| def: Having been excited by the RF pulse, the nuclei turn back ("relax") to their initial state ( the initial equilibrium population) within usually several seconds when the induced magnetization decays. Since the precession of the nuclei is free and due to the decay of the induced magnetization the whole process is termed Free Induction Decay (FID). Usually, several FIDs are co-added in order to improve the signal-to-noise ratio of a spectrum. The summed up FID is then once subjected to a mathematical operation (Fourier transform) which results in an NMR spectrum.
synonym: 2D_FID |