Term: activity, \(A\) https://doi.org/10.1351/goldbook.A00114 Definition: The number of nuclear decays occurring in a given quantity of material in a small time interval, divided by that time interval. Often, this term is referred to as absolute activity. Symbol A = -dN/dt. Synonymous with disintegration rate or decay rate. Related Terms: 1) nuclear decays (http://doi.org/10.1351/goldbook.N04227). 2) absolute activity (http://doi.org/10.1351/goldbook.A00019). Source: Green Book, 2nd ed., p. 22 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf) Citation: 'activity, \(A\)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.A00114 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.