activity, A

https://dx.doi.org/10.1351/goldbook.A00114
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 = − d N d t. Synonymous with disintegration rate or decay rate.
Source:
PAC, 1994, 66, 2513 (Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)) on page 2515
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 960