relaxation time

https://doi.org/10.1351/goldbook.R05287
  1. In magnetic resonance spectroscopy 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: \(\frac{\rm{d}M_{z}}{\rm{d}t} = -\frac{M_{z} - M_{z,\rm{e}}}{T_{1}}\) and \(\frac{\rm{d}M_{x}}{\rm{d}t} = -\frac{M_{x}}{T_{2}}\), 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 \(\frac{1}{\rm{e}}\) of its initial value.
    Sources:
    Green Book, 2nd ed., p. 55 [Terms] [Book]
    PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 185 [Terms] [Paper]