Reciprocal of the decay constant of a radionuclide (
\(\lambda\)).
\(\tau = 1/\lambda\).
Note:
The mean life is greater than the half life of a radionuclide by the factor \(1/\ln 2 (\approx 1.44)\); the difference arises because of the weight given in the averaging process to the fraction of atoms that by chance survives for a long time.
Source:
PAC, 2021, 93, 69. 'Vocabulary of radioanalytical methods (IUPAC Recommendations 2020)' on page 86 (https://doi.org/10.1515/pac-2019-0302)