal structures and 121,123Sb and 209Bi NQR spectra have been investigated in a wide temperature range.
TL;DR: The 7 F 0 → 5 D 0 transition in EuCl 3 6H 2 O is exceedingly narrow ∼0.5 GHz and exhibits partially resolved hyperfine splittings.
TL;DR: In this article, the qualitative and quantitative features of the electronic charge distribution in cuprate superconductors are reexamined on the basis of a comprehensive set of nuclear quadrupole resonance and NMR measurements.
Abstract: The qualitative and quantitative features of the electronic charge distribution in cuprate superconductors are reexamined on the basis of a comprehensive set of nuclear quadrupole resonance and NMR measurements. A systematic analysis of measured electric-field gradients is performed within the tight-binding approach, commonly used for electronic models in cuprates. Both in-plane and out-of-plane sites and orbitals are considered. Special attention is given to the generic pd model involving only the σ orbitals in the CuO2 planes. This model is checked against the experimental data. The physical origin of several material-dependent features is clarified. It is shown that in La2-xSrxCuO4 the 3d3z2-r2 orbital of the in-plane copper and the 2pz apex oxygen orbital are occupied by a substantially smaller fraction of holes than the in-plane σ orbitals, at variance with proposals lending importance to copper-apex oxygen hybridization. At the in-plane oxygen site a sizable 2pz admixture is found at the Fermi level of YBa2Cu3O7. The in-plane charge distribution of Tl2Ba2CuO4 is found to be qualitatively similar to that of the high-temperature tetragonal phase of La2-xSrxCuO4. It appears that the additional holes are shared among copper and oxygen sites in similar proportions. This is shown to be compatible with the large Ud Emery model provided that the difference between the p and d atomic energies is comparable to the first neighbor overlap energy.
TL;DR: Pulsed 75 As nuclear quadrupole resonance (NQR) experiments performed on rapidly drawn (>100 m/min) fibers of As2Se3 reveal structure which differs from the bulk, well-annealed glass as mentioned in this paper.
Abstract: Pulsed 75 As nuclear quadrupole resonance (NQR) experiments performed on rapidly-drawn (>100 m/min) fibers of As2Se3 reveal structure which differs from the bulk, well-annealed glass. In addition to the presence of As–As bonds in the nominally stoichiometric fibers, a distorted `crystalline' phase occurs at the greatest draw rates. Like the Ge–Se–S system, this phase probably involves more ordered local molecular clusters whose sizes are not yet well-determined. Because these crystalline regions are highly distorted compared to bulk, crystalline As2Se3, they are not observable by X-ray spectroscopy except in a few cases. On the other hand, the NQR experiments show the presence of crystalline regions. In all cases, the crystalline phase makes up less than 5% of the volume. In addition to being strained, the imbedded crystallites partially `anneal' to the amorphous phase over time when stored at 300 K. This annealing behavior is similar to that which exists in the Ge–Se–S system, but different from the `photo-induced amorphization' recently reported for evaporated AsSe films.
TL;DR: In this article, the temperature dependence of the proton order parameter is derived from the NQR data and the energy difference Δ E of the two equilibrium proton configurations is calculated.
TL;DR: In this paper, the dispersion of brominated flame retardants in polymers is monitored with 81Br nuclear quadrupole resonance (NQR) using a pulse NQR spectrometer.
Abstract: The dispersion of brominated flame retardants in polymers is monitored with 81Br nuclear quadrupole resonance (NQR) using a pulse NQR spectrometer. The NQR spectrometer consists of a homemade 10−300 MHz single-channel NMR console coupled to a broadly tunable probe. The probe is a loop−gap resonator usable from 220 to 300 MHz and is automatically tuned over any 5 MHz region with a stepping motor and a radio frequency bidirectional coupler. 81Br NQR spectra of several brominated aromatic flame retardants, as pure materials and in polymers, were recorded in the range of 227 to 256 MHz in zero applied magnetic field. Two factors affect the 79/81Br NQR transition frequencies in brominated aromatics: electron-withdrawing substituents on the ring and intermolecular contacts with other bromine atoms in the crystal structure. An existing model for substituents is updated, and a point charge model for the intermolecular contacts is developed. In this study, we exploit the 81Br NQR transition frequency dependence o...
TL;DR: In this article, the second order normal-incommensurate transition at Ti = 224 K is accompanied by the symmetry change P6 3 mmc ↔ P2 1 m, and the transition into a ferroelastic incommensurate phase occurs at the zone center.
TL;DR: In this paper, the nuclear quadrupole resonance (NQR) of 35Cl was measured at room temperature in molecular alloys of PDClB(1 − x)PDBrB(x) as a function of the concentration x expressed as a molar fraction of PDBrB.
Patent•
15 Oct 1998
TL;DR: In this article, the off-resonance and sensitivity of the NQR test may be further improved by applying excitation (in the form of "bridging pulses") between the two excitation blocks.
Abstract: Methods of and apparatus for Nuclear Quadrupole Resonance (NQR) testing a sample containing quadrupolar nuclei exhibiting a given value of spin-lattice relaxation time, T1, are disclosed. The off-resonance and the sensitivity of the NQR test may be futher improved by applying excitation (in the form of 'bridging pulses') between the two excitation blocks. The method comprises applying two excitation blocks to excite nuclear quadrupole resonance, there being a given delay time between the two blocks, detecting resonance response signals, and comparing the response signals from respective blocks. The delay time is less than the T1 value of the nuclei.
TL;DR: In this article, the broad spectra in the incommensurate phase of bis~4-chlorophenyl! sulfone were measured using the Fourier transform of the nuclear signal to avoid systematic errors committed in some studies of this compound.
Abstract: In this work, previous experimental studies of the Cl nuclear-quadrupole-resonance ~NQR! line shape in the incommensurate phase of bis~4-chlorophenyl! sulfone were extended. The broad spectra in the incommensurate phase ~IC! were measured using the Fourier transform of the nuclear signal to avoid systematic errors committed in some studies of this compound. The results were interpreted within the framework of the general treatment developed by Perez-Mato, Walisch, and Petersson. The effects of the incommensurate modulation on the asymmetry parameter of the electric-field gradient were explicitly included in the expression of the NQR frequency. The features of the spectra were adequately reproduced in the whole temperature range, by considering the nonsinusoidal character of the atomic modulations reported by x-ray diffraction. No evidences were found concerning IC wave fluctuations smearing out the singularities of the NQR spectrum. On the other hand, relative intensity of NQR peaks and temperature behavior of some parameters of the plane-wave ‘‘local’’ model were explicitly calculated. Comparison of these quantities with the experimental results excludes the applicability of the ‘‘local’’ model in the case of bis~4-chlorophenyl! sulfone. @S0163-1829~98!06006-8#
TL;DR: In this article, a phase-modulated version of the nutation spectroscopy was applied to a quadrupolar nucleus at zero field, where the first period is the duration of the radio frequency exciting pulse and the second dimension is the free-evolution period of the nucleus.
Abstract: Nutation nuclear quadrupole resonance spectroscopy enables one to determine the asymmetry parameter on powder samples. The method relies on two-dimensional methodology: The first period is the duration of the radio frequency exciting pulse and the second dimension is the free-evolution period of the quadrupolar nucleus. Varying lengths of the radio frequency pulse induce an amplitude modulation of the free-induction decay signals which is characteristic of the anisotropic nutation frequency distribution. Fourier analysis along the first dimension provides a powder nutation line shape that allows determination of the electric field gradient tensor’s asymmetry parameter. We describe the first application of two-dimensional phase-modulated spectroscopy to a quadrupolar nucleus at zero field. It is shown that a phase-modulated variant of the nutation spectroscopy is feasible in the pure quadrupole regime and it provides a gain in the signal-to-noise ratio compared to the amplitude-modulated method.
TL;DR: In this paper, the use of first-order and second-order quadrupolar effects in B NMR spectra to obtain structural information, and B and B NQR spectra were used to obtain the quadrupol parameters Qcc (the coupling constant) and (the asymmetry parameter) with accuracies of 5 or 6 significant figures, and 3 figures, respectively.
Abstract: Nuclear magnetic resonance (NMR) has been used for some 40 years to study atomic arrangements, chemical bonding, and structural groupings in borate glasses and crystalline compounds, and nuclear quadrupole resonance (NQR) has more recently increased the resolution and accuracy of the measurements. Examples are presented of the use of first-order and second-order quadrupolar effects in B NMR spectra to obtain structural information, andB and B NQR spectra to obtain the quadrupolar parameters Qcc (the coupling constant) and (the asymmetry parameter) with accuracies of 5 or 6 significant figures, and 3 figures, respectively. Qcc and are extremely sensitive to changes in atomic rearrangements and chemical bonds, so they are excellent monitors and provide identification of bonding configurations and structural groupings in borates: Examples are also presented in which combinations of NMR and NQR data are used to extract the desired information. NQR detection of resonances at frequencies as low as 276 kHz is discussed.
TL;DR: In this article, the authors compared the experimental and theoretical magnitudes of the electric field gradient at nuclear sites in powder samples of semimetallic arsenic and antimony using pulsed nuclear quadrupole resonance to measure the nuclear resonance frequency.
Abstract: The pressure variation of the electric-field gradient (efg) at nuclear sites in powder samples of semimetallic arsenic and antimony has been investigated up to 2.0 GPa at 293 K using pulsed nuclear quadrupole resonance to measure the nuclear resonance frequency. Theoretical calculations of both the total efg and the ionic contributions have been carried out. Full-potential linearized augmented plane wave (FLAPW) calculations of the total efg give values that are approximately 70% of the measured efg. The comparison between experimental and theoretical magnitudes of the efg is, however, to some extent limited by the accuracy of the values used for the quadrupole moments of ${}^{75}\mathrm{As}$ and ${}^{121}\mathrm{Sb}.$ Additional uncertainties arise from the pressure dependence of the lattice parameters. FLAPW calculations of the dependence of the internal z parameter on the $c/a$ ratio suggest an inconsistency in available data for the pressure dependence of the lattice parameters. This inconsistency is particularly marked in the arsenic case, where very little high-pressure data are available. In the antimony case, our FLAPW estimate of the relative pressure variation of the efg at the nuclear sites, using experimentally determined lattice parameters, shows good agreement with the nuclear quadrupole resonance measurements. The pressure variation of the efg in arsenic is well reproduced by the FLAPW calculation when the experimental $c/a$ ratio and theoretically estimated z parameter are used.
TL;DR: In this paper, coherent Raman spectroscopy was applied for an optical-rf double-resonance study of a crystal doped with a nuclear spin Raman scattering.
Abstract: Coherent Raman spectroscopy was applied for an optical-rf double-resonance study of a ${\mathrm{LaF}}_{3}$ crystal doped with ${\mathrm{Pr}}^{3+}.$ The coherent nuclear spin Raman scattering was detected as a function of the applied rf frequency. Exciting the resonance condition of the ${}^{3}{\stackrel{\ensuremath{\rightarrow}}{{H}_{4}}}^{3}{P}_{0}$ transition of ${\mathrm{Pr}}^{3+}$ (20 925 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$), only the La nuclei surrounding the ${\mathrm{Pr}}^{3+}$ ion were observed through their nuclear quadrupole resonance (NQR). The double resonance between the optical transition of the ion and the NQR transition of its neighboring nucleus is theoretically described by analyzing the magnetic dipolar interaction that is affected by the optical excitation. Under a certain restriction, which the present system fulfills, the intensity of the Raman heterodyne signal can be described by an analytical function of the internuclear vector and the orientation of the electric-field gradient (EFG) at the Pr and La nuclei. Five different neighboring La nuclei were observed. They are different from the bulk La in both magnitude and orientation of the EFG. In addition, it was found that the laser frequency jitter affects the relative signal intensity of the different La NQR transitions through the optical pumping of the La spin levels.
TL;DR: In this article, a multiresolution analysis of experimentally observed NQR signatures for RDX response and various false alarm signatures in the absence of explosive compounds was performed under DARPA sponsorship.
Abstract: Nuclear Quadrupole Resonance (NQR) is effective for the detecting and identification of certain types of explosives such as RDX, PETN and TNT. In explosive detection, the NQR response of certain 14N nuclei present in the crystalline material is proved. The 14N nuclei possess a nuclear quadrupole moment which in the presence of an electric field gradient produces an energy level splitting which may be excited by radio-frequency magnetic fields. Pulsing on the sample with a radio signal of the appropriate frequency produces a transient NQR response which may then be detected. Since the resonant frequency is dependent upon both the quadrupole moment of the 14N nucleus and the nature of the local electric field gradients, it is very compound specific. Under DARPA sponsorship, the authors are using multiresolution methods to investigate the enhancement of operation of NQR explosives detectors used for mine detection. For this application, NQR processing time must be reduced to less than one second. False alarm response due to acoustic and piezoelectric ringing must be suppressed. Also, as TNT is the most prevalent explosive found in land mines NWR detection of TNT must be made practical despite unfavorable relaxation times. All three issues require improvement in signal-to-noise ratio, and all would benefit from improved feature extraction. This paper reports some of the insights provided by multiresolution methods that can be used to obtain these improvements. It includes results of multiresolution analysis of experimentally observed NQR signatures for RDX response and various false alarm signatures in the absence of explosive compounds.
TL;DR: In this paper, the asymmetry parameter of the EFG tensor from zero-field nutation NQR spectra of the spinI = 3/2 nuclei in powder samples was determined from the second and fourth spectrum moments alone.
Abstract: A novel approach to determination of the asymmetry parameter of the EFG tensor from zero-field nutation NQR spectra of the spinI = 3/2 nuclei in powder samples is reported. The proposed theoretical treatment uses lineshape analysis of the nutation NQR spectra by the method of line moments. The analytical formulas for the lineshape of the powder nutation spectrum are given. It is shown that the asymmetry parameter can be determined from the second moment 〈ω2〉 and the frequency of only one singularity ω2 of the nutation spectrum. It is also shown that the asymmetry parameter can be determined from the second and fourth spectrum moments alone. The method is successfully demonstrated for the simulated nutation NQR spectra of the spinI = 3/2 nuclei in powder samples.
TL;DR: Meersmann and Haake as discussed by the authors confirmed that the recently discovered field-dependent nuclear quadrupolar splitting of 131Xe arises from a distortion of the electron density due to the applied magnetic field, which depends both linearly and quadratically on the applied field.
Abstract: We confirm that the recently discovered field-dependent nuclear quadrupolar splitting of 131Xe [T. Meersmann and M. Haake, Phys. Rev. Lett. 81, 1211 (1998)] arises from a distortion of the electron density due to the applied magnetic field. This distortion depends both linearly and quadratically on the applied field. The existence of the former is due to the coupling to the field and the nuclear spin. The latter is a manifestation of the quadratic Zeeman effect. In addition to confirming the order of magnitude for the observed effect, we show that there should be an asymmetry introduced in the spectra due to the linear coupling with the nuclear spin. This effect has not been seen experimentally.
TL;DR: In this paper, the role of Br in reoxygenating the YBCO structure and an explanation for the partial restoration of superconductivity in the yBa2Cu3Oy (YBCO) system was investigated.
Abstract: 63,65Cu nuclear quadrupole resonance (NQR) and Br k-edge x-ray absorption fine structure (XAFS) have been used to study the local structures in well-characterized samples of deoxygenated and brominated YBa2Cu3Oy(YBCO). NQR shows that after bromination of YBa2Cu3O6.1 at 260 °C, oxygen has repopulated the chain sites. From XAFS, it is concluded that Br does not enter the YBCO lattice, but rather precipitates out as small nanoscale particles of BaBr2. These results provide clear evidence of the role of Br in reoxygenating the YBCO structure and an explanation for the partial restoration of superconductivity in the YBCO system.