T2 RELAXATION DUE TO TWO-LEVEL FIELD FLUCTUATIONS

The NMR relaxation rates ${\mathrm{T}}_{1}$ and ${\mathrm{T}}_{2}$ are usually assumed to be proportional to the spectral density of the field fluctuations at some frequency ${\mathrm{\ensuremath{\omega}}}_{\mathrm{p}}$. While this is true for ${\mathrm{T}}_{1}$ (with ${\mathrm{\ensuremath{\omega}}}_{\mathrm{p}}$ the Larmor frequency), this study of ${\mathrm{T}}_{2}$ relaxation induced by two-level fluctuations of the z component of the magnetic field shows that ${\mathrm{T}}_{2}$ cannot be described by taking the spectral density function at any one frequency.