Title: decay constant
Long Title: IUPAC Gold Book - decay constant
DOI: 10.1351/goldbook.D01538
Status: current
Index: quantity

Definition
Proportionality constant relating the activity of a radioactive substance, A, to the number of decaying particles B, \(N_{\rm{B}}\), \(A=\lambda \ N_{\rm{B}}\). probability of a nuclear decay within a time interval divided by that time interval. Synonymous with 'disintegration constant'.

Related Terms
- nuclear decay: https://dev.goldbook.iupac.org/terms/view/N04227
- probability: https://dev.goldbook.iupac.org/terms/view/P04855
- radioactive: https://dev.goldbook.iupac.org/terms/view/R05077

Source
- Green Book, 2nd ed., p. 22 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)

Related References
- 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)

Other Outputs
- html: https://dev.goldbook.iupac.org/terms/view/D01538/html
- json: https://dev.goldbook.iupac.org/terms/view/D01538/json
- xml: https://dev.goldbook.iupac.org/terms/view/D01538/xml

Citation: Citation: 'decay constant' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.D01538
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Accessed: 2026-06-13T04:29:49+00:00