relaxation time

  1. In magnetic resonancespectroscopy the longitudinal relaxation time, T 1, is associated with spin-lattice relaxation, and the transverse relaxation time, T 2, with spin-spin relaxation. The definitions are: d M z d t = − M z − M z , e T 1 and d M x d t = − M x T 2, where M z and M x 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
  2. In a chemical reaction, the time, τ, in which a concentration perturbation falls to 1 e of its initial value.
Source:
Green Book, 2nd ed., p. 55
See also:
PAC, 1996, 68, 149 (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 185