Jakob Juul Larsen, M. Andy Kass, Denys Grombacher, Matthew P. Griffiths
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引用次数: 0
Abstract
The common understanding in surface nuclear magnetic resonance (NMR) is that the excitation pulse should be kept much shorter than the NMR relaxation times for an effective excitation. We present analytic, numerical, and experimental evidence demonstrating that this need not be so, and surface NMR signals can be retrieved even for absurdly long excitation pulses. We solve the Bloch equations in the limit of infinitely long excitation and use this result to demonstrate that a measurable magnetization can be obtained with long excitation pulses. We perform numerical simulations of the Bloch equations incorporating effects of relaxation-during-pulse, and our results suggest that long excitation pulses can be used to increase the depth of investigation, but that the spatial resolution of long pulse excitation is low. Data collected in Kompedal, Denmark using up to 3 s long excitation pulses provide experimental proof for the feasibility of long pulse surface NMR.
期刊介绍:
Geophysical Research Letters (GRL) publishes high-impact, innovative, and timely research on major scientific advances in all the major geoscience disciplines. Papers are communications-length articles and should have broad and immediate implications in their discipline or across the geosciences. GRLmaintains the fastest turn-around of all high-impact publications in the geosciences and works closely with authors to ensure broad visibility of top papers.