decay time

in heterogenous catalysis
The time on stream during which the rate constant for the catalytic reaction, k, falls to a specified fraction of its original value, often 0.5.
PAC, 1976, 46, 71 (Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II: Heterogeneous Catalysis) on page 83