Free induction decay (FID)

in NMR, the process of T1 and T2 relaxation which occurs after excitation of a spin system with a radiofrequency pulse at the Larmor frequency. The NMR signal obtained during a FID contains information only on the T2* relaxation, which is a result of the microscopic and macroscopic field inhomogeneities in the NMR, rather than T2 relaxation, which is the result of spin - spin interactions only (see T2 relaxation).

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