spinnrelaxation
Spin relaxation, sometimes misspelled as spinnrelaxation in informal contexts, is the process by which non-equilibrium spin populations and coherences return to thermal equilibrium with their surroundings after perturbation. In magnetic resonance techniques such as NMR and ESR, relaxation is described by two characteristic time constants: T1, the spin-lattice or longitudinal relaxation time, and T2, the spin-spin or transverse relaxation time. T1 describes the recovery of the component of magnetization along the external field as spins exchange energy with the lattice. T2 describes the decay of coherence perpendicular to the field due to spin-spin interactions and local field inhomogeneities; it sets an upper limit to signal decay independent of field inhomogeneity, though T2* includes inhomogeneities.
Relaxation mechanisms vary by system. Nuclear spin relaxation in solids and liquids is often governed by dipole-dipole
Experimentally, T1 is commonly measured by inversion-recovery or saturation-recovery sequences, while T2 is obtained from spin-echo
Spin relaxation plays a central role in determining spectral resolution and contrast in NMR and MRI, as