Non-cyclic geometric phase of nuclear quadrupole resonance signals of powdered samples

The non-cyclic geometric phase of ¹⁴N and ³⁵Cl NQR signals induced by the character of trajectory of nuclear magnetization motion upon pulse r.f. excitation of powdered samples is studied. Analytical expressions for the geometric phases of NQR signals of the nuclei of spins I=1 and 3/2 upon nuclear magnetization rotation induced by means of r.f. pulses with frequency detuned from the resonance and for any impulse duration for a separate crystallite are obtained. It is shown that the geometric phase recorded for the signal from a powdered sample at Δω=0 can be different from zero and can oscillate upon changes in duration of the r.f. excitation pulse. An alternative variant of the nutation experiment aimed at obtaining the asymmetry parameter η from locations of frequency singularities in the nutation phase spectrum for nuclei of spin I=3/2 in powder substances is proposed.     

Remote detection of double nuclear quadrupole resonance spectra

Remote detection of the spectra of double nuclear quadrupole resonance of nitrogen-containing compounds is considered. A comparison is made of this technique with the cross-relaxation method.     

Raman spectra from oblique phonons in powdered samples

We examined both experimentally and theoretically the Raman spectra from powder and polycrystalline samples of a crystal where mixing of pure modes is allowed. The theoretical and experimental spectra of LiIO₃ powder match perfectly, though little coincidence with the single crystal spectrum is obtained.     

Methods of spectral estimation in local nuclear quadrupole resonance with a dispersion

The spectral estimation in local nuclear quadrupole resonance at a high noise level is performed for the first time using the modern techniques of linear prediction (LPSVD) and matrix pencil (ITMPM). The fast Fourier transform with signal accumulation does not ensure the required sensitivity in the case of weak signals when the object and the receiver of the spectrometer are spaced widely apart or when there is an effect of adverse factors (screening, interference, random disturbance, etc.), which is typical of remote monitoring in actual practice. It is demonstrated that the use of the proposed techniques considerably increases the efficiency of spectral estimation in this field of solid-state spectroscopy and, in particular, avoids the phase errors arising in usual experiments at a signal-to-noise ratio of less than 0.5.     

Emission of nuclear quadrupole resonance from polycrystalline hexamethylenetetramine

The angular dependence of the nuclear quadrupole resonance (NQR) signal intensity emitted from polycrystalline hexamethylenetetramine has been analytically investigated for all directions for non-contact detection of chemicals by nuclear quadrupole resonance. The field pattern of the NQR signal from a column sample was measured. The emitted patterns were the same as that from a united single magnetic dipole, which fitted well to the estimation based on quadrupole principle axis system. This result is helpful to design an antenna for NQR remote detection.     

Diffusion in nuclear quadrupole resonance

With the aid of the method of random trajectories, formulas have been obtained for the first time for diffusion damping of the amplitudes of nuclear quadrupole spin echo signals because of molecular vibration-rotation in a two-frequency four-pulse program for spin 5/2 and zero asymmetry parameter. The formulas are similar to the result of Hahn for diffusion in NMR.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 14–16, June, 1985.     

The 10B and 11B nuclear quadrupole resonance spectra of boric acid

The ¹¹B and ¹⁰B nuclear quadrupole resonance spectra of boric acid have been obtained at 77 K, by means of the technique of double resonance by level crossing. A 92% ¹⁰B-enriched material was examined in addition to one of normal isotopic composition. The quadrupole coupling constant and asymmetry parameter for ¹⁰B are 5344(2) kHz and 0.0163(5), respectively. The corresponding quadrupole coupling constant for ¹¹B, assuming η = 0.0163, is 2576(8) kHz. The ¹⁰B spectrum is characterized by the appearance of transitions that may be classified as “multiple quantum,” in addition to the more highly allowed “single-quantum” transitions. Certain of these, which lie at frequencies higher than that of the one allowed ¹¹B transition, are useful in determining the field gradient parameters. In addition “double transitions,” corresponding to simultaneous changes in spin states at two dipolar-coupled nuclei, have been observed; these involve both ¹⁰B and ¹¹B.     

N nuclear quadrupole resonance in the barbiturates

The ¹⁴N nuclear quadrupole resonance frequencies at 77 K are reported for several barbiturates. Differences between charge densities in the π and various σ orbitals at the nitrogen site are obtained. The charge distributions are correlated with various substituents, and are discussed with emphasis on the effects of phenyl substituents, hydrogen bonding, and formation of the sodium salt.     

Photon-echo detected nuclear quadrupole resonance spectroscopy

Rare-earth-ion-doped crystals (REICs) have played an important role in quantum information processing due to their excellent coherent properties. In order to obtain the information regarding the hyperfine structures of the rare-earth ions in REICs, optically detected nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) techniques based on RF resonance and various optical detection methods are widely employed in previous works. Here we demonstrate a new method of NQR spectroscopy based on the photon-echo detection. The hyperfine spectra of the ground state (⁷F₀) and the optically-excited state (⁵D₀) of ¹⁵¹Eu³⁺ in Y₂SiO₅ at zero field are obtained. This method can determine the hyperfine splittings within the ground state and the optically-excited state and is shown to be robust against electrical noise. Our results provide an alternative way for optical detection of NMR and NQR with high signal-to-noise ratio.     

Two-frequency effects in nuclear quadrupole resonance

A number of new effects which occur in the two-frequency excitation of a multilevel spin-system in nuclear quadrupole resonance are described. Three programs for observing the effect of trapping, used to detect some transitions in a multilevel system in terms of others, for an accurate determination of the asymmetry parameter of the gradient of the electric field, to identify lines of the multiplet spectrum of nuclear quadrupole resonance, and to investigate the phenomenon of cross-relaxation, are proposed. Quantitative estimates are given of the value of the trapping when two neighboring transitions are excited. The phenomenon of slow beats between signals of a two-frequency echo and the frequency of the transition ±3/2±5/2 for = 0 when an external magnetic field is applied is explained. The reason for the short spin-spin relaxation times in the secondary echoes is established. The experimental method and a block diagram of a two-frequency nuclear quadrupole resonance system are described.This paper was presented at an All-Union Symposium on Magnetic Relaxation in June 1971 in Leipzig.Translated from Izvestiya VUZ, Fizika, No. 3, pp. 82–88, March, 1973.In conclusion we wish to thank V. A. Shishkin, M. Z. Yusupov, and A. D. Gordeev, for their help and for useful discussions.     

Composite pulse trains for nuclear quadrupole resonance

In the present work, a multipulse train comprising {±^0°|2^90°-τ-±^180°|2^90°} and {±^0°|2^90°-τ-±^0°|2^270°} composite pulses is suggested for the observation of nuclear quadrupole resonance (NQR) signals from remote objects. It is shown that these pulse trains provide efficient separation of interference signals in the multipulse train, which allows conditions of NQR signal storage for detecting explosives to be improved. Kaliningrad State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 54–57, September, 1999.     

Nuclear quadrupole resonance in the gamma-resonance spectra of soft matter

It is shown that the harmonic librations (oscillations) of the principal axis of the electric field gradient tensor in “cages” of liquids, glasses, ferroliquids, and other “soft” systems qualitatively change the shape of the Mössbauer spectra of the quadrupole hyperfine structure. In addition to an effective decrease in the quadrupole coupling constant in the fast-libration limit, nuclear quadrupole resonance is predicted, which must be manifested in the Mössbauer spectra at the libration frequency that is approximately equal to the quadrupole splitting of spectral lines. By analogy with nuclear magnetic resonance, simple analytical expressions are derived, which describe resonance Mössbauer spectra in terms of the effective quadrupole coupling constant and the resonance splitting constant for the main lines. The observed features of the formation of quadrupole hyperfine structure spectra can be manifested in the Mössbauer spectra of soft matter and must be taken into account in analysis of experimental data.     

Determination of the asymmetry parameter of EFG tensor from moments of NQR nutation spectra in powders

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.     

Crossed-coil detection of two-photon excited nuclear quadrupole resonance

Applying a recently developed theoretical framework for determining two-photon excitation Hamiltonians using average Hamiltonian theory, we calculate the excitation produced by half-resonant irradiation of the pure quadrupole resonance of a spin-3/2 system. This formalism provides expressions for the single-quantum and double-quantum mutation frequencies as well as the Bloch-Siegert shift. The dependence of the excitation strength on RF field orientation and the appearance of the free-induction signal along an axis perpendicular to the excitation field provide an unmistakable signature of two-photon excitation. We demonstrate single- and double-quantum excitation in an axially symmetric system using 35Cl in a single crystal of potassium chlorate (omega(Q) = 28 MHz) with crossed-coil detection. A rotation plot verifies the orientation dependence of the two-photon excitation, and double-quantum coherences are observed directly with the application of a static external magnetic field.     

Capacitor-based detection of nuclear magnetization: nuclear quadrupole resonance of surfaces

We demonstrate excitation and detection of nuclear magnetization in a nuclear quadrupole resonance (NQR) experiment with a parallel plate capacitor, where the sample is located between the two capacitor plates and not in a coil as usually. While the sensitivity of this capacitor-based detection is found lower compared to an optimal coil-based detection of the same amount of sample, it becomes comparable in the case of very thin samples and even advantageous in the proximity of conducting bodies. This capacitor-based setup may find its application in acquisition of NQR signals from the surface layers on conducting bodies or in a portable tightly integrated nuclear magnetic resonance sensor.     

Determination of the local inhomogeneity of a crystal lattice using a two-frequency nuclear quadrupole resonance method

Nonuniform line broadening in quadrupole spin systems is analyzed. It is shown theoretically that this broadening is of the tensor type. This forms the basis of the method for analyzing the distribution of local inhomogeneities in the crystal lattice, which is verified experimentally on a sodium nitride sample.     

Nonstationary effects in nitrogen multipulsed nuclear quadrupole resonance

Multiple echoes in the envelope of the nuclear quadrupole resonance (NQR) signal were obtained in a field of multipulse sequences in powdered nitrogen-containing materials at room temperature. Echo signals were observed over a wide range of pulse rotation angles. It is shown that an analogue of the magic NMR echo can be obtained in the field of multipulse sequence.     

The two-frequency nuclear quadrupole resonance for explosives detection

The two-frequency nuclear quadrupole resonance (NQR) of¹⁴N nuclei is described for purposes of explosives detection. Two applications are known: two-frequency NQR for increasing the signal intensity, two-frequency NQR for improved reliability of explosives detection. The two-frequency experiments were carried out in hexahydro-1,3,5-trinitro-s-triazine C₃H₆N₆O₆ and sodium nitrite NaNO₂ as a substitute for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocycine C₄H₈N₈O₈. The two-frequency sequences for NQR are proposed for increasing the amplitude of NQR signal and improvement of detection condition.