Secondary echoes in three-frequency nuclear quadrupole resonance of spin-1 nuclei

Sauer, Karen L.; Suits, Bryan H.; Garroway, A. N.; Miller, Joel B.

doi:10.1063/1.1545442

Cited by 25 publications

(16 citation statements)

References 15 publications

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“…Thus, the complete saturation of the given transition is impossible. Despite a number of multifrequency experiments were carried out with RDX, no change of the NQR signal intensity was observed due to redistribution of the transition population densities [2,3]. Therefore, detection of this effect will allow one to use the methods of signal amplification on working transitions by preliminary changing the population densities.…”

Section: Physics Of Magneticmentioning

confidence: 71%

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Effect of 14N Nucleus Capture in Nuclear Quadrupole Resonance at Small Relaxation Parameters

2005

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Experiments on detecting induction signals of nuclear quadrupole resonance (NQR) on 14 N nuclei in hexahydro-1,3,5-trinitro-s-triazine C 3 H 6 N 6 O 6 (RDX) with preliminary changed population densities of NQR energy levels upon exposure to a saturating pulse are described. It is demonstrated that this actually causes the induction signal amplitude to change; however, complete saturation of the transition cannot be reached because of the NQR relaxation time. It is also demonstrated that the results of calculations without regard for the relaxation processes in RDX lack experimental support. Experimental data demonstrate the feasibility of application of the methods of preliminary change of the population densities (by pumping) for multifrequency experiments in NQR and explosive detection.In the method of direct NQR of 14 N with spins I = 1, simultaneously two and more transitions can be excited [1]. Interest in the application of multifrequency methods in this field has considerably increased recently [2]. This is primarily due to the possibility of detecting NQR signals on transitions unaffected by radio-frequency pulses [3]. This allows one to avoid the influence of the transition processes in the equipment and piezo-effects in various media. One of the best known applications of multifrequency NQR is attribution of spectral lines and change of the signal intensity for saturated adjacent transitions [4]. The last phenomenon is called capture in NQR. One of the methods of realizing this effect, in which a saturating pulse changing the initial energy level population densities is applied to the adjacent transition before the application of radio-frequency pulses, was suggested in [5]. In the present work, results of analogous experiments in hexahydro-1,3,5-trinitro-s-triazine C 3 H 6 N 6 O 6 (RDX) at room temperature are considered. Because RDX is a widespread explosive, results of our investigations can be used to increase the reliability of detection of this substance from two frequencies in the NQR spectrum.For spins Ι = 1 of the systems of 14 N nuclei, there is a system of three energy levels with frequencies of nuclear quadrupole resonance transitions [3] ( ) ( ) 0 , 3 , 3 2 4 4 eQq eQq eQqwhere zz eQq is the quadrupole interaction constant, η is the asymmetry parameter of the electric field gradient, and isPlanck's constant. The conditions and methods of 14 N capture in NQR must depend on the quadrupole system parameters. This is due to the fact that the spin temperature also depends on the relaxation parameters of the system. Having estimated the spin temperature T s for the corresponding transition, we can estimate the capabilities of changing the population density for the adjacent transition that can affect the NQR signal amplitude on the other transition. To this end, we take advantage of the following expression [6]:Kaliningrad State University.

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Section: Physics Of Magneticmentioning

confidence: 71%

“…Interest in the application of multifrequency methods in this field has considerably increased recently [2]. This is primarily due to the possibility of detecting NQR signals on transitions unaffected by radio-frequency pulses [3].…”

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confidence: 99%

Effect of 14N Nucleus Capture in Nuclear Quadrupole Resonance at Small Relaxation Parameters

2005

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“…Typical values of the magnetic field were about 2 mT. Total pulse lengths were as large as 1 ms, and the dead-time was on the order of 0.5 ms. We measured 7' 2* to be 3 ms, and T 2 has been previously shown to be on the order of 7 ms with a Gaussian decay [18], so that over the pulse lengths used here we expect some relaxation effects. Evidence for relaxation effects shows up as deviation from theoretical results, particularly at long pulse lengths.…”

Section: Resultsmentioning

confidence: 99%

Using quaternions to design composite pulses for spin-1 NQR

et al. 2004

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The fictitious spin-1/2 operators are well known to describe the evolution of a pure nuclear quadrupole resonance (NQR) system; particularly, the application of a radio-frequency pulse at one of the NQR transition frequencies is equivalent to a three-dimensional rotation in a space defined by the corresponding fictitious spin-l/2 operators. We demonstrate, theoretically and experimentally, that consecutive noncommuting rotations applied at the same transition frequency are well described by a single rotation given by quaternion parameterization of the rotations in fictitious spin-1/2 operator space. Thisnew route could greatly save computing time and efforts. We extend this approach to design composite pulses that compensate for the effects of the radio-frequency field inhomogeneity for a powder sample of spin-I nuclei.

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“…This magnetization achieves a maximum when the rotations angle in the sequence gr s = 180 ~ and depends on the resonance offset zXo)rp. This dependence shows that the multiplepulse regime can be applied for the investigation of the tensor of inhomogeneous broadening, correlation of this broadening at different transitions and the local distribution of impurities [14,17]. The experimental verification of these theoretical results will be given in future papers.…”

Section: Discussionmentioning

confidence: 99%

“…These operators describe the rotation in eight-dimensional spin space of a spin-1 nucleus and correspond to the SU(3) symmetry group [17,18]. This group includes seven SU(2) subgroups and seven subspaces spanned by three orthogonal operators, each forming a basis for representation of three-dimensional rotations [13].…”

Section: Appendixmentioning

confidence: 99%

Two-frequency multiple-pulse sequences in nitrogen-14 NQR

2004

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The theoretical investigation of the multiple-pulse sequences in which the radio-frequency pulses are applied simultaneously at two transitions are presented. The time-independent solution of the quantum Liouville equation for the average Hamiltonian of inhomogeneous broadening in the sequence is obtained by the projection operator technique. This solution predicts the multiple echo signals on the third transition that is not irradiated by radio-frequency pulses.

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Secondary echoes in three-frequency nuclear quadrupole resonance of spin-1 nuclei

Cited by 25 publications

References 15 publications

Effect of 14N Nucleus Capture in Nuclear Quadrupole Resonance at Small Relaxation Parameters

Effect of 14N Nucleus Capture in Nuclear Quadrupole Resonance at Small Relaxation Parameters

Using quaternions to design composite pulses for spin-1 NQR

Two-frequency multiple-pulse sequences in nitrogen-14 NQR

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