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Spin diffusion and spin-lattice relaxation in solids containing paramagnetic impurities under influence of a multiple-pulse spin-locking radio-frequency sequence are studied theoretically and experimentally. The diffusion equation obtained provides a clue for determination of the time dependent magnetization. The spin-lattice relaxation time is calculated as a function of the correlation time and multiple-pulse field parameters. From the experimental data the spin diffusion coefficient, the radius of the spin diffusion barrier, and the correlation time for very slow molecular motion in polycrystalline (C(2)F)(n) system are estimated and found to be D~7.1×10(-12)cm(2)/s, r(c)~4.8×10(-10)m, and τ(c)~10.2μs, respectively.  相似文献   

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Significant artifacts arise in T(1rho)-weighted imaging when nutation angles suffer small deviations from their expected values. These artifacts vary with spin-locking time and amplitude, severely limiting attempts to perform quantitative imaging or measurement of T(1rho) relaxation times. A theoretical model explaining the origin of these artifacts is presented in the context of a T(1rho)-prepared fast spin-echo imaging sequence. Experimentally obtained artifacts are compared to those predicted by theory and related to B(1) inhomogeneity. Finally, a "self-compensating" spin-locking preparatory pulse cluster is presented, in which the second half of the spin-locking pulse is phase-shifted by 180 degrees. Use of this pulse sequence maintains relatively uniform signal intensity despite large variations in flip angle, greatly reducing artifacts in T(1rho)-weighted imaging.  相似文献   

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The behavior of nuclear quadrupole resonance (NQR) signals between RF pulses of the strong off-resonance comb (SORC) as well as the spin-locking spin-echo (SLSE) pulse sequences was studied as for 14N NQR line ν ?+? of dimethylnitramine (CH3)2NNO2 at 77 K. The periodic variation of the signal amplitude observed by using SORC pulse sequence could be reasonably explained by the theoretical expression reported in the literature.  相似文献   

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The non-markovian behaviour of coupled nuclear spins in the spin-locking experiment is investigated both experimentally and theoretically.  相似文献   

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The nuclear quadrupole resonance (NQR) method has been applied to Heroin Base (HB) to find an optimised multi-pulse technique for effective detection of HB. Experimental results of applying the proposed spin-locking multi-pulse (SLMP) technique to nitrogen-14 NQR in this sample are presented and convincingly demonstrate as a path towards efficient detection. A detection using a sequence of this character could be achieved over real-world scan volumes for screening of goods. All experiments were carried out at room temperature.  相似文献   

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A relaxation network has been calculated for multipolar AMX systems under application of a spin-locking RF field. Systems of this type are of interest in the study of proteins with fractional 2H enrichment. All possible auto- and cross-correlation terms involving dipolar, quadrupolar, and CSA interactions have been taken into account. The results show the presence of spectral densities at zero frequency for interactions associated with the locked nuclei, which are nonvanishing in the absence of fast motions. In addition, the application of a spin-locking field blocks certain cross-correlation interactions, thereby considerably simplifying the relaxation network.  相似文献   

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NQR Tomography     
In the interests of NQR tomography, theoretical formulas for calculating the concentration and spin-spin and spin-lattice relaxation times of local volumes containing quadrupole nuclei are derived from expressions for NQR echo-signals.  相似文献   

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The polarizations of spins in the local field hz? S(hz, t) (the layer polarization) are calculated. In terms of layer polarizations, the solid-echo formation mechanism and the transfer processes in multi-pulse NMR spin-locking are explained.  相似文献   

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NQR imaging based on spin precession in toggling reference frame and radio frequency field encoding is proposed. The profile of a NaNO2 monocrystalline phantom obtained using the method proposed is demonstrated. The application of the method in remote NQR detection and NMR surface coil techniques is suggested.  相似文献   

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Kaliningrad State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 62–65, July, 1992.  相似文献   

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The application of multiple-pulse sequences consisting of two-transition composite pulses for remote nuclear quadrupole resonance detection of explosives and narcotics is discussed. The pulse sequence for obtaining these pulses is described and it is shown that these pulses are equivalent to the pulse applied at the third (nonirradiated) transition. The loss of the signal intensity in this case is absent.  相似文献   

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This paper presents an analysis of the performance of frequency-modulated pulses and of pulses modulated simultaneously in amplitude and frequency in the pure nuclear quadrupolar resonance (NQR) spectroscopy of spin 3/2 nuclei. Computer simulations are given of the offset compensation efficiency of such pulses as applied to single crystals. Spin evolution equations were solved numerically. Experimental measurements, using FM pulses, of the35Cl NQR of sodium chlorate (NaClO3) single crystal and of mercuric chloride (HgCl2) powder are reported. The results suggest that frequency modulated pulses are alternative pulses to composite pulses in NQR.  相似文献   

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