Time taken for the activity of a radionuclide in a specified place to halve its activity as a result of all relevant processes. Effective half-life Teff may be determined by:
;
[math] \frac{1}{T_{eff}}=\displaystyle \sum_{i} \frac{1}{T_{i}} [/math]
where Ti is the half-life for process i. Examples of the processes are physical decay of the radionuclide, physiological removal in the body and weathering in the environment.
ICRP Glossary entry - June 2019