halflifeとは 意味・読み方・使い方

語源

From half- +‎ life.

発音

• (米国発音) IPA: /ˈhæfˌlaɪf/

名詞

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.
   • 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, 2017, →ISBN, page 80:

     "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 and twenty-four thousand years respectively. So they stay hot for a long time."

   • 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 Oxidative Damage in Plants Under Stress, Springer, →ISBN, page 117:

     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.

2. (physical chemistry) In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
3. (medicine, pharmacology) The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity.
   • 2020, Dr. Alan Pateman, China, Covid-19, World Domination, Lulu Press, Inc, →ISBN:

     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.

4. The amount of time it takes for an idea or a fashion to lose half of its influential power.
   • 1991, Robert Ackerman, Introduction to Jane Ellen Harrison's Prolegomena to the Study of Greek Religion (1903)

     Most books of scholarship have surprisingly short intellectual half-lives during which they make a difference"

参考

• radioactivity