## relaxation time

https://doi.org/10.1351/goldbook.R05287
1. In magnetic @[email protected] @[email protected] the longitudinal @[email protected] time, $$T_{1}$$, is associated with spin-lattice @[email protected], and the transverse @[email protected] time, $$T_{2}$$, with spin-spin @[email protected] The definitions are: $$\frac{\text{d}M_{z}}{\text{d}t} = -\frac{M_{z} - M_{z,\text{e}}}{T_{1}}$$ and $$\frac{\text{d}M_{x}}{\text{d}t} = -\frac{M_{x}}{T_{2}}$$, 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 [Terms] [Book]
2. In a chemical reaction, the time, $$\tau$$, in which a concentration perturbation falls to $$\frac{1}{\text{e}}$$ 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]