mean life

of a radionuclide
symbol: τ
synonyms: average life, average life of a radionuclide, lifetime, lifetime of a radionuclide
https://doi.org/10.1351/goldbook.08734
Reciprocal of the decay constant of a radionuclide (λ). τ=1/λ.
Note:
The mean life is greater than the half life of a radionuclide by the factor 1/ln⁡2(≈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 [Terms] [Paper]
Citation: 'mean life' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08734 RIS BibTex EndNote
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