burn-up fraction

https://doi.org/10.1351/goldbook.B00764
The fraction of an initial quantity of a given nuclide that has undergone burn-up.
Source:
PAC, 1982, 54, 1533. 'Glossary of terms used in nuclear analytical chemistry (Provisional)' on page 1537 (https://doi.org/10.1351/pac198254081533)