Gaussian-approximation formalism for evaluating decay of NMR spin echoes.

摘要: We present a formalism for evaluating the amplitude of NMR spin echo and stimulated as function pulse spacings, situations in which nuclear spins experience an effective longitudinal magnetic field {ital h}{sub z}}({ital t}) resulting from arbitrary number independent sources, each characterized by its own time correlation function. The distribution accumulated phase angles ensemble at is approximated Gaussian. development motivated need to understand transverse relaxation {sup 89}Y YBa{sub 2}Cu{sub 3}O{sub 7}, experiences 63,65}Cu dipolar fields fluctuate due T}{sub 1} processes. applied successfully this example, case nuclei diffusing spatially varying field. Then we examine situation approximation fails{emdash}the classic problem chemical exchange dimethylformamide, where methyl protons shift fluctuates between two discrete values. In Gaussian yields monotonic decay with increasing spacing, while exact solution distinct {open_quote}{open_quote}beats{close_quote}{close_quote}more » height, confirm experimentally. light final example limits validity are discussed. {copyright} 1996 American Physical Society.}« less