relaxation time

https://doi.org/10.1351/goldbook.R05287
  1. In magnetic
    resonance
    spectroscopy
    the longitudinal
    relaxation
    time, T1, is associated with spin-lattice
    relaxation
    , and the transverse
    relaxation
    time, T2, with spin-spin
    relaxation
    . The definitions are: dMzdt=MzMz,eT1 and dMxdt=MxT2, where Mz and Mx are the components of magnetization parallel and perpendicular to the static field B and the subscript e denotes the equilibrium value.
    Source:
    Green Book, 2nd ed., p. 25 [Terms] [Book]
  2. In a chemical reaction, the time, τ, in which a concentration perturbation falls to 1e of its initial value.
    Source:
    Green Book, 2nd ed., p. 55 [Terms] [Book]
See also:
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 185 [Terms] [Paper]