half-life

Noun

half-life (plural half-lives)

1. (nuclear physics) The time required for half the nuclei in a sample of an isotope to undergo radioactive decay.
   • "The guy that just left—what's he got in his lungs?" / "Well, I'm not very sure. But the two best candidates are uranium-233 and plutonium-239, one or both." / "They're in his bones too, aren't they?" / "Yeah, they're both boneseekers. And they've got half-lives of one hundred sixty-two thousand...1985, Michael Swanwick, “Boneseeker”, in In the Drift (New Ace Science Fiction Specials; series 3), New York, N.Y.: Ace Science Fiction Books, →ISBN; republished New York, N.Y.: Dover Publications...
   • O₂^(•−) and OH^• are highly unstable (half-life at the level of microseconds and nanoseconds, respectively) and cannot cross membrane, while H₂O₂, though not a free radical but a ROS, is relatively stable (half-life around 1 ms) (Møller et al. 2007) and can cross membranes through aquaporins.2015, Rup Kumar Kar, “ROS Signaling: Relevance with Site of Production and Metabolism of ROS”, in Dharmendra K. Gupta, José M. Palma, Francisco J. Corpas, editors, Reactive Oxygen Species and...
2. (physical) In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
3. The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity.
   • For nonporous surfaces such as steel, in a dark and low-humidity environment, the CCP virus has an 18-hour half-life—the time required for it to decrease by half , according to the researchers' findings.2020, Dr. Alan Pateman, China, Covid-19, World Domination, Lulu Press, Inc, →ISBN
4. The amount of time it takes for an idea or a fashion to lose half of its influential power.
   • Most books of scholarship have surprisingly short intellectual half-lives during which they make a difference"1991, Robert Ackerman, Introduction to Jane Ellen Harrison's Prolegomena to the Study of Greek Religion (1903)