half-life, \(\tau_{1/2}\)

of a transient entity
https://doi.org/10.1351/goldbook.HT07391
Time needed for a concentration of the entity to decrease to \(1/2\) of its original value.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 349 [Terms] [Paper]