decay constant

https://doi.org/10.1351/goldbook.D01538
Proportionality constant relating the activity of a radioactive substance, A, to the number of decaying particles B, \(N_{\text{B}}\),\(A=\lambda \ N_{\text{B}}\). probability of a nuclear decay within a time interval divided by that time interval. Synonymous with disintegration constant.
Source:
Green Book,2nd ed., p. 22 (https://www.cintegrado.com.br/site/documentos/green_book_2ed.pdf)
See also:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2518 (https://doi.org/10.1351/pac199466122513)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 968 (https://doi.org/10.1351/pac199668040957)